FLASHING... Tying the loose ends

Installation at Wall Base

Moisture which does penetrate the wall, gradually travels downward. This makes the base the most vulnerable location for moisture accumulation. A continuous flashing must be properly installed above grade. Various methods of installation for both veneer and cavity wall systems are shown in Figures 10 & 11. Proper weeping to provide moisture drainage is crucial. Weep holes MUST be used wherever flashing is located. They must be placed directly on the flashing, and spaced no further than 24" on center. Weep holes can be created in several ways. Some of the most common methods are: leaving head joints open, use of removable oiled rods, and installing plastic or metal vents (not tubes), in lieu of mortar in head joint. Cotton sash cords placed 16" O.C. will also serve as an excellent weep. There is no universal method. Different situations will require different methods. The specific type of weep hole is not critical as long as weep holes are properly installed at required locations in the proper spacing.

Keeping Cavity Walls Clean

A cavity wall is a drainage-type wall system. In a drainage wall, some water will penetrate the exterior wythe of masonry. The water then flows down the inside face of the masonry, is collected by properly installed flashing, and exits the wall through weep holes. Typically, the effective drainage space, or air space varies from system to system.

The space should be 1" for veneer work and cavity walls with closed cell insulation, and 2" for veneer on steel studs, or cavity walls without insulation. For proper drainage, it is important that this air space is free of mortar droppings, which can trap water within the wall system where it can cause damage. It requires a great amount of effort for the mason to keep mortar from dropping down into the cavity. Various techniques such as beveling the mortar bed away from the cavity and drawing a piece of wood up the cavity to collect mortar droppings can help keep the cavity clean. One recent innovation is the utilization of an insulated drainage board. (Figure 12) This system provides a narrower wall with an unobstructed drainage path, eliminating the need for a clean airspace.