ACRYLIC COATINGS FOR COOL ROOFS

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Author Message Wayne Yancey Senior Member Username: wayne_yancey Post Number: 463 Registered: 01-2008 Posted on Friday, May 20, 2011 - 03:34 pm:    I have been warned (buyer beware) to stay clear of acrylic coating technology on SBS cap sheets because the acrylic coating is so thin it will prematurely crack and not perform over the long haul. Does anyone have factual evidence to backup this claim? White paper from an impartial independant source? Thanks, Wayne J. Peter Jordan (Unregistered Guest) Unregistered guest Posted on Friday, May 20, 2011 - 07:20 pm:    The field-coated acrylic-emulsion technology has been around for some time (more than 10 years). I am assuming you are talking about the factory-applied coatings offered by JM and GAF. Acrylic resins oxidize at a constant rate when exposed to UV radiation. One can calculate the "life" of the coating given the latitude of the projects to a pretty high degree of certainty. In our climate (Houston), this will be between 6 to 8 years (probably closer to 6). If we could get the Owner to recoat every 5 years with a good grade of acrylic house paint, the coating should last indifinitely. This coating should keep the roof membrane a little cooler, but there will still be movement over a year's heating/cooling cycle. Other manufacturers (like Derbygum and Soprema) offer a factory applied film membrane which also seems to be based on acrylic resins although they resist saying anything definite. Soprema does have some very good data to suggest that their reflectivity will continue within the EnergyStar guidelines. Again, I would suggest a regular recoating. I prefer the reflective granule approach from Firestone and Siplast. We will have to wait and see how long this approach keeps reflective, but it seems to be to be a more solid approach. I am more sensitive to the UV radiation issue because most of my professional life has been spent south of I-10 (with the exception of a misbegotten time in my 20s when I was in Atlanta--never want to live that far north again). The UV radiation is responsible for a lot of the oxidation that happens to materials and finishes. I want to scream when I hear that a product has been in service in Europe for 20 years; look at a map. Most of Europe is way far north of most of my projects (especially the ones in Diego Garcia, Guam, Fiji, and Palau). Two things to keep in mind: (1) The roof is going to accumulate dirt, more so in urban, industrialized areas. This will affect the reflective performance, probably degrading it faster than the UV oxidation. If you can get an Owner to simply wash the roof once or twice a year, it would maintain its tested performance longer. (2) The performance of these coatings should not affect the watertight integrity of the roofing although keeping the membrane a few degrees cooler may prolong the life of the roofing membrane. I have been looking into this stuff a lot for the last 15 to 18 months. This is my opinion, not really based on any hard research data, and I have certainly gotten some pushback from roofers and manufacturers; however, it seems to make sense to me. I welcome responsible opposing viewpoints. Jim Sliff Senior Member Username: jim_sliff Post Number: 57 Registered: 08-2010 Posted on Tuesday, May 24, 2011 - 12:04 am:    "Other manufacturers (like Derbygum and Soprema) offer a factory applied film membrane which also seems to be based on acrylic resins although they resist saying anything definite." I'd suggest requesting the MSDS for the actual coating. Most times it'll disclose what the marketeers don't want seen. I've not been involved with the shop-applied coating so I can't address it directly. But I'll do some digging on my own and see if I can gather any information comparing it to field-applied acrylics, which I DO have experience with. They're not usually my first choice (they usually end up used as a budgetary decision - thy certainly don't outperform other systems) but I have no problem specifying them. However, as Peter notes, inspections and necessary maintenance is a requirement at intervals based on the specific material, exposure and length of warranty (if any). The difficulty I have with shop-coated materials in critical exposures (roofing, immersion, high-abrasions etc) is that no matter how you write the specification rarely does anyone end up in the shop during application verifying the material and/or application are to spec. With large manufacturers it's usually not a problem - but it still ends up a low-budget system requiring higher more frequent inspections and inevitably higher maintenance costs. "the acrylic coating is so thin it will prematurely crack and not perform over the long haul." You're being given a meaningless "avoid" argument, however. Without specific test data and a definition of "thin" (as compared to what?) it's just repetition of non-acrylic producers' sales pitch. J. Peter Jordan (Unregistered Guest) Unregistered guest Posted on Tuesday, May 24, 2011 - 10:02 am:    I did try to look at the MSDS sheets and speak with appropriate technical personnel. I was unable to get the information for a meaningful analysis based on the manufacturer's viewing this as "proprietary" informationi/technology. One of them said they didn't give it out because other people might copy it. (I have received the same argument from other manufacturers.) The assume that their taking responsibility for the product relieves the architect of all liability. Evidently they are unaware of the legal responsibilities of the architectural profession. Paul Gerber Senior Member Username: paulgerber Post Number: 73 Registered: 04-2010 Posted on Friday, May 27, 2011 - 10:41 am:    I always shake my head when people want to use white roofs on projects SIGNIFICANTLY north of I-10...like Canada eh? I would agree that white roofs may make sense in the south, where cooling costs are high. But north of (or even close to) the 49th parallel we spend WAY MORE money on trying to keep the pipes (and people) from freezing in the winter than we do on trying to keep people from melting in the summer. IMHO, in my backyard darker roofs make a lot more sense than light or white roofs. Am I totally out to lunch on this one? Can anyone north of I-10 chime in with their thoughts? This is one of the instances where "chasing the credit" seems to trump common sense on a regional level. Ride it like you stole it!!! J. Peter Jordan (Unregistered Guest) Unregistered guest Posted on Friday, May 27, 2011 - 10:56 am:    The credit in LEED doesn't have anythng to do with a cooler building (well it does, but not in terms of temperature); it has to do with the "heat island effect." Dark roofs will tend to radiate heat held in the building mass to the night sky more effectively than light colored roofs. If I remember correctly, it is thought that the radiated heat is one of the causes of degredation to the ozone layer which contributes to global warming. The positive effect of the color on the membrane and the building below is, I believe, a side benefit. As with anything, there are trade-offs. The darker colors tend to result from carbon black which contributes to the plastizing properties desirable in a roof. So we do other stuff to get equivalent properties. Jim Sliff Senior Member Username: jim_sliff Post Number: 61 Registered: 08-2010 Posted on Friday, May 27, 2011 - 01:56 pm:    Paul's spot-on about reflectivity and how the whole "white roof" thing gets blown out of proportion. If I was designing (or owned) an open-beam ceiling building in Las Vegas a white reflective system or coating would make sense - but then again, why have a structure like that where you *know* heat's going to be an issue? IMHO insulation makes far more difference than the color of the roof in *most* cases. Peter, if they won't tell you what generic type of resin system is used, the recommended film thickness and application method (I want the manufacturer to specify application methods - NOT me!) and provide elongation, abrasion and flexibility data per applicable ASTM test methods I'd run the other way. Here's the reality-check - ALL coatings manufacturers buy raw materials from the same small group of manufacturers (the huge coatings companies make some of their own raw materials - and also make them for dozens of small and medium-sized manufacturers). And ALL of them, to some degree, use the resin-cooker's guide formulations as a basis for their own product's formula. There's nothing in the performance data and generic description that will tell anyone anything they don't already know. A shop-applied roof coating is still paint - it just *seems* different. When I see "proprietary (fill in the blank...resin, pigment, solvent, "additive" - MOST of the ingredients are "additives!) blend" on a MSDS my red flag goes up. That's an industry catch-phrase for one of two things - 1) we're using some good material blended with some cheap stuff and don't want you to know it, or 2)this stuff is so incredibly normal we can't tell you what's in it because marketing said so. I remember an old spoof on advertising for a "rubber ball" - might have been in Mad magazine in the 1960's: "Throw it up - it comes DOWN! Throw it down - it bounces UP! AMAZE your friends! Made from the same material as B-52 bomber tires!" I've found that if a manufacturer acts like they have something to hide, they usually do. MY personal catchphrase in these situations: "Next". Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 422 Registered: 10-2003 Posted on Friday, June 10, 2011 - 03:17 pm:    Speaking of practical - I've heard numerous indications that aircraft pilots don't like the white roofs in and around the landing patterns at airports. The highly reflective white surface creates extreme glare conditions. Ellis C. Whitby, PE, CSI, AIA, LEEDŽ AP Senior Member Username: ecwhitby Post Number: 108 Registered: 03-2003 Posted on Friday, June 10, 2011 - 04:16 pm:    Try metallic silver roofs. Some years back (at a different form) I was involved in an airport which featured numerous domes sheathed in stainless steel. The original design concept was for a #4 finish, but we had to have reflectivity tests to determine which facets had to have a rougher finish to avoid glare into the control tower. As I recall, the selected finish looked like someone was let loose with a ball-peen hammer.