The ascent of damp is guarded against by the use of damp-proof courses, of different materials, laid across the whole width of the walls, a little above the general surface of the ground, and under all timbers, wall plates, etc., which are liable to be affected by damp. The following kinds of damp-courses are employed in different parts of the country: -
1. Blue brick damp-courses; which consist of blue bricks, with open cross vertical joints, laid in cement, and with the two next courses of brick, above them, built in cement mortar. This is a most effectual method, besides being inexpensive, and raising the building at the same time - assuming that there can be no objection on the score of appearance.
3. Asphalte damp-courses of Val-de-travers, Seysell, or Limmer asphalte, are very effectual, though a slightly more expensive remedy; still they have the advantage of being hidden in the joint, whereas the blue bricks would be apparent and out of character. The asphalte should be laid on hot, and by experienced workmen.
4. Anderson's, McNeill's, and Engert & Rolfe's patent fibrous asphalte felts are another effectual remedy, and particularly convenient; because, as sold, they are ready to be laid by the ordinary workmen, being made in lengths and to the widths of ordinary walls. They are either laid in single courses, lapped at the joints, or double - i.e., in two thicknesses.
5. Cement and sand, gauged strongly (as one of cement and one of sand) is sometimes used as a damp-course; and it is effectual, but requires time to set, before any heavy work can be built on it.
6. A composition of tar, sand, and pitch is a common and successful remedy; though it requires experience in the boiling, as it will only set properly when laid on hot immediately after it has reached a certain state after boiling.
7'. Lead is sometimes - though seldom nowadays - used as a damp-course. It is expensive, because it must be stout; besides which it has the disadvantage of being affected and eaten away by cement or lime; and it will not carry very heavy weights.
8. Hollow vitrified brick blocks, to allow the circulation of such a non-conductor as air, are also another effectual remedy, and frequently used. They are laid on in two courses, breaking joint.
9. Calender's bituminous damp-proof sheeting is very effectual, as well as reasonable in price, and it can be applied in continuous lengths.
The descent of damp, in special cases, such as parapet walls and chimneys, is stopped by similar methods to its ascent, as explained above. The common method, however - which only checks, but does not prevent the descent of damp, in ordinary walls and other places where it penetrates or descends - is to throw it off by weatherings and projections. All string-courses\ sills, copings, and projections should be weathered or splayed, and the underside "check-throated," so that the wet runs down, and being checked by the throat on the projection (as at x in fig. 193), drops off.
Copings of stone or blue or red bricks are also used at the top of walls for this purpose, and may be either weathered and throated, as fig. 193;saddle-back and throated, as fig. 194; rounded and throated, fig. 195; or bull-nosed or half-rounded, fig. 196. All these are effectual except the last; this does more harm than good, as, without the throat, all the wet is collected and literally poured down the face of the wall.
A tile creasing, as shown in fig. 197, is often also employed as a coping and projection to walls, and consists of two courses of tiles breaking joint, and built in cement, projecting from the wall line.