Masonry Magazine March 2012 Page. 30
MOISTURE MANAGEMENT
During construction, masons often accommodate small dimensional tolerances in the length of a wall by varying the size of head joints. Therefore, some weep systems that are prefabricated to a specific size cannot accommodate these changes in the size of head joints.
End dams
THESE ARE UPTURNS that are constructed at the terminations of the flashing. End dams should be constructed wherever flashings terminate within a wall to prevent water from simply flowing off the side of the flashing within the masonry wall rather than being directed to weeps where it can flow out of the wall. End dams are constructed by cutting and folding the flashing material. Joints are soldered or sealed (see Figure 2).
Joints and laps
LOCATIONS where adjacent sections of flashing are joined are critical. Often, water can flow through the flashing at openings at lap joints. Laps in sheet metal should be either soldered or properly sealed, depending on the material being used. Expansion joints in long sections of flashing are particularly susceptible to water infiltration and should be avoided whenever possible. They are usually only required at expansion or control joints in the wall and in some sheet metal flashing assemblies. If a large section of masonry is constructed on top of the flashing, the weight of the wall sitting directly on top of the flashing will resist differential movement between the metal and masonry. The usual distance between expansion joints can therefore be lengthened.
Materials
AS WITH ROOFING SYSTEMS, there are numerous materials that can be used to flash different components of a wall. Each has advantages and limitations, such as but not limited to - durability, workability (ability to be formed and or soldered in the field), and cost.
Sheet metal
FOR CENTURIES, sheet metal has been widely used to flash masonry walls. Lead sheets similar to roof drain flashings were formed in various shapes within the walls. Copper was also common. The author prefers metals such as copper (16 and 20 oz.), lead-coated copper (16 and 20 oz.), and stainless steel (28 and 26 ga.). These metals have unique abilities in that they can be formed and soldered in the field and will not corrode excessively under normal circumstances. These metals can be field-formed into various shapes such as inside and out-side corners, step flashings, or at unusual penetrations. Sheet metal is typically more durable than membranes and can withstand masonry being constructed directly on top of it. Environmental and potential worker safety concerns have recently limited the use of lead and lead-coated copper. Combinations of zinc and tin are being used to coat copper and other metals replacing lead. However, many of these formulated products have not yet stood the test of time, and sheet metal workers may not be familiar with how such products have to be prepared or how they behave during soldering. Galvanized steel can be a cost-effective alternative to copper and stainless steel. However, corrosion staining will occur at locations where the galvanized coating has been cut, such as at the ends of the metal, and where the material is breached, such as by fastener penetrations. There are also different types of galvanizing with different longevity rates. Aluminum will corrode if it is placed in contact with fresh cementitious materials such as mortar, grout, stucco, and/or concrete and it is usually not specified for this type of construction. However, under certain conditions, painted aluminum can be used. The paint will protect the metal until the mortar cures. Aluminum can still not be soldered in the field, so connections are made with rivets or screws and sealed with elastomeric sealant. Therefore, avoid aluminum in masonry construction wherever possible. Limitations of sheet metal include the cost of the material and labor costs required to form the flashing and to construct water-