We all know the story of how Tom Sawyer tricked a bunch of boys into whitewashing his Aunt Polly's fence. However even though we've all heard of whitewash, most of us probably think it's paint. But in reality whitewash isn't paint at all, it's a very thin plaster, made by mixing water with lime and various other ingredients. About the only similarity whitewash has to paint is that it's used to color walls (or of course fences) and you apply it with a paintbrush. Whitewash works just as well today as in Tom Sawyer's day, (and it's the only way you can duplicate true historical finishes), but to get some, you'll have to make your own.
Start by making a creamy paste from 5 pounds of calcium hydroxide (also called hydrated lime) with about 2 gallons of water and let it sit over night. (This water and lime mixture will combine and form what is known as 'slaked lime' - which is the basis of house plaster).
At the same time, make a salt-water solution by mixing 5 pounds of salt with 2 gallons of water.
After setting up overnight, pour off any excess water from the lime and water mixture then add salt water to achieve a 'pancake batter' like consistency.
Mix the two solutions slowly and add the salt water to the slaked lime. You can always make the mixture thinner by adding more water, but you can't thicken it by adding more calcium hydroxide.
Test your mixture by applying it to a piece of paper that can be dried quickly. If it's too thick it will dry looking coarse and granular.
Color your whitewash (if you want), by adding pigments that aren't affected by lime. A light yellow color comes from adding yellow ochre, and iron oxides can produce reddish or brownish tones.
Allow your whitewash mixture to set up overnight before your begin 'painting'.
Whitewash is more commonly applied to external walls, but it can be used on inside surfaces as well. It works well on plaster or adobe type walls where it actually forms a thin plaster layer that bonds to the underlying surface.
Before beginning to white wash, clean the wall surface to remove any marks or grease. Whitewash won't cover these marks, and they will show through your finished surface.
Be sure to cover your floors well, the lime in the whitewash will stain them.
Wet the wall surface (to help the whitewash spread) and then apply the whitewash using a wide paintbrush.
Use the tips of the bristles and apply a thick coat of whitewash. Don't bend the brush (as you do when applying paint), use a more free flowing arm motion. (Whitewash is thick and it doesn't go on as easily or smoothly as normal paint).
Whitewash will often appear blotchy when you are applying it, but it will dry to a brilliant white color by the next day.
Calcium hydroxide is a soil additive that should be inexpensively available at farm supply stores. You can use regular table salt or any bulk pickling salt. Rinse your paintbrush right after you have finished applying whitewash. If you don't the lime will quickly ruin the brush. Whitewash is not paint. It will wash away over time if exposed to rain, and if you lean on a whitewashed wall you'll likely end up with some white on your clothes. Other products that have been put into whitewash over time include glue, Portland cement, soap, milk and flour.
Wear gloves, long sleeves and eye protection when mixing and using your whitewash. Since it contains lime, whitewash is a caustic mixture.