REPAIR OF MASONRY.
In effecting repairs in masonry, when new work is to be con nected with old, the mortar of the old 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," 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 com pletely raked out with a hooked iron point and the surfaces well wetted before the fresh mortar is applied.
The component parts of masonry structures may be divided into several classes according to the efforts they sustain, their forms and dimensions depending on these efforts.
1. Those which sustain only their own weight, and are not liable to any cross strain upon the blocks of which they are composed, as the walls of enclosures.
2. Those which, besides their own weight, sustain a vertical pressure arising from a weight borne by them, as the walls of edifices, columns, the piers of arches, bridges, etc.
3. Those which sustain lateral pressures and cross strains, arising from the action of earth, water, frames, arches, etc.
4. Those which sustain a vertical upward -or downward pres sure, and a cross strain, as lintels, etc.
5. Those which transfer the pressure they directly receive to lateral points of support, as arches.