Masonry Magazine May 1978 Page. 16
PLANTERS
Planters must be carefully designed and constructed to withstand the effects of moisture and temperature. If a planter contains soil with insufficient drainage, plants will not flourish. Furthermore, if a planter contains excessive free water, the resultant expansion upon freezing can disrupt planter walls, resulting in structural failures. To prevent such disasters, provide weep holes through the bottoms or sides of planters, depending on the location and placement of the planter. Weep holes should be lined with preformed tubes of flashing materials and permanently soldered or joined to the planter lining to prevent seepage into the masonry.
WEEP HOLES
All flashing must be drained to the outside. Tests at the National Bureau of Standards indicate that concealed flashings in tooled mortar joints are not self-draining without weep holes. Rather they serve as a trap to collect moisture. Every 24 in., provide weep holes in head joints immediately above all flashing; keep weep holes free of mortar droppings. When wicks of 14-in. fiberglas rope or similar materials are used to prevent staining, weep holes should be spaced every 16 in.
CONSTRUCTION
Masonry must be relatively smooth and free of projections which might puncture flashing, destroying its effectiveness. For best results, place through-wall flashing on a thin bed of mortar and place another thin mortar bed on top to receive and bond the next course.
Flashing seams must be thoroughly bonded in a manner which prevents water penetration. Although most copper sheet metal flashings can be soldered, lockslip joints are required at intervals to permit thermal expansion and contraction. Many plastics can be permanently and effectively joined by heat or appropriate adhesive. The elastic pliability of plastic flashings eliminates the need for expansion and contraction seams.
EFFECT ON WALL STRENGTH
The effect of flashing on wall strength depends upon mortar placement and bond to both flashing and masonry. Although through-wall flashing does not affect a wall's compressive strength, it will reduce flexural and shearing strengths.
If flashing is placed directly on masonry with no mortar beneath it, the flexural strength is zero at that point. For this condition, the shearing resistance depends on friction. The coefficient of friction between copper flashing and masonry is probably in the order of 0.25 to 0.50.
Limited test data indicate that, where mortar is placed immediately above and below copper flashing, flexural strength is about 30 to 70 per cent less than for unflashed walls. There is not sufficient data to permit a similar generalization for shearing strength under similar conditions.
The important consideration is that through-wall flashing does not completely eliminate a wall's resistance to lateral forces. Fortunately, through-wall flashing generally occurs where flexural resistance is least significant. When the wall ends are restrained, the "arching action" phenomenon assists in resisting bending.