Masonry Magazine June 2010 Page. 21
Conductance in a Building Envelope
A simpler definition would be a continuous path across a temperature difference, which we all know in extremes will cause condensation. In steel stud construction, consider the corner of a building with insufficient insulation. Cool, conditioned air from the inside of the building may be coming into contact with the much warmer air present in the wall cavity. In just a few months, you may have a significant problem on your hands.
Workmanship
I CONSIDER WORKMANSHIP to be the most significant factor of moisture penetration in masonry that we can maintain complete control over. Taking care to properly install materials by following the manufacturer's recommendations are pertinent details to good mason work. As noted earlier, attention to full mortar joints and correctly proportioned cement, sand and water in the mix also are major contributors to the longevity of the structure. The mortar joints also need to be tooled appropriately during construction, both to give the joints added strength and to provide the joints with a geometric shape conducive to shedding water. Good joint tooling reduces the permeability of the wall, period.
Now that we know some of the means by which moisture makes its way into the wall cavity, let's look at how we redirect it.
I mentioned the importance of flashing materials earlier. While there is no alternate for a quality flashing material, its presence in the wall system is not enough. Every flashing detail helps to maintain its continuity and, when overlooked, will undoubtedly lead to a failure in the collection system. These details, once again, speak to workmanship during the construction process.
The first consideration of the flashing system is continuity, or having the least amount of laps and seams. This also differs from material to material. Consider, if you will, an eight-foot section of 260-gallon, stainless-steel base flashing, While, without question, it should last well beyond the life expectancy of the wall, does it alone provide a continuous means to collect moisture? On a span of just 60 feet, you would require eight lap joints to complete the flashing end to end. Some of the newer "all-in-one" flashing systems on the market at five-foot intervals would require 12 joints! Everywhere a joint or seam exists, so too does the opportunity for a failure in the wall. In a copper or peel-and-stick flashing, you would require only one across this same span, if any at all.
The laps themselves are extremely important, and inevitable on just about any wall. Laps should be a minimum of six inches, and sealed with the manufacturer's recommended sealant or mastic. Mastics do, in fact, differ from one another, so compatibility is of tremendous concern, particularly when the mem-
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A 40-mil thick composite flashing consisting of a proprietary clear adhesive laminated to a polyethylene sheet. For use in both thru-wall and surface-mounted applications, Textroflash Green will not drool when exposed to UV or heat. It is UV resistant for up to 90 days.
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Resisted tearing and slicing
• Laps easily, just press at overlap