Whether it's a cavity wall or a single-wythe CMU wall, installing a system for draining that water is an essential part of building the wall. Moisture-control systems have been around as long as cavity walls. Recent improvements in materials are making those systems better in terms of operation and ease of construction. Even lower-cost buildings that once would not have gotten a moisture control system are now getting one. Several distinct parts make up a moisture-control system. These products are available from a number of sources, with variations in quality, cost, and features
A mortar droppings collector prevents excess mortar dropped into the cavity during construction from blocking the weeps and drainage paths. The most popular systems use a polymeric geotextile that sits in the bottom of the cavity and catches excess mortar dropped into the wall. Another way to maintain drainage in the cavity is to use a drainage mat placed against the inside face of the outer wythe. This system usually includes foam insulation boards with the drainage mat bonded to one side, although a very narrow cavity might have only the drainage mat. Another approach is to catch the mortar droppings above the bottom of the cavity to assure that weeps are not blocked.
Traditional high-quality flashings are made of copper or stainless steel. Copper and stainless steel flashing, properly installed, are guaranteed to last the lifetime of any building. These materials have nearly equivalent costs, but the initial cost is considerably higher than for the elastomerics. Metal flashings, however, must be prefabricated, and there is always the danger that construction tolerances won't match up with what's been supplied. Field changes can be difficult and require special skills. The many self-adhering flashings that have become so popular overcome that problem. The big negatives with the so-called peel-and-stick flashing materials are degradation in ultraviolet light, incompatibility with some sealants, and poor performance at high or low temperatures. Metal edges are always necessary, assuming the flashing is going to be brought to or through the face of the wall, where it should be. The steel keeps the self-adhering flashing material away from the UV and can be sealed to the masonry below.
PVC has the lowest cost of all commonly used flashing materials. Although, apparently some high-quality PVC flashings have had success, in general, PVC has not proven itself durable enough for masonry flashing.
Weeps can be, and often are, simply left open. It may not be aesthetically ideal, but it certainly works. Perhaps the greatest danger of open weeps is that some misguided maintenance worker will conclude that the open joint is a mistake and fill it with caulk. Another potential problem is that insects, wasps, or red assassin bugs may use the open weeps to set up housekeeping in the wall.
For small weep holes, the only real vent option is to use cotton wicking, either with or without a plastic weep tube. If you use wicking, be sure the wick extends back into the flashing several inches. Cotton wicking will eventually rot away, leaving an open weep hole.
Head joint weeps, placed immediately above the flashing, are also effective in allowing ventilation of the cavity as long as some sort of vents are also installed near the top of the wall. For these weeps, the options are T-shaped plastic vents, cell vents, small pieces of drainage mat, and polyester mesh.
Draining the water out of a single-wythe block wall is also important. Many of the above products can be used for this purpose. There are other specific products as well.
These products, still in their infancy, may or may not turn out to be successful in the long run. But they all point out that the masonry industry is thriving and looking for simpler, faster ways to achieve quality masonry walls.
The article list manufacturers of self-adhering flashing and other products mentioned.