Weep Screeds and Halloween

There actually is a connection between the most commonly used weep screeds and Halloween — they both can involve some scary outcomes!  The purpose of a weep screed in thin veneer wall is to provide drainage at the bottom of the thin veneer wall. Unfortunately, the manufacturer’s literature often states that this drainage space will come from the formation of a shrinkage crack. This is neither a predictable nor adequate solution for providing the necessary drainage of moisture at the bottom of a thin veneer wall.

A paradigm shift is needed when it comes to draining thin veneer walls. Most architects and builders now recognize the need for a drainage plane (commonly referred to in the industry as a drainage mat) behind thin veneers. These products create a space behind the veneer that acts as a capillary break and a transport mechanism to move water that gets into the building envelope down to the bottom of the wall. The problem arises when that moisture reaches the base of the wall; the most commonly employed weep screeds restrict the flow out of the wall because of that pesky shrinkage crack! And no, those tiny little holes are not for drainage. Again citing the manufacturer’s literature, they are for “attachment purposes (not weeping).

Moisture-related failure of walls is not as much about volume of water in walls as it is about the time that some moisture is allowed to remain in that wall. If an adequate opening isn’t available at the bottom of the wall for moisture to exit and adequate airflow to occur, the wall is ripe for failure.

I prefer to remain optimistic about the building industry, but I recently read an article in a national building trades publication on the correct installation of adhered masonry veneers that set my optimism back a bit. As many of you know, adhered concrete masonry veneers have experienced a large number of moisture-related issues when not installed properly. Many articles have been written about this issue including “Best Practices: Adhered Concrete Masonry Veneer” by Mark Parlee that appeared in the Journal of Light Construction. Parlee, who is a builder as well as a forensics expert, notes in his article that ACMV walls have now become a trigger for inspections because of the large number of moisture-related failures they have experienced. He goes on to state that the solution is “drainage.”

Back to the article I read. It implied that drainage was necessary, but it referenced the use of two layers of WRB to create that drainage. That is a very old technique, proven by testing to retard the rapid transport of moisture out of walls. It does not provide the minimum drainage space specified by respected scientists like Dr. Joseph Lstiburek. In his article Mind the Gap, Eh! a minimum 1/8” gap or void needs to be present to create a capillary break and an effective drainage mechanism.

The building trades magazine article also mentioned the use of a weep screed, but it did not indicate what to look for in an effective product. Remember, the holes are for attachment, and a shrinkage crack isn’t predictable. I am disappointed that while we seem to embrace the goal of better buildings, we still employ old, outdated techniques even though many of the new materials we build with don’t work with the old way of doing things.  We need that paradigm shift!

You need to look for a weep screed that provides frequent, large openings for drainage. They do exist. Without “real” drainage space behind the veneer and “real” openings at the bottom of walls, you will wind up with a moisture “trick” rather than the “treat” of a beautiful, long-lasting building. Happy Halloween, hope you get a treat!

*For more information about weep screeds and weeps at the bottom of walls, download the MTI article “MTI-014: Getting to the Bottom of Moisture Management” in the MTI Library at http://www.MTIdry.com.

ACMV wall failure in a Midwest hotel.

This photo shows a moisture-related ACMV wall failure in a Midwest hotel.


I know that imitation is supposed to be the sincerest form of flattery; however, when imitation is based on false claims, I’m not flattered!  MTI’s Sure CavityTM rainscreen drainage plane is the first and only rainscreen drainage plane on the market today that has “true” channels.  Sure CavityTM has always been configured with this channel technology since its innovative birth more than two decades ago.  Our competitors know that it is the “best” technology to quickly drain water from a high point to a low point and out of the rainscreen building envelope.  That’s why some are now claiming that they have “channel” technology, even though they don’t.

Webster’s New World Dictionary defines a channel as “a tubelike passage for liquids.”  Most school kids, if asked to draw a channel, would probably draw a couple of straight lines with some blue water in between.  When I did a Google image search for channel, the pictures that came up generally showed relatively straight banks (or sides) with water between those straight sides (ie. the Panama Canal, Erie Canal, etc.)  I am totally amazed how someone can look at a piece of fibrous plastic (think of a kitchen scrub pad) and see channels!  The whole idea behind an effective rainscreen drainage plane is moving moisture “quickly” down from a high point to a low point.  Water does not move quickly when it has to twist its way through a maze of fibrous material!  You can even add some vertical waves to the pattern but you aren’t really creating channels, and the fibrous makeup of the drainage material still puts a myriad of roadblocks in the path of the water you are trying to “quickly” get out of the wall.

A wise marketer once said, “It’s your ad, you can say what you want.”  I suppose that is true, but is it right?  MTI doesn’t have to make up product features in order to market our Sure Cavity rainscreen drainage plane products as the best moisture management solution.  We are the leader; our rainscreen drainage plane products have the technology others envy (and attempt to imitate), and our ICC and CCMC Evaluation Reports confirm that Sure Cavity works the way it is supposed to work.  No other manufacturer of drainage plane products on the market today have both a CCMC and ICC Evaluation Report for their drainage plane products.  None!  So I guess the old “Caveat Emptor – Let the buyer beware!” adage still hold true; kind of sad, isn’t it.