This is a hunk of slaked lime from the bottom of an unstirred bucket, lime kept under water for three months undisturbed. Notice how firm it is. It's been laid on paper towels to absorb all external water off the hunk.
This is the hunk surrounded by unfired crushed limestone that has been sifted finely to make a fine white intonaco. This will be the Intonaco Pronto, which I'll pack up and carry with me.
Here is the 1:1 lime and small sand intonaco mortar, very stiff, very unlikely to crack because of shrinking lime. It doesn't have to be applied this thick. Lime shrinks because of too much water content. The rubber gloves are what I used to hand mush the lime and limestone. Don't get lime on your hands, if you do neutralize the lime with baking soda. If you get lime in your eyes wash them with milk and sugar.
I made a test on cracking by laying an 1/8 inch intonaco on glass and on dry wood. Four hours later both cracked a lot. Intonaco needs a wet base to draw from.
4000 B.C. Egyptians had watercolors and lime paint made from tin element based colors, and made plaster by heating limestone for murals and gypsum for building, adding alum to lime made a hard cement. Limestone powder is chalk or calcium carbonate. Gypsum is Hydrated calcium sulfate, a light spar. When heated to remove the water content both gypsum and limestone will make a plaster of Paris. The limestone crystal the is softer of the two and it contains no sulfur to effect the color pigments. Gypsum makes the harder more waterproof cement but has pigment color changing sulfur in it so it's not used for murals.
After slaking lime, remove all the slaked water off of the top. This is clear lime water. The longer you wait the harder the sediment lime compacts it's self, but it will never dry under water. Lime and water don't mix. Lime that has been heated or calcined and has had all the water removed from the compound is very porous. When the grain of lime reaches it's total absorption capability the cell is very close to the weight of water and only the weight of the lime crystal will cause it to precipitate. The lime is heavy compared to the water molecule and it will sink, but slowly. Quicker as time goes on because the lime is contracting as it sinks and compresses with other lime. The lime crystal will dry in the water up to the point of squeezing 33% of the water out, it takes time. Stirred slaked lime can be from a thick yogurt after 4 months to like 70 degree F. butter after 24 months. that's called a buttery consistency.
When using two month old lime, put the quantity to be used on paper to absorb all the excess water. It won't stick to the wet paper, lime prefers to stick to itself.
Two to four month old slaked lime will not hold any more water and has cast out some water becoming heaver and sinking faster. Slaked lime sinks quickly. Out of the water it could shrink more and faster. Dried lime re-crushed sinks fastest but looses it's bonding power and it's alkalinity. At this point it makes a good white pigment. The lime we buy has been slaked once, dried and recrushed. The first wetting makes quicklime and it very caustic.
This compares a bag of crushed limestone, which is available at pool builder supply stores, where it's called called crushed marble. Here is how I sifted out the medium and large grains. As you can see there is a lot of unfired limestone in powder size, perfect for intonico.
To slake lime, sift in as much lime to the water as it will hold. Add a third more water and stir it up. This photo of lime after 4 months of slaking. Soon I will stir it up with my hands in latex examination gloves and have a smooth buttery lime paste to make into mortar.
Soak the tile, it should hold all the water it can with out a shine. It will give, not take from the mortar.
To make a fast mortar frame place two of the same size tiles on each side with a 9/16ths inch spacer under the tile being coated in mortar. Or raise the outer tiles, or cut boards to the right height.
Here are 27, 12" tiles drying for the Haleakala Waldorf School Project.
This should be the last fresco test I have to do, 01-19-05.
What is the compared open time between white cement and lime mortar?
I made two 8.5 inch tiles. One with a white cement rough and one with a lime rough, both with 1:2 small sand. Two weeks later I put on the intonaco, 1:1.
I'll point out the changes after the tiles were washed. On the first line, the white cement stayed the same. On the lime tile, because it was painted while the lime was very wet, the lime moved and mixed with the pigment. The final effect was it dried lighter.
The answer to the question is.. One hour for white cement verses seven hours for lime. If the lime is well taken care of, i.e. keeping it moist with lime washes and pressure troweling the unpainted areas as time goes on. With correct moisture and re-pressing the lime I have gone 10 hours.
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