Reviving Lime Mortar: A Stone Foundation's Best Friend

I am coming to the end of a long-term project involving the stone foundation that supports our early-1890’s home.  Looking around the city where I live, many 19th Century era stone foundations, and many brick homes and chimneys as well, are in dire need of repair, ours being no exception.  Originally bound together with a mixture of locally-sourced fired-limestone, sand and water, the joints between the stones had been long neglected and/or the sorry recipient of a common “repair” method involving cement-based mortar lain over the original lime mortar mix.  This post examines my ventures into the ancient world of lime mortar and the rekindling of a largely forgotten practice. 


Why our Foundation Declined

Contemporary masonry is focused largely upon mortars designed for concrete masonry units and modern super strength brick.  However, only a hundred years ago, mortars made from locally available limestone were the norm.   If given the proper attention, joints comprised of this fantastic material can last almost indefinitely.  However, if left to its own devices, weak lime-based mortar, like that used long-ago in our foundation, eventually turns to dust, degrading back into its component parts.  That’s what happened in our case – the natural process of decline dramatically accelerated thanks to three separate factors.

First, a lack of gutters on the building has for a long while permitted large amounts of rain water, concentrated by large sloping roofs, to fall more than two stories and splash back on the foundation, eroding the masonry in relatively short order.  [This deficiency has since been corrected.]

Secondly, in the intervening years since the building’s construction, few of the various owners of the property probably ever went through the effort of applying annual ‘whitewashes’ (a mixture of limestone and water) to the foundation to protect the underlying mortar – a necessity for the upkeep of weak lime mortar joints.  

And lastly, though well-intentioned, earlier work by some owner(s) or laborer(s) to shore up the masonry joints served to only exasperate the condition.  Soft stone (or brick) and cement-based mortars do not mix well.  Cured cement is very hard and very stable, while natural stone tends to (a) absorb water and (b) expand and contract along with rising and falling temperatures.  The incompatibility of these materials has not been widely known or necessarily understood by masons or homeowners, nor widely advertised by the cement industry.  This is simply evidenced by the fact that one cannot drop into their local hardware store and pickup a bag of anything but cement-based mortar.  The decline of the use of lime mortar is inversely proportional to the invention of Portland cement in the early to mid 1800’s.  Check out the Wikipedia entries for Portland cement and lime mortar for more on the history of each material. 


Before and After of North Wall:












Cement-based vs. Lime-Based Mortar

For the end-user, each type of mortar has their own advantages and disadvantages. 

Cement-based mortars offer higher strength, quicker set-times, and can be applied year round in cold climates as long as precautions are taken during set-up to protect the masonry joints from freezing temperatures.  However, they are also highly corrosive to skin and flora in its uncured “wet” state, destroy soft stone and brick masonry, offer a short working-window, and require a lot of energy to manufacture.

Lime-based mortars, on the other hand, must be protected from direct sunlight, drying winds, and rain for at least a week after application, and are really only practical for use in warmer climates or during the summer season in northern climates (the uncured mix does not fair well in cool to cold temperatures).  They do, however, allow 24-hour workability (as long as the mix is sealed in a fairly airtight container), produce incredibly long-lasting joints (since it ‘moves’ like the soft masonry units it joins and is ‘self-healing’), offer easy cleanup (since the wet mix is not nearly as damaging to skin or flora), and have a substantially smaller carbon footprint than their cement-based relatives.  Plus, lime mortars remove CO2 from the air far more effectively then cement-based mortars since the process most accurately mimics how shells are made (i.e. carbonation).  You can read more on the various processes that entail the manufacture of each material by viewing the above referenced Wikipedia links.

Saved Just in Time

Luckily, I got to our foundation just in time.  The cement-based mortar patching had almost completely caused the disintegration of the underlying lime mortar by allowing water in behind it, soaking the hidden lime mortar but not allowing it to readily dry.  This caused it to simply fall apart.  Many of the joints were vacant any mortar at all.  The seal between the cement and the stone failed since although the stone moved around, the cement mortar stayed in one place, cracking the seal.  This interaction also caused many of the stone faces and edges to disintegrate.  In effect, something had to give in this tug-of-war and the softer stone ended up suffering.  And of course this effectively widened the joints even further.  If you’ve ever seen a brick wall where the faces of many of the bricks are blown clear-off, you’ll understand the effect.  To reiterate, cement and soft stone/brick do not mix!


Before, In Progress, and After South Wall:

The “Lost” World of Lime Mortar

When I first looked into the world of lime mortar I was somewhat put off.  This was due to several realities.

1.  The material itself is presently hard to find, which is particularly tragic given the plethora of “Lime Kiln” roads that exist in our neck of the woods.  When I called my local masonry supply house and they had no idea what I was asking for, they wrongly tried to sell me masonry cement with lime in it (lime is sometimes added as an ingredient to increase the workability of certain cement-based mortars).

2.  Most of the information provided, by what centralized suppliers do exist (most are located in the mid-Atlantic states or on the west coast) or by the few trade organizations who have websites, has a very proprietary feel to it.  In other worlds, they’ll offer it for sale or discuss its benefits, but if you’re not “in the club” they’re not going to fill you in on the particulars of how to work with it, or will do their best to mystify its use.

3.  General lack of historical knowledge, by anyone I knew or had any contact with, about lime-based mortars.  This user-knowledge has not weathered the test of recent time well.

In the interest of overcoming these stumbling blocks for someone else, I am happy to not only explain where I ended up finding the stuff locally but also to pass along my experience in working with it.


Hydraulic Lime

The Lime Mortar

The particular lime mortar I ended up choosing is denoted as “NHL 3.5”, which stands for “Naturally Hydraulic Lime Mortar” with moderate hydraulic characteristics. 

For more info on what this means, and how it differs slightly from non-hydraulic lime mortar, I’ll once again point you in the direction of the Wikipedia Lime Mortar page.

At first glance, it appeared that my only option to get hold of any was to have it shipped by UPS from Virginia to our location in Vermont.  Since NHL 3.5 comes in 55lbs bags, I was not looking forward to the added freight cost.  After digging a bit more, however, I found out that the North American importer of the all-natural St. Austier lime mortar (a product of France) had an office in Montreal, Quebec.  It’s really too bad it was neither easy nor intuitive to find this out.  However, after some telephone calls and emailing, I ended-up driving the four hour round-trip with the trailer attached to our car and picked up all I needed for less then it would have cost to have it shipped.


Clean, Sharp, Well-Graded Sand?  What’s that?

Next, I had to find a local source of what all the retailers, and trade organizations, and product instructions I found online referred to as “clean, sharp, well-graded sand.”

I called the local sand pits, quarries and the masonry supply house, but no one had any idea if the various sands they offered met this definition.  I called the mid-Atlantic retailers (one of which actually manufactures their own line of domestic lime putty – most is imported) but they only deepened my confusion, echoing as they did the “clean, sharp, well-graded” mantra while also supplying to me the largely useless ASTM specification.  Sandpit operators in my area apparently have no idea what “ASTM C144-04” refers to, nor do I.

I finally secured the foolishly simple answer to this bizarrely mysterious question by locating and then getting in touch with a renowned mason in our area with experience in historic preservation.  He was generous enough to return my cold call and during our conversation effectively ‘spilled the beans’.  His advice arrived, “…we always use masonry sand and we just add some larger aggregate for filling larger joints.”  I thanked him, and also quietly thanked my lucky stars for my propensity and tenacity to get at the truth.  Otherwise, I’d likely still be searching for the ridiculously elusive “clean, sharp, well-graded sand.”  Why no one else just called it what it is I’ll never know.  I paid my local concrete yard a visit and took away all the masonry sand I would need for a small fee.


Preparing the Foundation Walls

Then, it came time to actually prepare the foundation walls for the new mortar.

I got a kick out of the many references I came across online that practically forbade the use, by any self-respecting mason, of pneumatic chisels for removing old mortar.  Now, had I heeded that advice, I’d still be at work on my first section of wall.  Of course, I’ve since come to realize, through experience and by reading between the lines, that the widespread concern is wholly unfounded for stone walls.  Although the focus for all of these warnings was originally brick walls (where it is completely valid), somehow, over time, the original intent was lost in translation and the moratorium was extended to stone walls.

I personally found using a pneumatic chisel to be the best, most effective way to remove the hard cement mortar and the failed lime mortar in preparation for the new joint.  To then remove the left-over residue, I used a spray of high pressure air provided by attaching a spray nozzle to my compressor hose.  For interior work, I supplemented a shop-vac for this portion to keep from blowing dust all over the place.


Prepared West Wall and Finished West Wall:










Preparing the Mortar

Lastly, I prepared the new mortar using a ratio of 2.5:1, sand to lime.

I mixed batches in a steel wheelbarrow with a hoe and either transferred the mortar to a smaller container which I fed in through a basement window (for interior work) or simply troweled the mix right out of the barrow.  I made sure to thoroughly soak the portion of the wall that I was working on with a garden hose (outdoors) or a spray bottle (indoors) shortly before packing in the new mortar, and to then keep the wall moist as I worked.

Per the suggested practice I worked in “lifts”, filling the joints approximately half or two-thirds full on my first pass, then returning to where I’d started to go over the joints again with the finish layer.  There are many cautions about mixing the mortar too wet, but in my experience the only negatives a too-wet mortar would suffer from was that it made it harder to pack into the joints (too soupy) and that it would crack a little as it dried.  A couple of times I used a wetter mix for an initial lift and then simply smoothed over any cracks while using a dryer mix for the second lift.  No big deal.


Prepared North Wall & Finished North Wall












Final Steps

When the joints were full to my satisfaction, I covered the portion of the wall I had finished with plastic tarps touching or almost touching the wall.

Approximately 24-hours later I returned to remove the tarps and using a stiff brush, brushed the joints, cleaning them up while removing any errant mortar from the face of the stone.  A couple of times I waited for ~35 hours before I completed this step since the walls on the north side of the house took longer to cure to the point where brushing could occur.  I realized the necessity of waiting longer when I began to brush the wall and too much mortar was removed.  So, in these instances, I simply waited another night and the next morning or mid-morning finished the process.

After the brushing, I reinstalled the tarps and left the wall(s) covered for seven days.  On the south side of the house, which is in direct sunlight, I used drop cloths soaked in water in between the tarps and the wall and then soaked them daily for the first few days to keep the walls from drying too quickly.  Elsewhere, I just used the plastic tarps and occasionally (once a day for the first few days) sprayed the walls lightly with a garden hose.  Indoors, I left the walls uncovered, but made sure to keep the basement windows closed which seemed to afford a humid enough environment for proper curing.

A week later, I removed the coverings and, in our case, added a band of ¾” crushed stone up against the foundation and extending outwards approximately two and a half feet, bordering the entire foundation.  Since I’d excavated approximately a foot to a foot and a half below grade to get at more of the foundation for re-pointing, I simply took the excavated soil off-site and filled the space back in with crushed stone after grading the soil base away from the house and tamping it down.  I figured that it would be good for the foundation joints I’d re-pointed to be able to breath (for drying) and the addition of the stone perimeter really cleaned up the look around the foundation.

All-in-all, this was a fairly simple and straight forward job but one that did take some time and required a little patience.  I highly suggest lime mortar for anyone working with stone and look forward to using it in future projects.


Tree root growing along Foundation, In Progress, and Finished North Wall



114 comments to Reviving Lime Mortar: A Stone Foundation’s Best Friend

  • Eric

    Very nice work, looks great.

  • Chris

    Hello Eric,

    I’m writing to you because I just stumbled across your blog and find myself in exactly the same situation as you were in. I however am located in Montreal and still can’t seem to find anywhere to buy Saint Astier NHL 3.5 locally. It seems the only distributor is located in Etobicoke Ontario and would require me to ship a large number of very heavy bags to Montreal, obviously I would prefer to avoid this if possible.

    Where did you get your NHL 3.5 from in Montreal?


    • Kai

      Hi Chris – This is Kai.

      the website for the distributor, Daubois Inc.,that I bought my lime from in Montreal. They didn’t require a minimum quantity and they had plenty in stock. Let me know if you have any additional questions.

      Thanks for visiting our site. Good Luck on your project!

  • The project looks great. It’s also good to know that NHL is catching on in the North America. I’m a representative of LimeWorks.Us located in Pennsylvania and we can assist homeowners, contractors and architects with trying to find NHL near Pennsylvania. We also provide color-matching of lime mortars, Stuccos and suggest appropriate mix designs.

    • That looks like a great option for folks living in that area Randy – thanks for telling our readers about it. We also noticed that you utilize a 100% wind powered web host & offer a 2% “Awareness Rebate” on all Natural Hydraulic Lime orders – very nice.

    • chris gall

      I am a concrete contracter who does a lot of sandblasting but very little pointing . I have a 210 yr old barn that I chipped and sandblasted but am afraid of repointing because of misinformation on material to use call me collect(if they still do that) I would love to talk pointing thanks chris dolyestown pa thanks

  • George

    Thank you for sharing your project! I do have a question on how you mixed your mortar. When dividing out the lime and sand by volume, was the lime still in powder form or was it putty at that time?
    My house has a very old foundation wall similar to yours. I was thinking of going with a lime (s grade) and sand mix and am having trouble finding mix instruction without Portland added.
    I did look at, their products would fit my needs beautifully with the exception of cost with shipping to Minnesota. I would welcome any suggestions or advice. I will be emailing Limeworks as well. Hopefully they will reply here to so more people can find them as I did 🙂

    • Kai


      Thanks for visiting our site and for your comments and questions. Natural Hydraulic Lime Mortar (NHL) comes in powder form and is as easy to worth with as cement-based mortars (even easier in my opinion). Every time I washed my tools I did so on the lawn without fear of killing grass and plants (like cement has the habit of doing). NHL is not nearly as caustic as quick lime/lime putty either. No fear of crazy heat or boiling water. As for sourcing, you’ll need to find a distributor since I doubt even your local masonry supply store will know what your talking about. To recount, my local shop (all they do is masonry supply) had no idea what I was talking about! Definitely email Limeworks (I’d call them too) but don’t hesitate to get in touch with the importer of St Astier NHL out in Petaluma, California (, they’re the folks I ended up dealing with (actually their Montreal, Canada distributor). Check out their “Distributor” page to find the office closest to you. My impression is that TransMineral USA is a much larger operation than Limeworks so they may be better able to meet your needs. That said, if you haven’t already done so, I’d at least get a quote from Limeworks to have something to work off from. The nice thing about their product is that its not imported. Having Montreal so close by clinched the deal for me, even though I would have preferred a domestic product.

      Here’s a great primer that recently popped up online about NHL:

      Let me know if you have any further questions. 🙂

      • HI Kai,

        Just wanted to mention that we are a retailer of Saint Astier products in Canada with offices in Toronto and Montreal, We work wit Saint Asiter to reduce significantly the price of NHL in Canada and we offer now a reduced pricing on all natural lime plasters. We have dedicated offer for large jobs and we import the lime directly from France thus reducing the cost of shipping. You can find more information at



  • Kris

    I could seriously hug you. THANK YOU for the awesome blog on repairing stone walls. My limestone foundation looks exactly like yours (the before pictures) and I’m now researching the best way to repair. Unfortunately, I did portland on the barn foundation a few years ago and while I don’t *see* problems yet, I am way relieved to find your resource here and not make the same mistake on the house base, which is circa 1900. Like George, I’m in the midwest (Iowa) and will refer to your supplier references above to acquire the NHL. Thanks again! Kris

    • Kai


      I had no idea when I posted my lime mortar experience that so many people would find it so useful! I am truly humbled. Good luck on your project and I hope you enjoy using NHL as much as I did. Its great stuff!

  • Kris

    Thanks very much Kai. I found a supplier about 1.5 hrs away. Definitely worth an afternoon’s ride–and thanks very much again for a GREAT blog!!!

  • Tom

    Hi Kai,

    This is a great documentation of how you repointed your old foundation with Lime Mortar – thanks for taking the time to make this public.

    I have a question about your crushed stone around the perimeter of your house. I’m wondering how you came up with this idea or is this practice somewhere? it certainly looks neat and clean and I would imagine the foundation could breathe after you repointed, but, doesn’t this also allow water a path of least resistance right to your foundation?

    My family moved into an 1840’s colonial about 2 years ago. Your suggestions of dealing with water source first were right on. We diverted all downspouts to underground piping which we had installed and roof runoff is now carried well away from our foundation. We unclogged the gutters which was a huge source of water sheeting off the sides of our home and now are looking at installing oversized gutters as our home has little to no eaves/roof overhang. We’ve also installed a dehumidifier and our basement is now nice and dry. We only suffer from some deterioration in our basement of the joints surface, flaking, previous patches and layers of white-wash or paint.

    Your account is quite exciting to see and makes us eager to move on to the next step in our restoration for both interior and exterior. I think this post will be helpful to so many people who researching appropriate restoration of their old home.

    • Kai


      My pleasure and thank you for your comment. You are quite correct that the crushed stone around the perimeter of the building serves several purposes. First, as you pointed out, its looks nice. Second, the base of the trench I dug that the stone was then laid into is hard tamped earth (with a consistency much like sure pack) that I compound beveled – IOW it is sloped both away from the house and down hill from the house. The crushed stone is highly permeable (which allows rain and snow melt to quickly make its way down to the sloping surface) and the hard tamped earth is not (which allows any water to flow away from the house). We are blessed with good soil, the upper several or more feet of which drains remarkably well (lots of sand mixed in thanks likely to the last ice age) so there was no need to add any mechanical drainage (pipes and such). Third, and as you also point out, the crushed stone allows the sub-grade portion of the foundation wall to breath really well which I am guessing aids in drying it out after precipitation events and in the winter when any moisture in the basement and/or the foundation wall “dries to the exterior” (‘building science‘ stuff). And finally, fourth, the crushed stone perimeter also acts as, for lack of a better term, a “drip line”. Although we completely re-sided, re-trimmed, re-windowed, re-flashed, and guttered the entire house, adding a crushed stone drip line around the entire footprint is a recommended practice for any house built prior to 1978, the year that lead was banned from residential paint.

      Your home may about 50 years on ours but since they really knew what they were doing back then I am sure your restoration, like ours, will be more than worth your while. One last thing, if you haven’t done so already, try and get your hands on a copy of the Building Science Corporation’s “Building Guide” appropriate to the climate zone where your home is located. I have found their information invaluable and recommend their studies to anyone undertaking any renovation/restoration work (plus, of course, new-construction as well). While all of the pertinent info is freely available on their site, the guides are handy because that they tell you everything you need to know all in one book.

      Have fun and good luck! 🙂

  • tim

    If you push the mortar into the joints with a pointing tool and mortar hawk then you can leave the mortar neatly inside the joints instead of smeared over the stone faces. This could give a more visually appealing appearance and highlights the attractiveness of the stone faces. You’ve hidden the stone faces too much. But, it takes a lot more time to do it the way I’m suggesting.

  • tim

    “If the old bricks or stones have worn, rounded edges, it is best to RECESS the final mortar slightly from the FACE of the masonry. This treatment will help avoid a joint which is visually wider than the actual joint; it also will avoid creation of a large, thin featheredge which is easily damaged, thus admitting water. After tooling, excess mortar can be removed from the edge of the joint by brushing with a natural bristle or nylon brush. Metal bristle brushes should never be used on historic masonry”

    And, the stone faces will look nicer if you recess the mortar into the stones. If you smear the mortar all over the stone faces you create a sloppy appearance and you create mortar exposure that is too thick and too thin in various locations which is more likely to crack or break off.


    • Kai

      Tim, thanks for both of you comments. I hear you loud and clear. However, in my defense, since the square edges of the most all of the stones had been damaged by the earlier use of cement based mortar (and since the particular type of stone used in the wall is quite soft and its edges very brittle) I had little choice but to fill the entire void with mortar and small stones (the stones are hidden in the mortar). As it was, I scrubbed every joint with a stiff bristled brush when the mortar had cured enough to be solid but not so much that it was no longer “brush-able” in order to prevent the thin feathered edges you refer to. Also, leaving out more mortar would have resulted in a very sunken look to the wall which in my opinion just did not ‘look’ right. You’ll recall that I laid the mortar in in multiple layers or “lifts”; the first to last lift left a lot of rough and brittle edges visible – plus it just didn’t look right – so I added another. I guess personal preference played more of a role in the eventual outcome than I may have otherwise realized. Thanks again for your insights.

  • joyce

    Thanks Kai for being so detailed in your limestone repair information. Recently purchased a home in Winnipeg, built in 1913, and have started removing the failing mortar in the basement. We have been reading lots of info on the internet about the importance of using the lime based mortar for the repairs. But when you go to purchase the material needed we are getting confused about what to buy and the associates at the retail stores do not feel confident enough about this subject to be any assistance. What was your ratio? Did you use water only for moisture or did you add a liquid for adhesive acceleration?

    • Kai


      The ratio I used is 2.5:1, sand to lime. I used only water. I don’t recall seeing any mention of synthetic additives in any of the research I did into lime mortar. That said, I am aware of additives available for cement-based mortars (like latex and or lime to improve elasticity). But these are usually added to cement-based mortar to give it qualities akin to lime mortar. I don’t think there’s any reason to ruin the all-natural lime mortar ingredient list that’s worked so well for thousands of years. I would advise that you do your own research before adding anything synthetic to your mix. I also highly suggest that you get in touch with at least one of the retailers I reference in my post to pick their brains. Finding anyone locally who has any actual experience with lime mortar can be very difficult.

      Good luck! 🙂

      • Marion Nesbitt

        Hi Kai – Great info. I know it is some years past your posting, but perhaps you could help me. My house was built 1910. Stone foundation, brick on top. Has weeping tiles. One corner is settling. Have done interior and exterior repairs to cracking. This dry summer, again more serious cracking in foundation, brick exterior, and basement floor. I think the pilings or something have to be reinforced. Do you know what company can raise or reinforce to stop further settling in Winnipeg?

        • Kai

          Marion – Being that I am not from Winnipeg (or Canada for that matter) I haven’t the foggiest idea. It sounds to me like you’ll just need to make some calls and gather some bids. Good luck on your project! 🙂

        • Seanna

          Hey everybody,
          I usually never write any reviews whatsoever. After reading all this great and helpful information I look forward to putting it to use when we build our home in the future. I just wanted to mention the reason I even looked into limestone for a foundation? I saw a program years ago that referenced a cabin that have been built quite a long time ago let’s just say at least a hundred years ago. The cabin had Logs with bark still attached to them. Not sure the type of wood? The reason all of this was able to stay intact and was not ever damaged by termites is, apparently termites will not come up a limestone foundation and I was not aware of this. But I found it fascinating and have always been interested in using these products for my own home.
          Thank you again this information is still serving people.

        • Kai

          Thanks for your comment Seanna! That’s fascinating – we hadn’t come across that before and look forward to others chiming in. 🙂

    • Hi Joyce,

      We are a retailer of Lime Mortar in Canada, EcoBuildingStore, and we would be happy to answer any questions you may have. We are located in both Toronto and Montreal, and have also worked with a few clients in the Winnipeg area with Natural Hydraulic Lime.

      In regard to finding someone local with experience, we currently have one of our representatives working on a straw bale home with Natural Hydraulic Lime in Martock (near Winnipeg Beach). He will be there until the end of next week (Nov 30th), and if you were interested in consulting with a professional we can try to arrange something for you.

      Give us a call anytime at 1-877-524-8583 with some more details about your project and hopefully we can help you out! You may ask for myself, Jonathan.

  • Amnon

    I’m going thru the same process of repairing old stone foundation and was wondering if hydrated lime by Texas lime company (sold at the Home Depot) or Quikrete hydrated lime type S (sold at Lows) can be used for the mortar mix
    thank you

    • Kai

      Great question and thanks for visiting our site!

      I checked out the website of the Texas Lime Company’s parent company (USLM – United States Lime and Minerals, Inc.) and the product data sheet for Quikrete’s “Hydrated Lime Type S“. Depending on your particular application you could use either TLM’s “High Calcium Quicklime” product (but be prepared to slake it!), or either TLM’s factory-slaked product “Hydrated Lime” OR Quikrete’s factory-slaked hydrated lime product “Type S”. The only thing to keep in mind is that none of these products in their stock form will impart the unique features offered by hydraulic lime, the product I blogged about above.

      Hydraulic lime is limestone that contains naturally occurring metals like aluminum or silica or, in the case of manufactured hydraulic lime, that contain materials like fly-ash or volcanic ash which themselves contain heavy metals and impart similar attributes to naturally occurring hydraulic lime. As stated on Singleton Birch’s UK webiste:

      “Hydraulic lime has a degree of cementitious set when in contact with water (or atmospheric moisture), it also sets by combining with atmospheric carbon dioxide to some degree. Hydrated lime does not set in the prescence of water, it sets by combining with carbon dioxide in the atmosphere to turn back into chalk or limestone.”

      So, IOW, non-hydraulic lime mortar (IOW pure limestone) cures/dries primarily by absorbing CO2 (carbonation) whilst hydraulic lime (IOW impure limestone contaminated with metals) cures/dries primarily with the addition of water (like cement-based mortars) followed by a process of carbonation.

      Hydraulic lime sets underwater which makes it particularly useful for below grade applications and is also much stronger and longer lasting when compared to hydrated lime. However since hydraulic lime is not available everywhere, likely having to travel great distances to get to your door, the cost differential between a local or domestic non-hydraulic lime mortar and an imported or manufactured hydraulic lime mortar will be substantial. I chose the hydraulic product because of Vermont’s wet climate and its proclivity to extreme freeze/thaw events. Somewhere absent the freeze-thaw cycle might very well preclude the need for a hydraulic product.

      So, getting back to your question, it all depends on what you are looking for. Non-hydraulic lime can of course be used below grade (the old-timers did it!) but it won’t hold up in this application nearly as long or as well as hydraulic lime, requiring shorter intervals between re-pointing. Said another way, chances are that if where you live is absent any naturally occurring hydraulic limestone formations, then the existing mortar in the foundation you’re working on almost likely utilized non-hydraulic lime, which likely lasted a good long while but won’t last as long as hydraulic lime. But if you have a local source of non-hydraulic lime and are trying to stick to local materials and/or matching existing work than I’d go with the local supply out of respect for the past and to minimize the project’s carbon footprint. Either way, you’ll likely be long gone before the foundation needs any additional work! Good luck on your project! 🙂

      Here’s a good primer on lime mortars that you may find helpful:

      And whatever you do, make sure to study up on the processes of using these products as they all require more care and oversight than cement-based mortars.

  • Amnon

    Thank you very much Kai that’s very helpful … you convinced me…. I will check if I can get Hydraulic lime anywhere around NYC. Are you in the construction building trade or just learned all this out of necessity?
    I have two more questions…. Doing foundation mortar repairs, is it recommended to excavate the exterior side of the wall to do pointing underground or not? I thought I read in one of the blogs that it’s not recommended to disturb the soil but I’m wondering what you think.
    2nd question, how do you measure the portions of the mortar mix components? Is it just using a measuring cup and taking 1 cup of lime and 3 cups of sand? Do I use dry mason sand? (I guess its three questions)
    Thank you so much for taking the time and doing the research, I really appreciate it

    • Kai

      To answer your questions:

      1) I have both professional and personal experience in both arenas.

      2) As for excavating the exterior side of the wall, I did so for one major reason. I wanted the ground adjacent to the foundation to more readily shed water. I have a feeling that whether or not this practice is encouraged or frowned upon has a lot to do with a) who is commenting on the matter, b) the age and type of property in question and c) the qualifications (or lack thereof) of the person(s) that will be performing the actual work.

      3) On the matter of measuring portions, I simply used an empty plastic nine-pound peanut butter container (unsure of the fluid quantity – probably around a gallon or so) as my oversized ‘measuring cup’. I used a smaller container to transfer the lime powder out of the bags it came in and into the peanut butter container for measuring purposes (which I then dumped along with the sand into a steel wheel-barrow for mixing). This is not a perfect science, a little variation won’t destroy your mix, but its helpful to make the process simpler and more robust by sticking to something that allows quantifiable measuring. Doing so will also help maintain a uniform final product. I think its unsightly when variation in mortar mix is noticeable in a wall.

      4) I used, and the manufacturers recommend, sharp well-graded sand, a.k.a mansonry sand. As far as the sand’s moisture content, its not an issue since the mix will determine how much water is necessary to get to the desired consistency. A wetter sand will simply result in less water needing to be added to a given batch of mix. Hope that makes sense. The first few times you mix a batch you’ll become an expert on the ratio of dry to wet. Just jump in and you’ll be sure to figure it out. Keep in mind that is a natural material so its fairly forgiving! 🙂

      • Matt

        Actually the moisture content of the sand DOES play a role – but first I wanted to define “well graded” sand and why it’s important. What well graded means is that it has a range of grain sizes from pretty fine to fairly coarse and everything in between. The reason this is a good thing is it packs in tighter, leaving fewer voids. Think of a room full of basketballs – plenty of air space no matter how tight you pack them. But mix in some golf balls, marbles, etc and you’ve got a much more solidly packed volume.

        The reason moisture content does matter is that moist sand will have more volume than dry or wet sand (which will generally have about the same volume), especially with a well graded sand. This is because the partial moisture reduces the fluidity of the sand, keeping it from settling completely. No, it won’t make much difference in terms of your water content in your mix but moist sand measured by volume will be different from dry sand measured by volume so the ratio of lime to sand will be off.

        To find the correct ratio of lime to sand, fill a glass of a known volume with your sand. Slowly add water from a graduated container until the water JUST reaches the top. The ratio of water to sand will become your lime to sand ratio. We want just enough lime to completely fill the voids, but no more. If you don’t want to go through all that trouble, 1:2.5 or 3 is probably a good place to start though.

        Hope this helps.

  • Tom M

    Just to tac on to the discussion, i’m also in the New York area and have found a company called limeworks who sells a line of Hydraulic Lime products. They have a range from NHL 2, 3.5 to 5. They descriptions do get a bit technical and vague at the same time so i’m not exactly sure which might be best for my application. Similar to Kai i’m patching/repointing the exterior of a fieldstone foundation from the 1850’s. I must say it’s in darn good shape and in no major state of decay but this is the point were I need to fill some gaps, remove some loose mortar and overall clean up the appearance. I hope you don’t mind me providing the links, I have not used this companies products or services so i provide as information only.

    • Kai

      Tom – thanks for adding your comment. I considered the folks at Limeworks but in the end the cost to ship versus my driving to pick material up myself was the determining factor. Of course, I had somewhere nearby that stocked the product. But there’s got to be somebody in NYC or nearby environs that stocks this material. Just think of the millions of square feet of lime-mortared walls just in Manhattan churches and other pre-1900 buildings! I’d say keep searching for a local supplier to avoid having to pay shipping. Thanks again!

  • Amnon

    First thank you Kai for all the advise, I finally purchased few bags of NHL from Limeworks (paid shipping but at least it was fast)and I’m ready to start my work. since weather is getting cold I will work on the inside first and keep the exterior for the spring. In my investigation I came across This Old House video explaining how to re-point an old field stone foundation and found that they were using a Quikrete type S mortar and was wondering why…..

  • Marcus

    Excellent resource, I have had multiple masons look at my 1900 field stone foundation and all planed to use type s mortar with OPC. Even the local masonry supply houses were pushing me in that direction, I personally felt that it was wrong but for structural security have commissioned a mason to do a patch and interior repair on about 20ft wide section that was in very poor shape. With the info you have provided I plan to attack the rest of the basement myself, but have one question for you. From your knowledge thus far, how long do you think the type s OPC mortar repair work will last? Most of it had no remaining lime mortar, so the voids were packed full. In a couple of places the lime mortar was chiseled back to give a key for the type s to bite. I’m thinking that this might be a good temporary repair and that I should put it on the 5-10 year plan to come back and knock it out and do it right. But, that gives me 5 years to work around the basement and do the interior and exterior properly the first time.

    • Kai

      Thanks for your question. The angle I approached this issue from was damage to the stones used in the foundation. Cement-based mortars are very hard and unforgiving when it comes to softer stones like those used in our foundation – the stones move a lot during freeze-thaw events whilst the cement mortar does not, which causes the faces of the stones to disintegrate. When used with compatible masonry (e.g. modern brick and block) and if not subjected to freeze-thaw cycles, below grade conditions, or consistent and/or excessive wetting, cement mortars can last up to a half-century. Your particular application will determine the probable lifespan. Are you unable to convince any masons in your area to use lime mortar? I imagine that you’d prefer to only have to spend the money once. Just wondering. 🙂

  • east coast slinger

    Great job on the topic,sorry to say but you basically took a gorgeous stone wall and ruined it with the over flush joint smear!! Masonry is a skilled trade which is gained through ” HANDS ON ” experience especially the fine art of restoration..This is an example of where you need to #1= hire a skilled pro or #2= at least consult with a pro for tips and maybe some hands on training etc.. i do commend you on your ” diy” efforts.. i would consult with a masonry restoration consultant to have them clean up the smeared stone such as ” detailed sand blasting and or cleaning “…masonry= of course its not rocket science…anybody can bolt together a rocket..

    • Kai

      Thanks for your input. I’m very happy with the results, with how much money we saved and with the fact that I learned a new skill.

      • Shelly

        I think you achieved wonderful results! I would like the address of the Lime supplier in Virginia if you have it, thank you

        • Kai

          Shelly – The web address you’re requesting is, however, a quick try shows that the site is down. Don’t know if this is perhaps why you’re asking for the address (thinking that perhaps the one listed in the comments above is incorrect) but I’d keep trying it for a few days and/or calling the retailer’s telephone number which is 843-five seven seven-6671. Good luck! 🙂

    • G. Briggs

      The mortar should have been tinted so that it didn’t have that ugly new white look.

      • Jonny K.

        Kai gets an ” A+ ” for research an effort. Unfortunately gets an ” F ” for end result. This proves to show you can research endlessly on the web for great info and become an internet keyboard genius.But if you have no proper hands training from a experienced pro, there is a pretty good chance you fall into the ” epic failure category” of diy’s .Word to the wise, if you have a property of historic value please think twice before attempting something like this especially if you have 0% hands on experience, knowledge of stone masonry and a little structural foundation engineering whit.The same as, ” you can’t properly and safely learn how to fly a jet by watching youtube videos, right kai ? 😉 lol … Sorry my friend but this is a sloppy mess and the other diy’s commenting on here are just too naive to know any better. MY experience = 35 years in the trade with majority focus on restoration,preservation,inspection, instruction etc. Approx over 50% of my contractual work is from failed attempts from the homeowner or from a non journeyman level mason not experienced nor properly trained or educated . There is no such thing as saving money when it comes to ” restoration “. Its about an investment to have it done right the first time , while many spend twice. 😉

        • Kai

          As far as a response to your criticism please see my reply to “east coast slinger” above.

          P.S. Not to downplay the wisdom that can only be gained by specializing in and practicing something for many years, it is in fact possible to learn to safely fly a jet by watching videos and using a US$40 PC-based flight simulator.

        • Marcus

          Johnny K,
          I found your comments disrespectful and ultimately of little value to this board and the people that have visited it. It is impressive that Kai approved the post and did not simply delete your comment outright.

          As you have decades of experience, I am surprised that you were searching for information on this topic and stumbled upon this message board. As you did take the time to read his notes and write a post, I would assume that your post was intended to illustrate the vast domain knowledge and skills you have in this space, with the chance that you might create awareness of your capabilities for a future client?

          Perhaps, rather than ridiculing Kai’s work, you could instead demonstrate your superior knowledge and share with us all what you would specifically have done differently. This would then make your post a meaningful contribution to this community.

          If you are a skilled contractor in this space, would you share your name, license number contact details and region of operation. I expect many home owners land here because they think they can do this themselves and then fafter reading Kai’s great resources they may opt to hire someone in the end. I certainly did as it was more labor intensive than i had time for. So, rather than simply critiqing Kai’s diy efforts, educate us on what the pro approach is – add something of value to this board and provide a way for potential clients to connect with you.

          For clarity my name is Marcus, I’m a home owner of a 1900 multi family in Massachusetts, I’m not a contractor, but my father is and doing DIY renovation of my home is my hobby. I’m the classic weekend warrior and I try my had at most trades, if I screw it up and have to hire someone to fix it… So, be it… All part of the fun.

    • william

      You can use murcuric acid to wash the stone. be careful it is dangerous and toxic . But watered down can be brushed on the stone it will eat away the residue of the mortar. be sure to rinse. a respirator and gloves and eye protection is required

  • […] product (i.e., any of the pre-mixed mortars that are used in contemporary construction) is a really bad idea because the concrete with trap moisture behind it, causing the rest of the lime mortar to quickly […]

  • Joe

    Hi Kai,

    I really appreciate this page you put together. My house was built in 1852 and has a stone foundation. At some point somebody decided it was a good idea to plaster Portland cement to cover the old stone foundation, which of course has been crumbling away since the day I moved in. I am currently in the process of removing all the Portland as well as the old mortar. Thankfully I found a local retailer who carries the Hydraulic Lime.

    For years I’ve worried about how I would ever restore our basement and all of your helpful information is much appreciated. I couldn’t agree more with regard to how closely guarded a secret this practice has become. A couple questions for you:

    1) How many bags of Hydraulic Lime did you need to complete your project? The stuff is expensive and I don’t want to purchase too much.

    2) Did you or have you considered any additional products to work as a sealing agent to ensure water and radon stay out? I’ve found some of these products (such as RadonSeal, which I find intriguing, but wonder if they are really necessary once you have gone through the process and the mortar has cured.

    Thank you again for such a wonderful reference for those of us in the same boat!


    • Kai

      Joe – thanks for your interest! So, lets see if I can recall the number of 55# bags. I know I bought far more than I ended up using because when it was all said and done I ended up selling five unopened bags on craigslist. [Pause] OK, according to our digital records I originally purchased a total of ten bags at CDN$54.95/each plus Quebec tax (the total came to CDN$620). I ended up selling the five unused/excess bags for US$30-35/each. Now, keeping in mind that I used cement based mortar when I re-pointed the interior face of the foundation (a job I finished more than a year prior to the start of the exterior work), five bags of NHL 3.5 for the exterior portion was the perfect amount. In the end, I was left with ~half a bag to spare.

      I can’t remember how I arrived at the number of bags but I clearly over-estimated by factor of 2. I do know that the approximate square footage figure that I used for my estimate calculation was 200sqft, if that helps at all. So, in the end, the exterior portion of the job ended up costing us ~US$600 including the price of the locally sourced (bulk) masonry sand. Had my estimate been more accurate (and/or had I been able to return unneeded bags for a full refund) it would have been more like ~US$375. I like to think that the extra ~$225 was the fee I charged myself for teaching myself the craft. 🙂

      In comparison, I used Lehigh-Hanson “Ironclad Type N Light Masonry Cement” and locally sourced (bulk) masonry sand for the interior work – walls necessitating either nothing or only light re-pointing or in several sections complete rebuilding – which cost us approximately US$250 in tools and materials (tools that I later used on the exterior work). In contrast, the interior work was way more involved but even so the entire foundation job (inside and out) cost us maybe US$850 – not bad in the large scheme of things.

      As for my labor, I didn’t keep track of my total hours but if I remember correctly it was weeks of work; by this I mean 8 or more hours at a time over the equivalent of three or four weeks. Something like that.

      Hope this helps!

  • gretchen maurer

    It is so wonderful to find this information! We close on an old 1910 Grange hall building in CT this week which we are turning into a private home for ourselves. I feel so much better having this information before trying to find a mason or tackling it ourselves. My husband already planed on doing the gravel as you did around the edges, as well as gutters. He was worried about excavating the dirt around the home but your steps give me reassurance in doing so with wisdom. I will be sure to pay attention to our rocks and their edges and strength which are under layers of something white..paint maybe… and crumbling that white powder….to see what matter of re-pointing we should do. Also someone mentioned starting inside first due to the season. We are closing in September so starting inside might be good for us as well. We do need to do some repair of timber rot at the sill plates that has been weakened under snow and near soil. Should we re-point the stone first? or repair the wood?

    • Kai

      Gretchen – Very glad the you found this post useful! As for your question, it all depends on the level of rot, the condition of the foundation at the associated spots and whether or not you’ll need to perform any jacking to return the structure to level. If the foundation under the various rotten sections is stable (and the rotten sections are short) and the structure is sound (no jacking required) then its just a matter of cutting out the bad section of plate and replacing it in kind. If everything’s compromised (and/or the rot is extensive) than you’ll have to jack the section(s) that needs work (to temporarily support the structure), cut out the rotten wood, repair the foundation and then replace the section of rotten sill (then re-sheath, re-wrap, re-flash and re-side). Good luck! 🙂

  • Caleb

    I too have spent endless hours scouring books and websites and calling cement and mortar supply houses trying to find info about lime mortar.I even went as far as calling a historical preservation websites and the U.S. department of interiors, (who thought i was crazy). I live in northern Ohio by the way. After a lot of research I have found that modern bricklayers and or supply houses have no knowledge of this lost art form or mortar recipe. After combining info that i’ve gathered from several websites both American and European, i have found a recipe that seems to work. And i have even started to patch my stone foundation with success, thus far. I make my lime putty by buying dolomitic hydrated lime from the local feed mill(Town and Country coop in this area for $6). This lime is also used to harden soil for horse stalls.Just make sure its hydrated lime with calcium oxide(any other ag lime will not work) I take a 5 gallon bucket and pour the lime in while slowly mixing in small amounts of water, until the mix is similar in consistency to cream cheese or drywall mud.I then take this mix that is in the 5 gallon bucket and pour about an inch of water over the top and seal it off with a lid. I then let this sit for at least a week with the lid on…(the longer the better). Now that you have your lime putty created for relatively little money its time to make the mortar. I used fine grain sand or play sand and mixed it in an old quickrete container. So far the mix i have found to work well is 2.5 parts sand to 1 part lime putty. I used an old coffee can for my parts measuring. mix this recipe together well only adding water if necessary a little at a time. You will have to chop and fold the mix several times before its ready. The mix will be thick and sandy but now your ready for properly pointing your old stone foundation.

  • Bo

    Kai –
    I live in MN and have a large limestone basement that is failing. We have easy access to the 7 ft walls on the inside, but how far down did you dig below grade on the outside to expose the walls to make repairs?

    • Kai

      Bo – Good question. I only excavated a couple of feet below grade on the exterior perimeter of our foundation (as evidenced by the photos that accompany my post) but that was plenty in our case. The design of our foundation, however, relies on an interior sand berm or buttress that’s held in place by multiple layers of skim coat (and now a layer of blockbond too). The foundation wall itself extends to only a few feet below grade – functional in our immediate area because of our predominate soil-type (sandy loam) – while the basement floor sits several feet below that. From what I can tell, the job of the perimeter buttress is to prevent the earth underneath the foundation from backfilling into the basement (thus ensuring that the foundation wall stays in place) and to prevent moisture from entering the basement. The latter is possibly assisted by the fact that the sand used to build the buttress appears to have been mixed with oil which (and again I’m speculating here) may have been done to impart a hydrophobic quality to the sand. Of course, it could also have done to improve the ability of the sand to hold the shape of the berm prior to its being covered in the aforementioned skim coats.

      The soil in our immediate area drains beautifully (and is so easy to dig!) and the land naturally slopes away from the building which also contributes to the basement remaining totally dry. We further improved the situation by installing gutters that act to drain every roof overhead and divert all roof-collected rainwater away from the foundation.

      In your case, however, given the height of the walls that you are dealing with (and the absence, it sounds like, of any sort of retention wall like our buttress) I would perhaps dig deeper. But that said, if the wall is otherwise sound on the interior there may be no need to do so. But your use of the words “failing” and “repairs” makes me think that your situation is quite evolved. If so, then I would consult with several different respected masons in your area to determine the best course of action. As I explained in an earlier reply, it may be that you will need to take steps to support the building (using beams and jacks) separate from the foundation such that you can then excavate the entire exterior face of the wall and make your repairs to the entire wall (inside and out) all at once. Also, in our case (and as I have described elsewhere in my other replies) the existence of two clearly defined and redundant layers of stonewall (basically an interior wall and an exterior wall) also assisted my work. I was able to make repairs to narrow sections of interior wall because I wasn’t doing anything to disturb or compromise the outermost wall (and vice versa). In other words, since the “two walls” as I am calling them were not tied together I was not limited in the repair work that I could do having not unloaded the wall (i.e. jacked the house); at least one wall was supporting the structure at all times.

      I wish you good luck on your project! 🙂

  • Tom

    I have been researching this topic for a while, and decided to use NHL 3.5 with a 2.5:1 Sand/Lime mixture, similar to what others have expressed works well. We have a 100+ year old home in RI with a fieldstone foundation in the basement up to about a foot or so below grade, and then brick to a couple feet above grade. Fortunately We don’t have any water infiltration issues – it’s just that the mortar has disintegrated and falls to the floor in the basement.

    The question I have is about the size of the voids in the fieldstone foundation. After removing loose material some of the voids deep in the foundation are pretty large. (> 4-5 inches) So, to fill this I’m planning to use a combination of mason’s sand and slightly larger gravel in my mix. Are there any issues doing so? Also, if I can find fieldstones that would fit some of those voids are there any issues using them, or should I just try to pack in as much of the mortar mix as possible?

    Thank you all for the discussion and comments.


    • Kai

      Tom – I’d say that you’re definitely on the right track. It all comes down to how much money do you want to spend on mortar and how much time do you want to dedicate to mixing. If the world was full of free NHL 3.5 and free labor to mix it then, by all means, we’d fill every void with just mortar mix (meaning no rocks or stones, a.k.a. no “aggregate”). But the reality is that aggregate is cheap (if not totally free) and plentiful and it helps to hold wet mortar together, especially in large voids, by increasing the surface area that the mortar has to bind to. So, in situations like you’ve described, its very appropriate to utilize additional rubble to augment you’re mix. Its much easier and requires much less mortar to fill even a small void with using both mortar and rocks (or broken concrete even just as an example) then to only use mortar. But I’d caution against mixing aggregate in with the mortar. You’ll need to keep them separate, otherwise, you’ll end up with a a mess on your hands. When encountering a void simply throw some mortar in first (as a bed) and then add your stone (or stones), using mortar to fill in the spaces around the sides.

      So, yes, infill is good. In my case, I set aside whatever rocks and stones I came across while excavating/rebuilding and used these to reinforce the wall whenever the need arose (which was often). I don’t know what law is at work in masonry restoration but it seemed that I always ended up with more aggregate left over than I started with. It all depends on the quality of the work that you’re essentially going back over. If its rough than your’re going to find yourself needing to add in a lot of additional rubble whereas if its of super quality then not so much. Chances are your wall falls somewhere in the middle of the spectrum that’s defined on one end by a wall thrown together and on the other by a mortarless wall from the Inca civilization. Its actually nice if you have the opportunity to add in your own stones since then you can point to those particular elements later and say to yourself “I did that!” Good luck! 🙂

  • Just wanted to thank you for your post. I just started a repair project in my basement, where the previous owner knocked out stone from the floor joists, down about 12″ and 3′ long, for plumbing he had to get through wall.

    I replaced the missing section with cement (since it is sitting on top of the limestone I’m hoping it won’t be a problem down the road) and was ready to repair some joints in the entire basement with cement when it dawned on me to do some research.

    Keep in mind that, to me, it looked like the builders (pre-1900) just used some mud mix. I had no clue that this stuff was mixed with a special lime to a set ratio.

    Your post and the comments from others has probably saved me from misery in the future. Luckily the supplier of NHL, Limeworks, is only about 40 minutes from my home.

  • Tin

    What do you think about this hydrated lime by oldcastle being sold at home depot
    50 lb. Type S Hydrated Mason Lime?

    • Kai

      Tin – a quick google search turns up this informative page: 🙂

    • Stu

      Tin – How did you make out with the Minuteman Type S Hydrated Lime purchased at HomeDepot? I am in eastern Massachusetts, but found some at a HD out in the western part of the state. Maybe worth the ride!?

      Kai – Great site. Thanks for sharing experiences both good and less good. Question for you…why did you do the interior of your foundation with standard cement? Did I read that right?

      I have a fieldstone (they call it rubblestone on T.O.H.?) basement under my 1874 Greek Revival. Faulty gutters, since fixed, used to lead to sand washing down into and through the fieldstone foundation. A few stones lie on the basement floor. I need to chisel out somebody’s poor cement patchworks and re-grout. I, too, am puzzled that the This Old House gang went with OPC + Krystol waterproofing. (Arlington House, Season 33 Ep 12) All my research says we fieldstone owners are better off with a wall that can breathe and expand a bit. And won’t chew away at the stone.

      • Kai

        Stu – You are correct, I repointed the interior with standard Type N masonry cement. The reason behind my doing so was simply timing; I started with the interior and hadn’t yet heard of lime mortar. Had I, I would have used lime inside and out. 🙂

      • Stu

        As follow-up to my note last autumn:

        I finished 20feet of fieldstone wall repointing in early April. Man! What a project. I attacked about 2-3 foot sections (each roughly 6 feet tall) and worked on this in periodic spurts. 1. Tarp on floor, scraping out loose mortar and sand with a stone mason’s chisel and hammer. In many spots the ensuing holes (or negative space) after scraping were 8″-12″ deep, and went back to the outside dirt. I found a few very small old hairy roots and a bug or two, though this was not a problem. Attacking small sections let me test the standing integrity of the wall. I found the larger rocks and boulders held our old house up fine. 2. I hauled into the basement 80 lb bags of Type S Masonry Mix from a local Boston area quarry called “VitaCrete”. A premix of lime, sand, a little bonding agent. Threw 20 lbs at a time into a heavy plastic tray from Home Depot, and mixed with water, a pint at a time until I had a peanut butter consistency. A garden hoe helped. 3. I lifted a baseball size wad of wet mix on a mason’s trowel to the wall and jammed the mix in as deep and as hard packed as I could. Rubber dishwashing gloves really helped as I used fingers, thumbs, along with putty knives to jam the mortar in.
        Each section took a day or two to dry and harden.

        Between scraping & repacking, hauling heavy pails of old dust and new 89lb bags of new mortar, working in a tight basement for hours, and the slow go nature of the work, this was a beasr of an all winter project. However! I am quite pleased how it all looks and functions today. No more leaking sand or wet spots on floor. The ugly rusted and cracked and dusty mortar joints all look clean, strong and intact. The basement wakl looks so good I threw up LED track lights to show off our fancy new “Rathskellar”!

        Tip1: Find a mason’s yard/store where lical masons and landscapers go for stone, pavers and such. Invest in good hammer, chisels, trowels. Ask questions! My project cost was about $120 for tools, taroa, buckets plus about $100 for bags of mortar. Get 2-3 plastic 5 gallon buckets for sand removal, water hauling, I also bought half a bucket of small granite rocks to add to larger gaps in the wall.

  • tatyana


    Thank you for you site, we have 120 years old house with granite foundation, that needs a lot of work, which we are planning on doing nest year, but while replacing our stairs we exposed the corner that I believe needs to be fixed ASAP. We are located in NW and rain season started already. Do you think it is ok to just cover with tarp and let it cure?


    • Kai

      Tatyana – I’m a little confused by your comment. What exactly are you referring to in relation to your question? If you think the corner needs immediate repair then assuming you’re in a part of the world where temps don’t drop below zero (or you’re willing to cocoon and heat the area that need works) then I’d go ahead and perform the repair. But if you’re asking if you should just tarp the stairs (which is what it sounds like you’ve already repaired) and leave the questionable corner until dry season then I’d respond by saying that you should do what you think is best and/or consult with a qualified mason to assist you in your decision. Also, did you exact the repair to the stairs with lime or masonry cement or concrete (or something else)? If you used lime then you’ll need to follow the curing steps related to the specific product that you used. In some cases you may need to ensure that the masonry is kept damp throughout the curing period. But again I’m unclear what the corner has to do with the stairs, what the stairs are constructed from, and what action (or inaction) exactly you’re considering taking in relation to all of the above. Perhaps you can provide some more info. Thanks. 🙂

    • Kai

      Tatyana – I apologize but I am a little confused by your comment. What exactly are you referring to in relation to your question? If you think the corner needs immediate repair then assuming you’re in a part of the world where temps don’t drop below zero (or you’re willing to cocoon and heat the area that need works) then I’d go ahead and perform the repair. But if you’re asking if you should just tarp the stairs (which is what it sounds like you’ve already repaired) and leave the questionable corner until dry season then I’d respond by saying that you should do what you think is best and/or consult with a qualified mason to assist you in your decision. Also, did you exact the repair to the stairs with lime or masonry cement or concrete (or something else)? If you used lime then you’ll need to follow the curing steps related to the specific product that you used. In some cases you may need to ensure that the masonry is kept damp throughout the curing period. But again I’m unclear what the corner has to do with the stairs, what the stairs are constructed from, and what action (or inaction) exactly you’re considering taking in relation to all of the above. Perhaps you can provide some more info? Thanks. 🙂

  • Gillian

    Hi Kai, I have been doing my research about the benefits of using Lime since I have to re-point my basement walls and I read that Lime mortar can accommodate considerable amounts of movement without cracking due to creep (continual strain under constant stress), whereas more modern walls require the frequent provision of movement-joints. Since my building is over 100 years old, there has been settlement and because I am so close to the road, there is vibration transferred from the buses and cars. You mentioned that you used “Ironclad Type N Light Masonry Cement” for the interior of the basement. I am just curious why you did not use lime inside your basement since it would be more breathable and can wick away moisture from the wall?


    • Kai

      Gillian – Good question. The simple answer is that I re-pointed the interior first and didn’t learn of lime mortar until long after that portion of the project was complete (the two phases of the project were separated by a couple of years from start to finish). Had I known then what I knew when I tackled the exterior I would have happily utilized NHL 3.5 on the interior as well. Good luck with your project!

  • Hugh

    Hi all, nice to see Lime is seeing a revival on the other side of the Pond. The revival in Lime is well established in the UK, and its easy to find material, and instruction courses that allow you to practice before you start your own project. The original courses were pioneered by SPAB (Society for the Protection of Ancient Buildings) . Below are some more Links to UK sites that offer advice on the use of Lime:-

    I have only a couple of things to add advice wise:

    Wet the stonework before starting work.
    Start from the top and work down.
    Keep your mortar mix on the dry side so it doesnt slop all over the stone work.
    Use ‘sharp sand’ ie sand with tiny stones/grit (about the size of buckshot) in it. Soft (Builders sand) can lead to cracking as the mortar dries out.
    If its hot, drape damp hessian cloths or old sheets over your work to stop it drying too quickly, and keep them wet. (cracks again).
    Once the mortar is firm to the touch ‘Bag it’ to acheive a smooth finish – ie ball an old piece of hessian or other course cloth, and rub the mortar joints with it. This will give you a smooth surface, and leave and pieces of grit in the mortar with a shiny surface. You can also use a brush for a coarser finish. Stubborn bits of mortar on the surface of the stone can be removed with a wire brush.

    If you have trouble with damp coming through the walls, check the outside ground level. (This was a tip from my Building Conservation Officer) Open a window, put a long peice of wood through it and level it with a spirit level; then measure the distance to your inside floor level and the outside ground level. If the ground level is above floor level (often happens with the passage of time), either lower the ground level, or dig a trench and fill it with rocks (we call this a French Drain in England). When I followed this advice I removed a concrete path, dug down a bit further and found the original path (below floor level) that was made of stone slates laid on their edge – and an old Well too! It also cured the damp problem.

  • Joey

    Thanks for this discussion. In the same boat as everyone else. Real quick, I’ve asked several contractors for estimates to repoint my 1910 sandstone foundation in Idaho (mountain desert). Every contractor says my foundation is still in great repair and have placed bids for the repoint. I have asked what joint compound they would use and their answers have all been either Portland Cement with 50% lime, or 60% portland cement / 10% lime / 30% Masonry sand. Have you or anyone on this feed found a mixture to be sufficient or is it only the limestone sand ratio you described that is found to be acceptable. Several of these contractors have over 50 years of experience in the historic area of Boise where my house resides between them and their dad. I feel they should know a thing or two about this option for this area, but want to hear if others in this forum know something they do not, or have experience to say they are definitely wrong in their approach. I’m definitely looking to contract, so need a contractor in my area and after six bids (three of which were referrals from the area’s main commercial masonry supply store), want to just sela the deal and get the work done this late spring / early Summer.

    I appreciate any constructive advice!


  • Dave

    I have been researching lime mortar for the past year because we purchased an old farmhouse a little over three years ago and are in the process of renovating the whole house and property. Your article really explains the importance of lime mortar very well. We are currently in the process of redoing the basement. The foundation walls are old fieldstone foundation walls that are roughly three feet wide and the basement is dry and there are no water issues at all. The only problem is with humidity. The previous owners all painted the walls different colors. I think with each owner over the years came a different color of paint. I spent the last eight months taking the paint off the walls and I was left with no other option than to use a chipping hammer. I had tried various paint removers with no effect whatsoever and to sand blast was definitely not an option so I simply used a sharp chisel on the end of a small chipping hammer and peeled off the paint from the wall. Many, many , many hours but seemed to work well. Some places the paint had locked the moisture in and thus the mortar was breaking loose from the wall. I would now like to put a new coat of plaster on the walls to make them look nice and was wondering if you have any suggestions regarding this as far as a product that is available. I would really like to hire a local mason for the job but they all say they will use a premixed quickrete product that is cement based and I really think it is important for the old walls to be able to breathe. Do you have any suggestions?

    • Kai

      Dave – thanks for throwing your question out there. Having never done any real plastering myself (I’ve tended to reach for Durabond to date when repairing plaster walls) I’d suggest getting in touch with one of the lime retailers mentioned above and/or a contractor who specializes in plastering. I know I look forward to experimenting with plaster in the future so I wish you luck on your plastering own job.

  • Shelly

    Dave, I use Imperial brand(or another brand, whatever is available) “Veneer Finish” plaster, bought by the 50 pound bag. I have done plaster for years, and it takes a while to get your hand in and do it properly. I have done whole walls, 2 base coats, which is a different product, and a veneer coat or “finish coat”. You will need a drill and a mixing tool, a hawk to work from while you use a trowel to put it on the wall. The mixing ratio is 4 parts dry to 1 part cold water. You must work fast with the veneer plaster before it’s too hard to work. This requires some practice work. Any loose or disintegrating base coat must be removed and replaced. If you hit the wall with your hand and it moves, it has become un-keyed from the lath and must be removed and then re-plastered. My plaster work is holding up like a dream after years. It is fun but a lot of work! There are many Youtube videos available to see plastering demonstrated.

  • Joey

    Any feedback on whether 50% lime with 50% Portland cement would give the joint compound the flexibility it needs to remain a strong pointing compound? It’s done around my part of the country and just want to see if anyone knows this to be a proper solution to this issue of sandstone wear and tear. I appreciate all feedback and hope to hear from a knowledgeable source.



  • Thierry

    Hi all.
    i leave in the UK and just bought a 1900 house and some of the bricks have spalled due to the use of cement by the previous owner. I am new to lime mortar and hopefully will do as good as yourself Kai.

  • Jon

    I have found that the website and Lancaster Lime Works is full of information regarding all things lime mortar related. It is a small course on historic mortars.

  • Chholing

    Great blog and questions everyone. As I need to tuckpoint my stone wall in a 1867 home. I was able to track down a distributor here in MN in the even you have some mid-west readers. They carry LaFarge type N!!

    Marshall Concrete
    2610 Marshall St NE
    Minneapolis, MN 55418
    (612)789-4305 • (612) 789-5387 Fax

  • Patty

    Recipe from Old House Journal Compendium: mix one part portland cement with 3 parts hydrated lime by volume. Add 3 to 5 parts by volume of sand to one part of the cement-lime mixture. we are going to try this on our fieldstone foundation circa 1880.

  • Dave

    I have a pre-1900 fieldstone house. The walls are 18 inches wide. I’m glad I found this artical because I’ve been getting the wrong information. I need to do some patching inside and out around the foundation but my question is can I use this mortar around the whole house? Exampe being there have been a couple areas above the windows which have been filled with portland cement and it looks like it wants to pop out. So basically I’m just wondering if there would be a diferent consistancy for above grade.

  • Peter Ottenhof

    I have a 100 year old lime mortar/limestone-rubble foundation that is shedding its parging inside and out. Some opinions have it that the whole foundation has failed and needs to replaced/supplanted. There is tho, very little evidence of general failure either as sagging or large scale movement of the cinderblock walls. As I brush and vacuum the foundation to remove that which has turned to dust, I come to mortar that is modestly stable but not strong enuf to be vigourously worked applying new mortar (or concrete for deeper voids). I try very hard not to disturb the limestone chunks. I’ve been “stabilizing” the old mortar with Quickcrete Concrete Bonding Adhesive sprayed on with an airgun for good penetration and coverage. It makes a big difference in the perceived soundness of what I’m working on. Now I’ve learned about the incompatibility between lime mortar and OPC and I’m wondering if there’s a better product than the Bonding Adhesive to strengthen and prepare the mortar for another 50 years of good service.

    Thanks for the site

  • HI KAI


  • sunil yadav

    Hi,i have one question . if u know plz send my mail. my question is ,which one is good for foundation stone masonary or reinforced concrete? there is one story building and four email id is

  • Ping

    Hello Kai,

    Stumbled across your site while looking for ways to fill up huge gaps in a stone wall which had developed after years of being covered up inappropriately behind gypsum. I’m in England so materials should be available very easily. However I wanted to thank you for such a detailed entry – your enthusiasm is inspiring! I have a feeling I’ll be learning much just looking through the comments section.

  • Carl

    Hi Kai,
    This is probably the best write-up I have found about the importance of using a lime-based mortar instead of just a concrete-based mix that most masons I have called want to use.
    I have an 1889 home in the Boston suburbs with a fieldstone foundation and a partial dirt floor basement. I want to pour a concrete floor and seal the walls to make the basement drier and less dusty for storage. The basement doesn’t get water but gets damp in the humid Boston summers. The foundation is in OK shape but in a few spots the old mortar has turned back to sand – the same spots that get damp.
    Rather than repointing, I am considering covering the walls in a rubber membrane to seal them. I realize this isn’t a best practice buts about 1/10th the cost. Any idea what risks I run by not repointing, sealing the wall, and not allowing the old lime-based mortar to breath? I worry about covering a potential future problem – the structural integrity of the foundation.

  • Carl Sciuk

    If my stone foundation is 2′ thick, and my structural load is on the outside half of the wall, can I just repoint from the outside and try to remove and repoint the outer 1′ of wall thickness? The inner wall is covered with drywall and I would prefer not to touch it if I don’t have to. Do you normally try to repoint right to the very middle of the wall from both inside and outside?

  • I have a dutch colonial single built in 1927. I am having a problem with my fieldstone foundation exterior. it was originally pointed with a raised beaded mortar joints. the raised beaded joints started falling off first, then the mortar on some stones cracked and others fell out completely exterior. I am having an insect problem as some of the gaps are pretty deep. it was patched over the years with different materials colors etc. none of the stones are loose. we enclosed the front porch the enclosed fieldstone wall was originally an outside wall, the mortar on this is not falling out just the raised beaded joints are falling off. I can’t afford a total restoration job! how should we proceed , I’m not able to take all the mortar out and start over. I know I have to chip out all the loose mortar, what tools and materials should I use to keep insects and furtur decline of the exterior. inside porch wall is another story that hasn’t been patched or touched at all since the house was built, should I send a test sample of mortar so I can patch raised beaded joints falling out and some minor holes where the raised beaded joints fell out??? any help would be gratefully appreciated! thank you all.

  • The reason I found your article is that so much mortar has fallen out of my basement foundation walls, that piles of sand are accumulating on the floor. And when I reach in to clean out the loose mortar, the void gets deeper and deeper!

    Thank you so much for taking the time to explain this. I have an 1860’s brick house- triple thick with plaster directly on the outside walls. It’s the really soft bricks, no patina to them, and sand is falling out from between them on the outside as well.
    I totally get the needing to breathe.

    What people around here do is to have them repointed with cement and then coat the exterior with silicone ‘to keep the water out.’ I have been having my brick repointed in places where it’s bad,but I have let the cellar go.

    I cemented the cellar when I bought the house, and I have to use a dehumidifier or water bubbles up and forms on the floor. So the dehumidifier is killing the mortar joints? I don’t know where to go from here– the reason I looked up “lime mortar old houses” was to see if I could just dump the loose sand in the cellar, out in the yard, if it was toxic or not. Now from what you say, I am thinking I should save it and use it to repoint the stones?

  • bill

    Great Read! Thanks Kai:

    I’m curious why you went for NHL 3.5 over NHL 5 which would be stronger and possibly better suited for foundations while still maintaining the breathability of historic lime mixes. Also the mix of 1:2.5 seems high for sand content, as historic buildings tended to originally use 1:3 (using quicklime of the day) which translates to roughly 1:1.5 to 1:2 (depending on the application) using hydrated lime. Then again you did perhaps compensate for this it seems by using NHL 3.5.

    A lot of variables and all very confusing.

    Here’s a good site about historic mortar usage.

    • Kai

      If I recall correctly, there was more info available regarding 3.5 than 5. Also, I think I thought that 3.5 was a vast improvement over the original weak lime and since it was plenty sturdy enough to outlast me, why use 5? Cost may have also been a factor (maybe 5 was more expensive than 3.5?). Thanks for your question!

  • Dave


    Just wondering how your repointing work has held up over the years since you started this blog. Any degradation or for nation issues? Would you do anything different if you had to do it again, or are you still really happy with the job? I am about to start repointing my 1900 sandstone foundation on my 40×80 dairy barn in Ohio, and am thinking of using NHL 3.5 mix. Thanks for such a great post. -Dave

  • Amber

    This information was exactly what I needed. Just to clarify, you ended up using ~5 bags for ~200 sq. ft., correct? About how much masonry sand did you end up using?

    • Kai

      Amber – I used a ratio of three to one (sand to lime). I just picked what I thought would be enough (a small pile that I tarped to keep it dry). I collected it in bulk and paid nothing for it so….

  • I live in Gloucester, MA, repointing a granite fieldstone foundation from late 1800s…

    Where is the cheapest source for NHL 3.5 in US? I found this company (.72/lb), but would love to hear others sources:

  • Scott Clydesdale

    Hi Kai,
    I have an update and 2 questions.
    There is an NHL supplier just outside of Toronto, ON in Woodbridge. They also have Processed NHL that has sand added, e.g. XHN-60. Read the data sheets for various products on the Daubois website:
    click products>click DIVISION 4>click product of interest

    the Woodbridge supplier:

    Blok-Lok Ltd.
    12 Ashbridge Circle
    Woodbridge, ON

    There is also a book available on Amazon that I am ordering:

    Hydraulic Lime Mortar for Stones, Brick and Block Masonry: A Best Practice Guide (2015)
    Author: Geoffrey Allen

    Kai, your text mentioned that your stone mason contact said…”use masonry sand and add some larger aggregate for filling larger joints.” Was this aggregate washed gravel, or limestone screenings, or…?

    Also was wondering if you mixed less than one bag at a time?

    Thanks so much for maintaining trhis site

    • Kai

      Scott – Thanks so much for including the details about your local supplier and also for including mention of the fact that there is a sand-added product – very interesting. I wonder if the latter is a nod to the burgeoning sharp sand crises that many localized regions are facing:

      Regarding your two questions, it is common to use small pebbles or stones (of any kind) as a filler when faced with a) large gaps and/or b) when trying to stretch out a supply of mortar. Also, stones inserted in a finished bead are sometimes used a decorative touch (which, by extension, also reduces the amount of mortar used).

      As for whether I mixed entire bags at a time, absolutely not. I used a paddle, driven by my 1/2″ electric drill, and a 5-gallon bucket to mix small batches. This produced much more manageable volumes of mortar and the bucket (with bale) made moving it around a simple matter.

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