Coatings group disagrees with Baxter

The recent article "Roof coatings: for better or worse" by Dick Baxter, president of CRS Inc., Monroe, N.C., in the May issue, page 50, prompted my letter.

Although the Reflective Roof Coatings Institute (RRCI) is aware of Baxter's frequent contributions to Professional Roofing, it is clear he is not well-versed in some key aspects of roof coatings.

To his credit, Baxter makes a key point about the need for evaluating a roof's condition and proper surface preparation before coating application. As roof coating manufacturers, RRCI members insist on proper surface preparation and note a primer is not a substitute for cleaning. In his summary, Baxter notes the need to understand the quality aspects of roof coatings and performance benefits they create.

Now for points where Baxter falls short:

  • Unfortunately, Baxter does not reference ASTM D6083, "Standard Specification for Liquid Applied Acrylic Coating Used in Roofing." This specification first was introduced in 1997 and most recently was revised in 2005. It is the industry standard test methodology and specification for acrylic roof coatings.
  • In his article, Baxter describes some rudimentary lab tests of questionable value he employs to evaluate roof coatings. He uses an autoclave at 220 F to measure moisture absorption. I don't think even he has seen a reflective or cool roof that is this hot, pressurized and wet. Actually, moisture absorption of waterborne acrylic coatings improves as they repeatedly are exposed to moisture. ASTM D6083 contains a test and minimum requirements for water swelling and permeance.
  • Baxter discusses drying time of coatings and uses a lab test to evaluate this. However, in actual field application, conditions such as air temperature, coating color, film thickness, relative humidity, wind and solar radiance have a tremendous effect on drying.
  • Baxter tests adhesion of roof coatings to glass. ASTM D6083 has a suitable test and minimum values for adhesion to specific roof substrates. He goes on to describe a simple adhesion test. But the criteria he imposes cannot even be passed by EPDM field seam adhesion techniques because these also fail adhesively.
  • Baxter also is misinformed about adhesion to a variety of roofing materials, citing TPO, APP-modified bitumen and certain coated metals as substrates where there are no suitable coatings.
  • Concerning reflectivity and hiding of dark-colored roof surfaces, there are numerous products formulated with "high-hiding pigments" specifically designed to completely cover black asphalt and EPDM membranes and provide a durable, white, highly reflective surface.

On balance, Baxter makes a few worthwhile points, but on key technical aspects that move the subjective discussion to objectivity, he overlooks industry-accepted methods already in place.

William A. Kirn RRC
Kansas City, Mo.

Following is Baxter's response to the article:

My article was directed to contractors to call attention to some pitfalls surrounding the use of roof coatings. It describes methods any contractor can use to evaluate different coatings he intends to use on any given project.

I'm not personally an advocate of ASTM International. Most ASTM specifications are manufacturer-oriented, generally describe the lowest common acceptable properties, provide no qualitative information and are used more as a "cover your ass" method by marginal suppliers when their stuff doesn't work.

Whether Kirn questions my test methods, they provide quick indicators of the properties of various coatings for comparison. Most methods I use can be used by any roofing contractor to compare prospective coatings without involving a testing agency that only would test to an ASTM specification and generally provide no useful information.

Regarding drying time: It is absolute fact as raised by Kirn that ambient conditions will dictate the length of time a coating takes to "skin." But when all coatings to be compared are set side by side in a perfect environment and drying time, or skin time, is dramatically different from coating to coating, I'll pick the quick skin every time.

I assure Kirn that when a surface is properly prepared and a coating has good adhesion properties, the woven glass fabric will tear out before the coating releases from a properly prepared surface/substrate. Along the same vein, my experience also is that a properly prepared and formed taped seam in EPDM roof membranes will hold as the EPDM tears around the seam.

I never said there were no suitable coatings for TPO, APP-modified asphalt roof membranes or prefinished steel. I only said special primers and perhaps some special surface preparation may be required to get the coatings to bond.

As for reflectivity, all white surfaces—including white coated surfaces—become dirty over time and lose their reflective properties. I don't recall having said white coatings would not adequately cover dark surfaces though some lesser-quality coatings may require multiple applications to completely hide dark surfaces.

The simple fact is coating properties vary significantly—even products from the same supplier. Some are better suited for roof system applications than others, but I wouldn't rely on an ASTM specification to tell me which ones!


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