Making Your Own Hydraulic Lime on the Cheap! –

Written by Andrew Morrison

lime plaster
Here’s a recipe for making your own hydraulic lime on the cheap. Ever wanted to use hydraulic lime but not been able to find it in your area? Or perhaps you can find it, but it is going to cost you more than the rest of the house combined to ship it to your location. Have hope, there is a way to produce your own hydraulic lime from a much cheaper and more readily available source: quick lime and brick dust.

hands in sandSimply add up to 5% brick dust to your quick lime and voila, you have a lime with similar properties to hydraulic lime. To be clear, it is not hydraulic lime, per se, but it behaves in much the same ways. This is considerably cheaper and the ingredients are available in most areas.


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46 Responses

  1. Hi there, what is the difference between type s lime and hydraulic lime? Is one type better for plastering of straw bale or cob?

  2. In your article about making “Your own Hydraulic Lime on The Cheap” you referred to Quick Lime and adding 5% brick dust to it. My question is, what is quick lime ? Is that something that I can buy at Home Depot ot Lowes ?
    Tim ([email protected])

  3. Hi Andrew, I am disgusted. Where does this recipe all of a sudden comes from. Since June I am trying to get a formula to make my own NHL. I am sure you will remember all me e mails crying out for help from you or anybody else who can help with the producing of my own NHL. The main reason of course is that all countries don’t manufacture NHL. Except for one guy who came up with the mix of a pozzolanic material with lime that will bring you close to NHL, nobody else came forward. Surely you must have known that brick dust can be used. I even tried for help at saint astier. It gives me the idea that the recipe is actually well known but not available to everybody. After buying your dvds and studied them I understood the importance of using NHL. Obvious I could not import NHL. The next step for me was to make a in depth study of NHL. I ended up with a product that also harden under water. The problem is how do I test my product. Will it allow breathing. Except for the under water test I had no guarantee. Is there any other way to test the NHL. I could not take the risk with lots of expenses without a guarantee that the correct plaster is used. The plaster is the most important part of the whole construction. So I let go of the project.
    Do you add any sand to the brick dust and lime. If you do, I would like you to give us a better formulation like for example 1 sand, 5 b/dust and 8 lime. a Lot of people knew I was busy with experiments on the NHL and I am pretty sure they will be very pleased. The fact that we can not get NHL in Africa had a very bad and negative influence on Strawbale building. Your latest information on the NHL will help a lot but it need to be more specific. What about the other pozzolans.

  4. Thanks for all your comments. I can see this is an interesting topic for many of you. Please forgive me for any lack of clarity. This is a new piece of information for me and I am still researching and discussing the details of it. What I know is that it most definitely can be used on the interior and the exterior of a straw bale home when mixed properly. A basic mix for a scratch coat is 1 part lime putty (I’ll get to this in a minute) to 2 1/2 parts sand by volume. Add 4-5% brick dust by volume when you are ready to make the final mix of plaster. In other words, when you add the sand. The brick dust should be available at plaster supply yards or rock landscaping yards. It is not likely something you’ll find at Home Depot or the like.

    Type N and Type S limes are both hydrated limes and are usually available at Home Depot and such stores and most definitely available at plaster supply yards. The difference is in the purity. Type S hydrated limes have been slaked more completely which ensures that any magnesium oxide in the material has been slaked fully. The dry, powder hydrate, most typically the form in which it is sold, can be used right out of the bag; however, it is best to slake it for a while in the form of a lime putty before use if you have the time and ability (More on Lime Putty in a minute)

    Type N is only partially hydrated and as such may still have un-slaked magnesium oxide in the material. For this reason, it must be slaked for a longer period of time before it can be used.

    To slake hydrated lime, you must add the powder to water. NEVER add water to the lime, only add the lime to water. If you do this backwards, the chemical reaction that takes place can happen too quickly and the mix can explode. Be sure to wear goggles, a mask, and skin protection during this process.

    By adding the mix to the water, you are “slaking” it or rehydrating the mix. During the original processing of the material, all of the water was driven off during a heating process in which the raw material was heated to roughly 2200 degrees Fahrenheit (1200 degrees Celsius). The water now taken in changes the chemical makeup of the material. The longer you leave the lime submerged the better the slaking job. When you are done and ready to use the material, it is called lime putty (Calcium Hydroxide).

    Do not expose the material to air once it has been rehydrated as it will start to harden and, once again, change its chemical makeup. In line with this, don’t add the brick dust until you are ready to make your actual plaster by adding the sand. If you add the sand and/or brick dust during the slaking process, the plaster will harden, even under the water. This is one of the properties of hydraulic lime, the ability to harden to under water.

    I think that has answered all the questions above. Keep in mind that as you go out from scratch coat to finish coat, you want the plaster to get weaker. I know that sounds strange, but it’s true. You want to add more sand to the mix as you go further from the substrate. In line with that, you would have mixing ratios of:

    1 lime to 2 1/2 sand plus 5% brick dust for the scratch
    1 lime to 3 sand plus 5% brick dust for the brown
    1 lime to 3 1/2 sand plus 5% brick dust for the finish

    Be consistent in your measurements of all materials. Even slight variations can cause problems in the plaster. All measurements are by volume, not weight.

  5. Dear Andrew,

    It’s been a year! We took your course in NY last fall– time does fly. Due to family and business issues we had to address first, we are still getting our loan. But we’ll get there…

    One issue you may still be working on is a performance comparison between NHL and quick lime + brick dust. Any comments? Also, can you guesstimate how much cheaper this new mix is compared to NHL (without transportation costs considered, which will vary widely)? Is it 1/2 the cost? 1/3? This is important to know in balancing the money saved vs. the risk of a subpar finished product (in the sense that this new mix hasn’t been weather tested over many years).

    Ted T.

  6. Okay, so which type of lime are you using? Is one more suitable than the other for different applications? Which would you reccomend for straw bale? I live in British Columbia Canada.

  7. Hi All,
    I thought it would be worth mentioning that you can’t make your own NHL because the ‘N’ stands for Natural. Basically, the limestone used for making the building lime has a quantity of clay found ‘Naturally’ in the limestone. The clay is the part which makes the lime hydraulic. To make this even more complicated it then depends on how much clay there is (eg, 5%, 10%, 20% etc) as to how strong it will be (eg, 2, 3.5 or 5 Kilo Newtons) The next problem you have is the subsequent crushing strength after it has set, because at the top end NHL5 can set up to 15-20 Newtons over time. For those of you who are new to the European standards, what this means is: if you use a high strength Hydraulic lime you could end up with a product nearly as hard as cement! Another point to remember is that the sand you use is as important as the lime itself; it must be sharp with equal parts of each aggregate size eg, 1mm, 2mm, 3mm, 4mm, 5mm. It must also be washed clean and the shape of each particle jagged and sharp. Sorry if this all sounds complicated but it is important to the success of the finished product. Remember that what you are trying to achieve is flexibility and breathability; when using NHL you are compromising on flexibility. My advice would be stick to lime putty and a good sharp sand if you are unsure of what you are doing. Lime work can be extremely complicated, try and keep it simple: 3 sand to 1 lime putty with LOTS of hair or fibres included.

  8. Thanks Andrew, This is going to make a very big difference. Some friends already phoned me. According to some of the guys (big and heavy glasses with white over coats)Fly ash would be the better choice as a pozzolan which is also easily available but I don’t know what the formula should be. Maybe we can experiment with that also.

  9. “Quick Lime”, as was said, is made by heating Calcium Carbonate rock powder (lime stone, ancient sedimentary calcium deposits from pre-historic sea beds) heated to an extreme temparture (1200C). CaCO2 –> CaHO –> CaO as increasing heat is applied. Quicklime is CaO (Calcium Oxide).

    CaO will pull water and carbon dioxide out of the air pretty rapidly and will eventually retransition from CaO –> CaHO –> CaCO2.

    Keeping CaHO in the water it is slaked into excludes the carbon dioxide, so the transition goes from CaO to CaHO and holds there for a while till removed from the water, when it transitions to CaCO2, hardening and becoming “lime stone” again.

  10. First of all I appreciate this website and the interesting subjects discussed here.

    As Andrew mentioned there are different types of lime (actually 3 basic ones)

    1 Dolomitic Double Hydrated Lime (type s) Ca(OH)2
    2 Calcitic Hydrated Lime (type n) Ca(OH)2
    3 QuickLIme (lump lime) (CaO)

    Without going into too much detail limes 1,2 are pre-hydrated and are readily available at Home Depot, Lowes or a building supply house.

    However this article recommends Quicklime. Quicklime is harder to locate here in the US. Additionally this product is the one that gets hot when added to water. If you purchase it in putty form it needs to have rested for at least 3 months to be used as a “render”.

    The experiments I have performed have been with Type S lime and brick dust. However I have not performed experiments with Quicklime which is more reactive. I am guessing that the pozzolonic reaction is stronger with the Quicklime… I don’t know.

    However a test consisting of 1 part type s lime to 4% brick dust was performed by two Greek civil engineers I. Papayianni and St. Konopissi at the 2005 International Building Lime Symposium.

    This test yeilded a compresive strength of 122 psi after 28 days and 211 psi after 90 days (does not say what proportion of sand).

    Compare these numbers with the 194 psi after 28 days and 571 after 6 mos for the NHL 3.5 mixed 1:3 with sand and you are not comparing apples to apples.

    I have done some experiments myself and there are other pozzolan options. It would be very interesting to get others results.

    Best Regards,

  11. Fly Ash may need to be analyzed for pollutants such as heavy metals (cadmium, lead mercury) and other (sulfur). China recently used this as additive to drywall and it has turned into a nightmare.

  12. Andrew, I have all the caliche I need right here on my 20 acres, and was wondering, since caliche is the principal raw material used for Portland Cement, what would be my mixing ratios? or would this even work? Thanks, Wade!

  13. Hi Andrew, thanks so much for trying to help us with an alternative to the NHL 3.5. I am trying to put this in sequence relative to what we did in Grants. Would we put the type s lime into the mortor mixer (after the water) and then pour it out and cover it? Then come back during the workshop put the putty back in the mixer and then add the sand and 5% brick dust? Would it need to rest again before platering again like we did in Grants?

  14. Hi Charles. As I understand it, you would slake the lime by mixing the lime into the water and then setting it aside (under water) for as long as you can. When ready to use it, you would mix the putty with the ratio of sand and brick dust. You could then leave that mix covered tightly for use within 6-12 hours like we did in Grants. You would not have to let it sit the second time, but it does make the plaster easier to work with and stronger in the end.

  15. Hi Wade. I’m going to have to defer that one to those people with more plastering expertise. That is not something I have experience with and so cannot give a good answer. Anyone else have a response?

  16. Andrew. What about Fly ash? Don’t you think one can get the same result even if it contains other heavy metal’s.I get the idea that the lime as a binder should be little more in the mix. Why cant you not mix the S lime, sand and brick dust at the same time and use it immediately as plaster

  17. Andrew,

    I wish to incorporate straw bale onto an existing ruin wall made of cemented rock and brick. Can I use the same type of plaster over this surface as I would my baled area? Looks like some type of cement facing then some white lime mixed was used on the stone area previously.
    All responses very welcomed!

  18. Yes you can Greg, just make sure you have adequate tooth for the plaster. You may need to use a wire mesh to give the plaster good anchoring over the stone and will certainly need to use plaster lath at the transition at the very least.

  19. Hi Andrew, I was wondering if I go the Type s plus brick dust etc. for our workshop, do I need to slake the lime prior to the beginning of the workshop or could we do it on the first or second day? How in the world would you keep in under water…..I am not willing to use the swimming pool or hot tub :]

  20. Hi Charles. The longer you can slake it the better. Also, I think it would throw a wrench in the time line to mess with slaking at the start of the workshop. I find that bath tubs and 55 gallon drums are where most people do their slaking. They mix in an old bath tub and then transport it to the drums where they cover the top with water and then seal the drum. You should probably check the drum weekly to make sure there’s still water on top since you live in a dry and hot area of the world.

  21. Thanks Andrew, This is great. I have been looking everywhere for hydraulic lime and can’t find any in my area.
    I am building a cob home; does anyone know if this would work for the exterior? Cob needs to be protected from the rain but the walls also have to be breathable so that no moisture is trapped in. I would like to start making some now so it has time to slake. Help would be very much appreciated!:)
    Thanks, Garrett

  22. Hi Garrett. It would work for you; however, the application of lime over earth is not easy. If the cob is not prepared properly, the lime can flake off of the wall as it separates from the substrate. Perhaps others can say more on this subject. If you need more information and it doesn’t show up here, let me know and I can say more (before you start plastering).

  23. Great topic! Here in Romania we found NHL to be very expensive, ten times more then the quicklime + brick dust solution. Thanks a lot, we’ll try that, Andrew.

  24. I am building a strawbale studio in my back yard and have decided to use hydrated s lime, sand, and brick dust for the plaster. The only problem is that I cannot find brick dust anywhere in Oregon and shipping it approaches the cost of NHL! Has anyone found a source for brick dust in or around Oregon?

  25. Hi Kathryn. I always use NHL, so I don’t have a source for you; however, I wanted to make sure you are aware that you can use other pozzolans than brick dust. You might try contacting your local cement companies to see if they have any suggestions. Some offer the use of fly ash in their mixes and thus may have something that would work on site. You can check out the wiki definition of pozzolans here: Good luck.

  26. Thanks Andrew, I decided to order brick dust from a company called sports advantage in Indiana. Fly ash made me nervous and I would still have to ship it. Even with the cost of shipping I will save nearly $1,000 on plaster so it’s worth it. I’ll update once I start plastering!

  27. Just wondering if I can use this make a tub. I’ve been wanting to make a tub out of earth and I’ve seen a few pictures online in earthships and Italy. The cisterns in ancient Judea were coated in hydraulic lime and I think they made tubs out of them too. The cisterns in Petra were also using it. Will this stuff perform the same way even if I have to re-coat it every so often?

  28. I have never done so, but I imagine it is possible. Hydraulic lime cures under water so that’s a good start! I would expect to have to add some type of water proofing to the lime though as I don’t know that even a well steel troweled finish would be water tight.

  29. We used NHL on the outside of our SB home and are getting ready to plaster the inside. We were going to use an earthen plaster due to the cost of NHL, but then I see this cheaper lime idea. The first comments are over 4 years old now. Is there more research/knowledge about using this method and if it holds up over time better indoors than an earthen plaster? If anyone has tried this method, how much did it end up costing and was it worth doing? thanks.

  30. Hi Sara. It works very well and holds up great. It’s not quite as good as true NHL, but it does work. On the interior, earth plaster is a great choice too. Just be sure that you thicken the earthen coat to more than what you have on the exterior. For example, 1.5″ lime on exterior = 2″ earth on interior. This balances the movement of moisture through the wall.

  31. Where do you find bulk brick dust? Also curious if any further experiments have been performed or if there is any updated statistical data regarding optimal mixture ratios.

  32. Hi Jon. I have not seen any additional testing on the ratios. IN terms of the brick dust, I would contact any brick manufacturers near you or look for other “pozzalon” materials available through plaster supply yards.

  33. Hi Andrew. Great article, and great site. What you are describing is a very ancient practice. It’s essentially what’s called Khorasan mortar, in the Middle East. In modern Turkey it’s called ‘Horasan Harci’. It’s great that you are popularizing it.

    As to different ratios, there’s some modern english-language academic papers on the material properties of old samples of the stuff, and different mixing practices. Also restoration contractors in Turkey are getting hip to the idea of using it instead of Portland cement in restoring older buildings.

    Maybe some good ideas can be gleaned from here, for example:

    Using brick dust as a pozzolanic ingredient to lime mortar, to impart hydraulic properties, actually predates the Western Roman use of volcanic pozzolana to make durable mortar and concrete. It was practiced through the Eastern Roman Empire, where Byzantine Greeks called this practice Korasani, It was also done in Sassanian Persia, and its use exploded under the Seljuq and later Ottoman Turks. But traces have also been found in Ancient Assyria and Egypt.

    This practice made its way to the North African Maghreb, and there are old buildings in Morocco and Algeria that were constructed with brick dust/lime mortar.

    The Ottomans used it not only as mortar and plaster, but also essentially as a concrete. Some old Jami Mosques and Public Baths in Turkey are constructed on thick foundation mats consisting of poured Horasan mortar.

    The ratio of brick dust varied and sometimes broken pottery shards were thrown in as aggregate, if it was being used as a structural concrete. Done right it can make very water resistant external renders/stucco and have a durability similar to ancient Roman concrete.

    I’m hoping that anyone reading this gets further inspired to further research Khorasan mortar and practical ways of using brick dust as a pozzolan.

  34. Hi. I recently watched a video on lime mortar where the builder used finely crushed charcoal instead of brick powder to make his hydrolic lime equivelent. Would this work ? I mean it is giving it a carbon source to pull from ?

  35. Hi William. The key is to create hydraulic properties by the addition of pozzolans. If you research pozzolans, you will see that many different materials can be used. Best of success to you.

  36. Hi, great article! I am planning on an hempcrete renovation and will need 70 cubic metter of it… witch add up to 10 to 15 tone of lime. The supplier i’m dealing with seem to only know NHL wich is really expensive in Canada. (like for the project 30 thousand more expensive)
    I’m surprised at how hard it is to find a good recipe for hempcrete with pozzolans and hydrated lime… Do you think the brick dust would work for 12inch hempcrete wall? Some of the people i follow used only hydrated lime… any tought on that?
    anyways, thanks for this article!

  37. Found a pretty decent research paper on comparing pozzolans (link below). Basically metakaolin is the way to go! Metakaolin is still kind of expensive (I seem to be finding 50 lbs. bags for around $45 online), but because of the final clay content in a mix, according to the NHL rating system, it may be possible to make a batch of AHL5 with 80% S-Type lime and 20% metakaolin. If anyone tries this out, let us all know. I’ll try to do some tests myself as well.

    Makes sense because I believe mined limestone typically has negligible amounts of quartz sand, but if there is any impurity clay is pretty much the most common. Other pozzolans have much higher quartz contents. Although it’s not my area of interest, I am a geology graduate student who’s seen a lot of rock. I will add though that these tests were conducted with Portland cement, not S-Type Lime. There are also many different types of clays (and subsequently “baked” meta-clays), but kaolinite is common in some limestones. Overall though, I think the conclusions appear to be applicable to hydrated lime mixes considering the similar components of mined limestones, NHL, and S-Type lime with metakaolin.

    I also found a short article on crushed pumice (which is basically the same as volcanic ash for our purposes) used as a pozzolan sorta like what the Romans used. I’ll leave the link at the very bottom of this message. A comparison of this article to the research paper suggests that pumice may have some advantages, but may create a slightly weaker plaster. Even finely crushed non-crystalline pumice has significant potential to tear up lung tissue too (ask me about the paper if you’re interested). I know silicosis can still happen with a material like metakaolin, but the material isn’t a natural glass like pumice. I may be just biased, idk.

    I believe further innovation really needs to happen with alternatives to NHL. It is way too expensive and currently relies on shipping mountains of material across an ocean. While doing research on this, I was really surprised that there are not more established alternatives.

  38. Through general web searches, I found several companies offering pozzolan products (aka. metakaolin). I ordered a small amount of R-E-D Metakao 110-HR from RED Industrial Products in Grove City, PA and have been experimenting with it.

    As an introduction to to myself and my interest in lime…
    I have been researching hemp-lime for about a year as an eco build (wall fill) product. As you may know Hydraulic Lime will set under water, as well as speed the hardening. These characteristics have it’s benefits depending on it’s application. Do note that hydraulic lime is not necessary for hemp-lime (or other bio-fiber) mixes – but as can improve performance. Hydrated lime (from the building center) will work fine for mixes and plaster work. The exterior render can benefit from using hydraulic lime (natural or by additive).

    Now some comments from my initial testing of hydrated lime and hydrated lime with the added metakao. Both were mixed with water and placed in a small plastic cup to observe cure time. The lime with metakao (~25%) did have a quicker initial set time (although there was not much of a difference). After one week of setting up the two were very similar in hardness (finger nail test). The real value of adding metakao (RED) proved when I covered the two with water overnight. The mix with the metakao added showed no effect, other than being wet. The mix without the additive because to greatly soften and separate. This was done one week after the mixes had been made and placed in the cup to cure.

    I can provide contact and pricing info for RED Industries and pricing if anyone if interested.

    My next planned experiment will be to make some bio-fiber bricks. The plant fiber could be straw, hemp, wood chip or coconut coir.

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