The chief objection to whitewash is its lack of durability for outside use, requiring frequent renewal. Besides this, it is apt to powder off on one's clothes. The following method will serve for preparing a whitewash for inside use that is reasonably free from this defect: Take good builder's lime, and slake it by soaking it with warm water, allowing it to fall into a fine powder in the open air. Make it very thin by the addition of water, and to every pailful add a pint of flour previously made into paste, or, bet ter still, add a solution of one pound of ordinary alum in hot water to every gallon of whitewash. The first coat should be applied very thin, so as to bind to the wall. The addition of alum will prevent the second coat from rubbing up the first coat, and will thereby make a more uniform surface.
To make whitewash that will stand the weather reasonably well, add one part of salt by weight to three parts of lime.
Another method of preparing a whitewash for outdoor work, so that it will stand the weather reasonably well, is to take one pound of lime, and slake it with warm water. Then take one-quarter of a pound of Burgundy pitch, and dissolve it by gentle heat in a pint of linseed oil. Add to the hot lime one gallon of skimmed milk, and then polo in the mixture of pitch and oil, a little at a time, stirring constantly. Finally add three pounds of bolted whiting. If too stout to work evenly, add more skimmed milk. This, however, ceases to be a true whitewash, and par takes more of the nature of a paint, since it de pends for its binding properties upon the milk, the linseed oil, and the pitch.
The United States Government has a formula for a cheap and fairly durable water paint for exterior work—on lighthouses, etc. To prepare it, one-half bushel of lime is slaked with boiling water, and kept covered during the slaking to retain the steam. When cold, it is strained through an ordinary sieve or paint strainer; and then one peck of salt dissolved in warm water, three pounds of rice flour stirred in water and boiled to a thin paste, one pound Spanish whit ing, and one pound pale glue dissolved in water, are added to the strained lime mixture, thor oughly stirred, and allowed to stand well covered for several days before using. This wash must
be warmed in a kettle before using, and applied with wall brushes as hot as possible without in juring the bristles. Such a paint wears well on wood, brick, or stone. If a buff tint is desired, French ocher, ground dry, may be used as a col oring; and if a reddish tone is desired, Venetian red should be used. A reddish buff is obtained by a combination of ocher and Venetian red. Chrome yellow should not be used, as this pig ment is affected by lime.
A red wash can be made by mixing dry Vene tian red, to which whiting or quicklime is added, with skimmed milk. The addition of a half gallon of linseed oil to each gallon of this wash will render it waterproof; but even without the oil it will stand for years.
It will noted that some of the washes men tioned above depend partially for their binding properties upon casein—a product of skimmed milk. Casein paints are usually sold in pow dered form, the casein being dried and added to the lime, whiting, or powdered cement that is used as the pigment base. The coloring matter is also added to the dry powder, and the whole thoroughly mixed by machinery, so that the addition of water is all that is required to pro duce a paint which is used in the same manner as oil paint and which covers fairly well. Such paints dry with practically no gloss. These casein paints are generally known as water paints, and are manufactured by a number of firms, all of whom, however, are required to pay a royalty to the owners of the basic patent. They are useful for all sorts of outbuildings, for painting brick walls, and especially for the in terior of factories, warehouses and sheds. While they cannot be said to be weatherproof, in the sense that linseed oil paints are, still, they will stand considerable exposure to the weather, and on old weather-beaten woodwork may be used as a priming under an oil paint, provided the very best results are not looked for.
Still another class of water paints are put up in paste form—depending upon silicate of soda or water glass as the binding agent. These paints have given good satisfaction wherever used, especially on brickwork, but are more expensive than the casein paints.