The letter-writers continue:
While the article discusses potential problems with detailing, it is important to consider a thick-mil manufacturer’s presentation to the Building Enclosure Technology and Environment Council (BETEC) of the National Institute of Building Sciences (NIBS) emphasized the importance of field inspection to avoid sagging of thick-mil materials.
In their article, the authors write:
It is an established fact the thinner a membrane is, the more difficult it is to achieve a complete and uninterrupted film during application. This is based on the marked variations in substrate porosity of exterior gypsum sheathing, concrete, concrete masonry units, etc.
It is important to note this refers to thick-bodied products that lay on top of the surface. They must be applied at a thick millage to ensure membrane integrity. Thin-mil products absorb and fit themselves into the substrate, thus assuring a continuous membrane. That is why thin- mil products have been successfully tested on CMU to demonstrate air barrier performance.
Under the section, “Testing specifics,” the authors write:
Thin-film FAAB performance standards are tested at X mils. However, the specifications may require Y thickness, which is often two to three times that ‘X.’ This leads to the question of what those performance characteristics are at Y thickness.
We occasionally see specs we believe to be oversights, which call for thin-mil products to be applied at thick-mil thicknesses despite the literature of the thin-mil product calling for a thin-mil application. In those instances, we suggest the spec be revised.
The article included a photo showing a sheathing manufacturer’s logo visible through the coating. It is important to note when this occurs, it may simply be a complex interaction of:
- coating design (including not loading up a coating that will remain unseen during the life of the building with components to enhance hide that will only drive up costs);
- substrate absorbency (which may not impact coating performance); and
- stability of the logo pigment.
In such cases, the coating manufacturer can help sort out these issues and ensure a performing application takes place.
The authors also mention racking forces. It is important to note many thin-mil products meet demanding racking tests imposed by ICC-ES—tests many thick-mil manufacturers have not performed.
Under “Durability and exposure,” the authors write:
Some building envelope consultants have been concerned with the influx of newcomers in the FAAB market, requiring them to comply with various ASTM test procedures. In some cases, they have tested fluid-applied air barriers to ASTM D471, Standard Test Method for Rubber Property Effect of Liquids. This test is intended for rubber ([EPDM]) pond liners, not FAAB.
While our company does not test under ASTM D471, we note the authors emphasize the importance of ASTM C836, which, as mentioned, relates to “cold-liquid-applied elastomeric waterproofing membrane for use with separate wearing course,” and was not intended for FAABs.
Finally, the article closes with some discussion of ASTM Committee E06−Performance of Buildings’s Work Group WK50742, which is writing a new standard, Standard Practice for Assessing the Durability of Fluid-applied Air and Water-resistive Barriers. In our opinion, it is important the ASTM process not be used to perpetuate products with physical properties—such as high elongation—that happen to be features of long-marketed and long-specified products, but do not impact real-world performance. Further, the ASTM process must not impede the introduction and market viability of sound product innovations. As the authors say, “Of course, in any area of building science, newer technologies are not to be ignored, and should be heralded.”
As thin-mil products (especially those marketed with fluid-applied flashing that replaces peel-and-stick and provide project-specific detailing) gain market share, we expect to see continued use of ‘durability’ (there is no abrasion in this application), ‘crack-bridging’ (despite structural defects and thick-mil products requiring pre-treatment of cracks), and ‘high elongation’ (patterns with structural failure) asserted against them. As an old salesman once said, “You have to sell what’s on the truck.” Perhaps some product innovation would be a better course.
We shared the letter with the original article’s authors, who have replied with the following:
Thanks for passing along these comments. Some of the discussion in the letter—such as the relevance of ICC code-compliance of FAABs—deals with topics never referenced in our article. However, I do take particular issue with the explanation that being able to see sheathing logos flashing through thin films is a result of “the logo’s pigment stability,” along with the statements that “substrate absorbency doesn’t matter” and “building up the FAAB” does nothing more than “increase costs.” These points simply do not reflect what we are seeing in the field.
