276. After a driving rain or sleet storm, a wall even as thick as 12 inches may be soaked through by rain. It is therefore not desirable to plaster directly on the walls; if this is done, the wall should be either made waterproof, built hollow, or furred with 1" x 2" furring strips (though the last named does not prevent the moisture coming through the wall itself).

277. There are several ways of making brickwork impervious to moisture. It may be painted with lead-and-oil paint, coated with paraffin, or treated to some of the numerous patented processes.

All the paraffin preparations are applied hot, the wall being first heated by a portable heater. This makes the application expensive, owing to the time and labor involved.

In another process, known as Sylvester's, the wall is covered with two solutions, the first one made of castile soap and water, and the second of alum and water.

Boiled linseed oil is often used on brick walls, and two coats will usually keep out moisture two to three years. Linseed oil affects the color of the brick but little.

The objection to lead-and-oil paint is that it entirely changes the appearance of the brick and stonework. Indeed, architecturally speaking, pressed brick and stonework should not be painted unless it becomes absolutely necessary. If a new building is to be painted, the walls should be finishe3 at least three months before painting, and then three coats should be given. This will usually last four or five years. Thereafter, one coat at a time will be found sufficient.

278. A liquid compound known as Duresco is manufactured in England and Germany, and has been used with good results in this country. Duresco has been successfully used to coat walls on the inside before they were plastered, and it is asserted that the passage of moisture through the plaster is thus successfully prevented. It is said that it not only makes the brick weatherproof, but improves their appearance. When dry, it has a hard, uniform, impervious surface, free from gloss, and will not flake off or change color. This preparation is imported in kegs containing 56 pounds, one of which will cover about 1,000 square feet with two coats.

A preparation manufactured in Boston, and known as Cabot's Brick Preservative, is extensively used, especially in the New England and Eastern states. It is claimed by the manufacturer that this compound will completely waterproof brickwork and sandstone, preventing efflorescence, the disintegration of brickwork by frost, and the growth of fungus. The natural texture of the material is not changed by the application of the preservative, which leaves no gloss. It is made colorless for use on any kind of brick, to make them waterproof; and with color added, to match the brickwork.

The material is put on with a painter's brush, as linseed oil, or lead-and-oil paint is applied. The brickwork should first be washed down with diluted muriatic or nitric acid. A gallon will cover about 200 square feet of ordinary rough brick, and one coat is generally enough, unless the brick are very soft and porous.

279. Asphalt, put on hot, and from 1/2 to 3/4 of an inch thick, should be applied to the top of brick vaults to prevent the penetration of moisture. When the vault is covered with earth, it is well to lay the top course of brick in hot asphalt, in addition to coating it.