Finding the correct Hydrated Lime for limewashing brick fireplaces and walls can be very confusing and downright frustrating with so many products sharing “Hydrated Lime” name. Hydrated Lime for Gardening/Agriculture is not the same as Hydrated Lime Type S and neither are High Calcium Hydrated Lime, used for whitewashing bricks. Yes, they are all white powders, but they are completely different substances. Knowing the difference is vital for successfully whitewashing brick fireplaces and homes.
Finding High Calcium Hydrated Lime for whitewashing brick can be a frustrating endeavor, especially when the salespeople at the hardware store are untrained. I went through this recently at my local Ace. I bought high calcium hydrated lime there last year without trouble but when I went to pick up more, they had a completely different brand with labeling “For Agricultural Use” made by OldCastle Stone Pro
I tried to explain that ag lime was not the same as hydrated lime for masonry use but they kept on. It was the beginning of the COVID-19 epidemic so instead of risking infection further, I said “Fine, load it.” As soon as I got home, I mixed a sample with water and instantly knew it was not the same. For a great explanation of the different types of hydrated limes available, this is from the International Building Lime Symposium 2005 “Limewash: Compatible Coverings for Masonry and Stucco”
In many parts of the world, hydrated lime is made from limestone with a very high calcium content (95%+) and is known as high-calcium lime.
Uniquely in the United States, hydrated lime for building construction applications is made from dolomite (magnesium-containing limestone) and is slaked in pressure hydrators or by secondary steam processing that results in a lime of the very finest particle size. This lime is ready for immediate use and is so special that it is given an ASTM designation of Type S, Special Hydrated Lime. High-calcium hydrated lime in the U.S. may be designated as Type N, for Normal Hydrated Lime, and will require a soaking period of at least 24 hours in water prior to use.
Peter Mold & Richard Godbey
Dolomite Lime is not the same as High Calcium Hydrated Lime
Click on this link to see the differences in the types of Limes.
| Brand | Type | Chemical Makeup | Info |
| Greymont (also sold under Western Miracle brand name) | High-Calcium Hydrated Lime | Calcium hydroxide | SDS |
| Dolomitic Hydrated Lime Type S | Calcium magnesium hydroxide | Technical Info | |
| Chemstar (owned by Lhoist) | Type S | Technical Info | |
| Carmeuse | High Calcium Hydrated Lime | 85% Calcium hydroxide | SDS |
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