Basically we sifted lime into water -- and then had to wait at least 6 weeks before using that lime to make fresco. This process is called "slaking" the lime. Some say that you need to wait at least 2 years before using the lime, and add that the longer you slake, the better (although my five year batch dried up when I wanted to use it).
We wanted to use clean lime and clean water, to reduce the chances of the final fresco cracking. Therefore we bought a five gallon jug of water at the Circle K, and lime for making tortillas in Mexico. The Home Depot lime might have impurities that would make a fresco crack; likewise, the minerals in tap water might make the fresco crack.
5 gallons of pure water from Circle K:
Tortilla lime from Mexico:
Let the Slaking begin:
Added water first, into a heavy duty garbage bag (inside another heavy duty garbage bag -- double bagged):
Josh sifting lime into water, with a cake sifter. The object is to surround all the lime dust particles with water. Note, the lime sits on the surface of the water for a bit, and then coagulates, before sinking into the water. Therefore you can't really sift too fast.
Lime into water. Waiting for what is sitting on the surface to sink. Lime dust collecting on the sides of the garbage bag:
We sifted enough lime to almost fill the bucket, but not surfacing above the standing water. I left a little more water on the top, because I did not want the fresco mix to dry out during the hot Tucson summer.
Made almost 4 buckets of slaking fresco lime from 50 pound sack of tortilla lime. Labeled the buckets "March 5th, 2009." Now we had to wait for at least 2 months, Cinco de Mayo, before using the lime to paint fresco:
Sifting the lime raised a lot of dust, which is not good for your lungs. I should have used a better mask, such as this one:
I was suspicious of the industrial lime at Home Depot, but perhaps it would have worked just as well. I will never know unless I try it:
here is a link to the video demonstrating prep of "practice lime" from home depot stuff.
ReplyDeletehttp://www.youtube.com/user/FrescoSchool#play/user/98DABB7AA50F8B37
it is not good for painting - "S" stands for special - high magnesium content good for commercial stucco.
bagged powdered lime should always be the second choice, because calcium hydroxide in it has already partually turned to calcium carbonate once exposed to air during bagging/storing/etc.