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 thoroughly 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 " (Fig. 122), so that the straight joint may not show, but, 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.