The same situation usually applies to stone masonry. In some other cases, however, units are used which are sufficiently permeable to moisture that when exposed in a wall to heavy rain, leakage takes place through the units. With such highly permeable units, therefore, it is customary to apply stucco or other rendering to ensure resistance to rain penetration. Lack of Bond in Brick Masonry Unbonded areas between brick and mortar, which usually are the cause of leakage in brick walls, may result from faulty construction techniques in which insufficient mortar is used to form the joint, or from an unsuitable combination of brick and mortar. Well with the brick.
Some mortars resist loss of moisture better than others.
Such mortars may remain plastic long enough so that good bond is developed when the next brick is placed in the mortar. The interaction of brick and mortar when they are brought together in the construction of the brickwork therefore determines the completeness of the bond between them. If the bond is incomplete, rain penetration through the unbonded areas is a possibility. This reduces the suction and so produces a better condition for bonding with mortar. In this way, by the time the last brick has been placed, the mortar is still plastic and has good bonding properties, whereas a long mortar bed would have lost its plasticity and the last bricks set in it would be poorly bonded.