WATIRPROOF BRIM MASONRY. It is often necessary to prevent the percolation of water through brick walls. This may be accomplished in any of three ways, viz.: (1) by surrounding the wall with an impervious shield of tarred paper or bituminous felt, or (2) by making the masonry itself impermeable, or (3) by applying a waterproof coating to the face of the wall.
1. For a discussion of the first method, see § 384.
2. The second method requires the use of hard impermeable brick and the filling of all the joints with waterproof mortar. The mortar may be made waterproof by (1) securing a well-graded sand, (2) using enough cement to fill the voids, and (3) thoroughly mixing the ingredients (see § 369-77). Owing to the difficulty of getting all of the joints filled solidly full of mortar, more care and attention is required to make brick-work impervious than to make concrete waterproof (§ 363-84).
3. The waterproof coating may be a plaster of impervious mortar (§ 382), or a coat of bituminous mastic, or an impervious wash (§ 379-81) or paint. It is somewhat easier to make a plaster of cement mortar adhere to a brick wall than to a concrete surface (§ 382), but considerable care is required to secure success with the former. One of the most common methods of rendering brick-work water proof is to apply successive coats of alum and soap solutions. For the method of preparing and applying these solutions, see § 379. These washes have long been in successful use for making brick masonry impervious. The Transactions of the American Society of Civil Engineers, Vol. i. pages 203-08, contains an account of the stopping of leakage through a brick wall under a head of 36 feet by an application of "four coatings." Brick masonry, particularly in a moist climate or in damp places—as under a leaky gutter or in cellar walls—is frequently disfigured by the formation on the surface of a white deposit, which is called efflorescence. This deposit generally originates with the mortar, but frequently spreads over the entire face of the wall. The water which is absorbed by the mortar dis solves the salts of soda, potash, magnesia, etc., contained in the lime or cement, and on evaporating deposits these salts as a white efflores cence on the surface. With lime mortar the deposit is frequently very heavy, particularly on plastering; and, usually, it is heavier with natural than with portland cement. The efflorescence some times originates in the brick, particularly if the brick was burned with sulphurous coal, or was made from clay containing iron pyrites; and when the brick gets wet, the water dissolves the sulphates of lime and magnesia, and on evaporating leaves the crystals of these salts on the surface. Frequently the efflorescence on the brick is due to
the absorption by the brick of the impregnated water from the mortar.
This efflorescence is objectionable chiefly because of the unsightly appearance which it often produces, but also because the crystal lization of these salts within the pores of the mortar and of the brick or stone causes disintegration which is in many respects like frost.
As a palliative, Gillmore recommends* the addition of 100 lb. of quicklime and 8 to 12 lb. of any cheap animal fat to each barrel of cement. The lime is simply a vehicle for the fat, and should be thoroughly incorporated with the cement before slaking. The object of the fat is to saponify the alkaline salts. The method is not entirely satisfactory, since the deposit is only made less prominent and less effective, and not entirely removed or prevented.
As a preventative, make the wall as impervious as possible by using some of the methods mentioned in § 642. If the wall stands in damp ground, one or more of the horizontal joints should contain a layer of tarred paper or bituminous felt to prevent the wail's absorbing moisture from below. Particular care should be taken during the erection of the building to see that the roof, cornice, and gutters are made water-tight; and all ducts that carry water or steam pipes should be waterproofed on their inner surfaces. After the building is finished, if the efflorescence appears, first of all any leakage of water into the wall must be stopped; and if the efflorescence is due to the penetration of rain-water through the exterior face of the wall, then the face may be rendered impervious by the application of one or more pairs of the Sylvester washes (§ 379), which will not materi ally darken or discolor the bricks.
Efflorescence will gradually be blown away by the winds and be washed off by the rains,, but it can be entirely removed with scrubbing-brushes and hydrochloric acid mixed with at least four or five times its volume of water. Before applying the acid, the wall should be well dampened; and after being scrubbed, the wall should be thoroughly washed with clear water.