In general, to obtain the best results, the superintendent should choose a fine, well-burned cement of average specific gravity, and, for important work, test it freynently. This, mixed with a sand that has passed a careful scrutiny for cleanliness and reguularitv, should give a smooth and strong mortar.
Protection. Whether lime or cement mortar is used in the building of a wall, it should be kept at all times protected from the weather until the mortar has become thoroughly set.
Brick Veneer. In some localities, dwellings and light mer cantile or public buildings are built with a frame of studs and board ing, veneered on the outside with four inches of brick. Tu this construction, the strength of the building lies in the frame, and the superintendent should see that this is built and braced in the best man ner, plumb and straight and boarded diagonally, all of well seasoned stock. Over the boarding, tarred felting should be placed, and an inch away from this, the four-inch brick wall, tied at short intervals to the wooden wall, as shown in Fig. 119. A metal tie such as at A may be used or the patented tie B, which is better.
As moisture will collect in the air space behind the veneer, the ties will be better if given a chip, as for hollow walls, and a small drain may be laid at the top of the foundation wall connected with the cellar by pipes for drip and yeritilation. This combination of masonry and woodwork is not to be recommended in general, but should only be used as a natter of economy.
The use of wood in the structure of brick walls, while some times necessary, should be avoided where possible. Wooden lintels were formerly used to considerable extent, but are objectionable for many reasons. Besides being combustible, it is almost impossible to obtain beams, of the large size which their purpose requires, which are dry, and the shrinkage is pretty sure to make a crack at some time. (Fig. 120.) Wooden plates inserted in the wall, for a level bearing for floor timbers, should be avoided, as their shrink age will leave the bricks above unsupported. Wooden lintels may be used under arches to form a square opening, but the arch should always spring from the solid wall beyond the lintel to relieve it from the load above. (Fig. 121.) Wooden strips are sometimes built into the walls for a nail ing for furring and finish, but, if used, should be thin enough to lay in the joint; and wooden bricks, often used for nailings, by their shrinkage will become loose besides weakening the walls.
A better way is to use a strong mortar into which the nails of the furring strips may be driven or porous terra cotta blocks may be set for nailings in special work.
Cleaning Down. When a piece of brickwork is completed, the exterior will need to be cleaned of mortar stains and discolorations. This is done 1w washing down the wall with a dilute solu tion of muriatie acid, using a scrubbing brush, followed by washing with clear water to remove all trace of the acid.
The wall is then often given a coat of linseed oil cut with turpentine. At this time also, all bad joints are pointed up, the spaces under window sills are filled up, the joints of stonework pointed, and the wall left whole and clean.
Waterproofing of Walls. Brick walls in exposed situations are often treated with some substance to render them waterproof. One of the most successful processes is known as "Sylvester's Pro eess," and consists in applying two washes to the walls, one com posed of Castile soap and water, and the other of adorn and water. '1'liese applied alternately will generally render the work impervious. Several patented are now upon the market, each of which is warranted to protect against moisture.
Efflorescence. Very disagreeable and very common is the white efflorescence which often appears upon the face of the bricks, due to the salts of soda and potash being dissolved by the water and left on the surface by evaporation. Sylvester's solution is a preventive of this, applied in the same manner as for waterproofing, and the danger may be diminished by using stronger cement in the face joints.
Repairs. In effecting repairs in masonry, when new work is to be connected with old, the mortar of the old work must be thoroughly cleaned off, along the surface where the junction is to be made, and the surface thor oughly wet. The bond and other arrangements will depend upon the circumstances of the case. The surfaces connected should be fitted as accurately as practicable, so that by using but little mortar, no disunion may take place from settling. As a rule, it is better that new work should butt against the old, either with a straight joint visible on the face, or let into a chase, sometimes called a "slip-joint " (I+ig. 12'2), so that the straight joint may not show, hut, if it is necessary to bond them together, the new work should be built in a quick-setting cement mortar, and each part of it allowed to set before being loaded. In pointing old masonry, all the decayed mortar must be completely raked out with a hooked iron point, and the surfaces well wetted before the fresh mortar is applied. Lining of old walls should be not less than eight inches thick, anchored every two feet.