An excellent way to improve the resistance of any brick wall to water penetration is to plaster mortar on the back facing, or to plaster the face of the back-up wall units, depending upon which is laid first. The mortar used in plastering is the same as that used in laying wall units. Usual thickness for plastering is from 1/4" to 1/2".
Before plastering is begun, mortar joints must be struck smooth. The use of plastering is recommended practice, and its effectiveness has been proved by field experience. It is generally necessary to adjust alignment of blocks after placing. Tapping a block into alignment after the mortar has stiffened is a serious infraction of the rules of good workmanship.
If the mortar bond is thus broken, water can penetrate the wall at this point. For good block work, Mortar Cement
provides sufficient body to the mortar to hold the weight of the block, and at the same time, the mortar retains sufficient plasticity to allow the block to be tapped easily into alignment. Unless otherwise specified, all exterior joints on concrete
block masonry should be tooled. A rounded tool
slightly larger than the joint is preferred.
Tooling of joints should not be considered a remedy for incomplete filling of joints. On block walls, architectural design may favor tooling only the horizontal joints, with the vertical joints being troweled flush. This is especially popular where the wall is to be finished with cement paint. An exterior coating of mortar is frequently plastered below the ground level
of concrete block basement walls to make them more waterproof. Walls are plastered on the earth side from top of footing to 6" above the ground level with two coats applied according to procedure under STUCCO
. When second coat is properly cured, it should be brushed with an asphalt primer and two coats of hot bituminous material.