Estimating Your Natural Hydraulic Lime Order –

Written by Andrew Morrison

Plastering is hard enough, so don’t beat yourself up trying to figure out how much plaster you will need. The first option I HIGHLY recommend is to contact the management at the place from which you intend to order your material and ask them to calculate the order. You can give them your building’s dimensions and other details they request and they will give you a very accurate bag count and sand quantity for estimating your Natural Hydraulic Lime Order. In fact, they will most likely be more accurate than you will with the formulas below.

There are two major players in the Natural Hydraulic Lime Plaster arena. The East Coast is covered by De Gruchy’s Lime Works located in Pennsylvania. They will happily help you estimate the material order and are also able to send out samples of materials and colors to help you choose the final coat material and color. They ship directly to you and if you use my vendor code (95501NHL) they will give you a discount on any purchase you make. Check out their website at You can also purchase a cool plaster application gun that allows you to spray on your plaster, speeding the application process!

Saint Astier Plaster

The West Coast is Handled by one main distributor: TransMineral USA, Inc. located in California. They supply many retail stores with the plaster and can also drop ship larger orders directly to you. The folks there are always happy to help clients get the order right, the first time. You can check out their website at Let them know that I sent you and they may be willing to help you out a bit on the product pricing. I can’t make any promises right now, but it is possible.

Person standing in front of chalk board

So if you insist on doing your own calculations, give the following numbers a shot. Best of luck and don’t forget to plan for the necessary excess of mistakes and dropped mud. The following is based on an estimated wall surface of 900 Square Feet. I have also used the NHL 3.5 as the material as that is the norm for my climate. DO NOT assume that this is the right material, and therefore ratio, for you. Ask the folks above to help make that determination. Also, I have given you a couple different options for the sand/lime mixing ratio. The more lime, the stickier the plaster. The more sand, the less expensive the plaster.


Alternative 1:

Scratch Coat: 1 part NHL 3.5 to 1.5 parts sand (mixing ratio) at 3/4″ = 1440 lbs.
Brown Coat: 1 part NHL 3.5 to 2 parts sand (mixing ratio) at 1/2″ = 728 lbs

Total Scratch & Brown = 2,168 lbs / 55 lb bags = 40 bags

Alternative 2:

Scratch Coat: 1 part NHL 3.5 to 2 parts sand (mixing ratio) at 3/4″ = 1092 lbs.
Brown Coat: 1 part NHL 3.5 to 2.5 parts sand (mixing ratio) at 1/2″ = 560 lbs.

Total Scratch & Brown = 1,652 lbs / 55 lb bags = 31 bags


Alternative 1: 1 part NHL 2 to 2 parts sand (mixing ratio) at 1/8″ = 164 lbs or 3 bags

Alternative 2: Ecomortar F premix at 1/8″ = 14 bags (This is much easier to use than mixing with sand. I strongly recommend the pre mix bags.)

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22 Responses

  1. Hi Andrew, I cannot find NHL in S.A. The only product is hydrated lime wich is the same but there is no grading like a 2.3 or 5. Is it ok to mix hydrated lime the same ratio as your NHL. Barnie.

  2. Hi Barnie. I am not familiar with Hydrated Lime ratios. I suggest you contact someone locally who understands the materials. The fact that it is to be applied on straw will not affect the mixing ratios.

  3. Barnie, be careful as hydrated lime is not the same as hydraulic lime. Hydrated lime cures only via recarbonation, so it cannot be applied very thick, thus it would work well for a finish coat, but not as a scratch or brown coat. See for an explanation.

  4. Hi Gene, Thanks a mil. At least somebody saw my letter. At this stage i am in a dead end and does not know wich way to go. I CANNOT FIND natural hydraulic lime in South Africa. I dont want to use a alternative for nhl unless there is no other solution. I would be very please if ANYONE with indepth knowledge about lime, cement and morters can help me to put a mix together that will have the same features as nhl. I need to mention that there is quite a number of strawbale projects ongoing in S.A. and if I can get a solution to our lime problem it will make a very big difference in the future development of strawbale building in S.A. We do have a variety of limes but not nhl.
    Greetings Barnie

  5. Hi Barnie. You cannot make your own NHL from other lime products, The cool attributes of NHL come from the way the product is manufactured. Check out the following website for information on the production process: I am sure that you can find someone to drop ship the product directly to you. I do not know if this will be cost effective though. Try contacting the folks at Transmineral USA ( see if they can help you. They import the product from France to the West coast of the US.

  6. You can make your own hydraulic lime or you can find it already made. It is called artificial hydraulic lime (AHL) and is frowned upon in placed like France and England where restoration work requires high quality control. One place to find AHL is at sugar beet plants. They use hydrated lime which is converted to a basic form of hydraulic lime during the sugar extraction process. You can also make AHL by adding some sort of pozzolan to hydrated lime, such as fly ash. It is highly recommended you experiment with these materials before applying them to your building.

  7. Gene,
    I don’t know of any sites that talk about it. This is based on my experience with NHL and hydrated lime, mixing the two, mixing hydrated lime with cement and just knowing those who have talked about it. I have not done it but want to try it out. Just haven’t had the opportunity. Other pozzolans include ground up pumice, rice hull ash, etc. Do some research on pozzolans. Much of it depends on what you have available locally.

  8. Hi Andrew, Jeff,Gene and Charles,I think Jeff came up with something for a lot of folks who have the same problem. Unfortunatly I am still out luck so far but at least there is something to work on. Any coments from your side Andrew.

  9. Hi Jeff, Do you perhaps have a ratio of the mix for AHL-Pozzolan and Hydrated lime etc? I am out of luck so far.

  10. Barnie,
    I am not as much of an expert in the science and art of plaster as some on this list. I cannot add anything more to the conversation at this point. I imagine there are those out there who have a much richer bank of knowledge when it comes to plaster. Seems like some are already engaged and I hope others will chime in as well.

  11. Barnie, et al,
    I am using hydrated lime and sand to make my plaster, as I learned from a member of the natural building guild in New Glarus, Wisconsin. Hydrated lime is a little more work in mixing but I’ve found it to perform well. I have made exterior stucco repairs and interior plasters (rough, scratch and finish coats) with hydrated lime.

    Ratios: 1 lime : 3 sand for scratch and brown coats, 1:1 or 1:1.5 for finish coat.
    Mixing: water first, then sand, then lime. Start with 1-2 liters water in a 5 gallon bucket, you can add more water after mixing a while if needed.

    You will notice it gets drier after the first 5-10 minutes, that’s the time to get you moisture right for troweling purposes. Try troweling a small patch or a sample board to get the water content where you want it.

    Mist with water at least twice a day after applying a coat of plaster. If outside, shade it from the sun. Wait 2-3 days between coats for carbonation, or longer if applying thick coats of one half inch or more.

    Lime wash finish: I am making lime wash with the same hydrated lime. The first coat can be thicker, 1 lime : 1 water : .1 salt (that’s one tenth of a part salt).
    Subsequent coats: 1 lime : 2 water : .1 salt
    Mix well and leave for a day before using.
    Wet the wall well the night before you will limewash. Do this for each coat.
    Apply in the shade, mist it with water after 30-60 minutes, especially the thick limewash. Wait 1-3 days between coats, and at least 3 days after plastering before applying the first coat of limewash.

  12. I’m interested in applying a tinted hydraulic lime skim coat to my interior walls.

    The existing walls are standard drywall with a hawk & trowel finish done with drywall mud.They have also been painted with primer & latex paint.

    I’ve been told that I can apply the hydraulic lime skim coat over paint but need to apply a product called Plaster Weld or M-Bond on the painted walls first.

    Any recommendations on how to skim coat painted drywall?

    How many coats of plaster?Do I need a traditional scratch coat? or just a base coat?

    What kind of mix ratio of sand to lime?

    Since this will be a thin skim coat I would assume NHL 2 with a fine silica sand would work?

  13. Hello there!

    Just wanted to let you know that there is another player in the natural hydraulic lime business in North America! We’re also introducing our natural hydraulic lime and natural expanded cork aggregates thermal render. If you wish to know more about it, please visit our distributor’s site in the UK: – they’ve been using our products and are very pleased with it. It’s great for use on strwbale or cob houses.
    If you wish to receive any additional information, please let me know! Thank you for your time

  14. HI Barnie

    I’d love to hear what you eventually settled on. We are also in South Africa and about to build a straw bale house.


  15. Hey both Rozanne and Barnie … Did you find a solution in SA?? I see that the Chloorkop mine in Kempton mines the Hydrated Lime (I’m glad I stumbled across this feed as I just assumed it was ‘basically the same thing’) – we’re about to begin our Bale house in Limpopo … And as thorough as Jerry McIntire’s mix is, it’s Africa; there is always sun.

  16. hi…building with mud in the Gambia. would really like to buy hydraulic lime….has anyone any ideas where I can purchase it? best wishes

  17. I don’t know in that part of the world. St. Astier Lime comes from France and they may have the ability to provide for you in Gambia as well. if not, you can make lime have hydraulic properties by adding brick dust or other materials to lime putty. Perhaps that is more available near you…?

  18. From an ecological point of view, importing NHL is absolutely nuts. It makes so much more sense to try and find natural pozzolans in the US instead of importing NHL from Europe.

    Even importing a pozzolan instead of NHL would have significant positive ecological effects. That would cut the transport footprint by more than half.

    In the Netherlands, Belgium and the western and southern parts of Germany, trass flour was a very popular natural pozzolan. Its popularity is growing again thanks to monument care and eco construction. The main deposits are around Andernach (near the Rhine river, Germany). .

  19. Totally fair statement. There is no question that local materials are best when the quality is the same. It’s possible to get a high quality lime plaster with hydraulic properties by using pozzolans; however, for someone with less experience, buying the highest quality plaster they can find may be the best, if not only, option to get a quality finish on their home.

    I don’t disagree with you at all about the importance of understanding the lifecycle of the products you put in your home; including transportation impacts. Thanks for raising that point Mark.

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