Masonry Magazine June 2010 Page. 19
Here's food for thought: Why does the masonry on a university library built less than 10 years ago require almost as much money invested in its repair as it cost to initially erect it? At the same time, consider how a building like Somerset House in London, built somewhere around 1755, has survived all these years without the benefit of a weep system or mortar collection device in its construction.
I'm not suggesting, by any means, that we change the way we construct today's brick veneer buildings. They are a far less expensive alternative to the old multi-wythe brick structures and, of course, much faster to build. Comparatively, brick veneer construction should also be much less prone to moisture damage, as it does not retain water the way a barrier wall structure may. As moisture migrates toward the inner wythes, it softens and weakens the mortar joints in the old construction, often leaving them to later crumble away. In brick veneer construction, while moisture still migrates inward, it is more easily managed, as we have the opportunity to collect, channel and redirect it - lessening the harmful effects indicative of moisture penetration.
The simplest details make all the difference. Here you see two problems with the installation: There is no sealant on top of the termination bar, allowing moisture to travel behind the flashing and the flashing does not carry the height of the mortar collection device.
What I am suggesting, perhaps, is that we continually may be rushing ahead of ourselves. The prospect of holding a proprietary specification gives birth to new products and the methods of using them, with little regard to their long-term function or compatibility with other materials and systems. So many new products and corresponding information are thrust upon the construction community month after month, it has become impossible to keep up with it all. Inventors or manufacturers bring new products to designers and specifiers who, in turn, require them to be used in projects before the contractor knows the intricacies of their installations. Unfortunately, as many good products as bad are lost in this process.
Nothing is more damaging to masonry than moisture. In fact, it is suggested that 90 percent of all masonry issues are moisture related. Over time, water will work to break down masonry joints and, if unprotected for long periods, it will degrade the anchoring systems within the wall as well. Prolonged exposure of moisture inside the wall will fuel a bloom of mold, efflorescence, or calcium encrustations, in some cases scarring the wall's face permanently.
In comparing old construction to new, the methods of moisture control differ significantly. Old construction uses ornate construction details like corbels and recesses to shed rainwater away from its façade. Newer, modern design incorporates less of these details and leaves the wall face much more susceptible to moisture penetration. The proper flashing materials, used correctly, are imperative to protecting the structures we build today.
Flashing's function
FIRST, LET'S LOOK AT what a flashing does. While flashing certainly offers a line of defense to the interior wall as a barrier to infiltrating moisture, we should not think this to be its only purpose. A flashing material in cavity wall construction needs to act as a means to moisture collection, and then more importantly to the diversion of it. Understanding that moisture inevitably will become part of the equation in a veneer wall is also the key to protecting the structure in the long term.
The quality of the flashings we use (a characteristic I find we ignore far too often) correlates directly and is crucial to the permanence of the wall. Synthetic membranes, peel-and-stick flashings, and all-in-one flashing systems that utilize synthetic membranes should never be confused with permanent moisture protection. Simply checking the manufacturer's warranty should give you a good idea of how long to expect the material to last.
Of all the materials I have had the opportunity to work with, a 5- or 7-ounce copper flashing still makes the most sense to use in all areas of the cavity wall. Its rigidity makes it self-supporting, yet they remain sufficiently flexible in the task of forming corners and end dams. Copper flashings exceed synthetics in puncture and tear resistance as well, assuring a stout collection area for any moisture pooling within the wall cavity.
As I said before, one of the most important steps to protecting a wall system from penetrating moisture is to acknowledge that it will likely be present. Let's consider some of the more common ways moisture permeates something as solid as bricks and mortar.
Wind-driven rain
ALL MASONRY MATERIALS are actually quite porous. This porosity can be accentuated further in different types of brick, or in varying surface cracks and imperfections in the masonry units. What's referred to as the "contact zone," or the area where the mortar and the bricks actually meet, is in fact the most porous part of the wall face and where moisture is most likely to enter unless repelled. Considering that mortar makes up 18 percent of the wall face, the area this contact zone makes up is significant to say the least.
The combination of water volume and wind pressure in a heavy rainstorm is probably the most significant factor of mois-