ABSTRACT
This chapter deals with the many problems affecting walls. It addresses the issues of stability and weathertightness, both of which are common walling problems.
Rising dampness in walls is likely to cause damage to internal plaster and decorations, particularly when hygroscopic ground salts are brought up in solution, as they generally are. The line of dampness due to the complete absence of a DPC is usually fairly continuous and roughly horizontal, and can extend several feet in bad cases. Remedial measures much depend upon the nature of the wall. If they are
of brickwork or coursed stonework, in some instances, it may be feasible to cut a slot in the wall and insert a DPC or to inject a chemical damp-proofing system. Old walls of random masonry construction are unlikely to yield to these treatments and these can be nearly impossible to damp-proof. But see Douglas (2006) for measures to minimise the need for a retrofit DPC. However, this book is concerned principally with the avoidance of fail-
ure in new construction and one would not expect the complete absence of a DPC in such work. A more common problem in modern construction is bridging of the cavity wall by excessive mortar droppings at the bottom of the wall (Figure 10.1). This leads to irregular damp patches appearing adjacent to the mortar droppings. If such poor workmanship cannot be prevented then, fortunately, the remedy is not too expensive (see Figure 10.2). Bricks will need to be cut away and the cavity cleaned out. Inadequate laps in flexible DPCs can also lead to moisture penetration. Laps should be of at least 100mm and the DPC laid on a full mortar bed and also fully covered with mortar above to prevent damage. It is not uncommon for the DPC in the external wall to have been bridged by pointing,
or rendering, over it. This should be prevented by projecting the DPC slightly through the external face and by stopping any rendering short of it. Bridging can also occur through over-zealous gardening, a common cause being the heaping of soil against the wall or the construction of patio paving above DPC level. Such gardening activities, if afterwards remedied, will give the home owner two lots of backache and a stained wall.
