Hi, everyone! I hesitate to put this post under "how to" because, as the member name implies
, I am no expert, just wingin' it! However... I was searching for fiberglass roof sealing and did not find much clarity, and I THINK I have come across some great info, that others may benefit from.
I have a 1991 Ford E350 shuttle bus. The roof was a really lovely garden. I scrubbed it off and was left with a textured fiberglass roof that was ok structurally but had a few issues. One, the designer geniuses made the roof such that the sides round up, and there is a middle panel that creates the top of the bus. This panel is RECESSED under the sides. Read: nowhere for water to run off, it must pool at the low pointsand evaporate- or leak under the seam into the bus. Awesome. Plus, there are metal rivets all around the top that tend to leak. Because of this obnoxious design, and the desire for better cooling/ insulation, I wanted to put a roof coating on. And, I did not want to spend much money.
The "not much money" part lead me to Kool Seal, an elastomeric coating. But the info for fiberglass was limited and confusing (it says "for metal, asphalt,..., not specifically fiberglass) and the reviews are mixed (not just for Kool Seal; there were cranky people who had unsucessfully used other elastomeric products on fiberglass as well). Some people used it and loved it, said that many years out it was still great, others said it was a peeling mess and to never, ever use that product. Some people said no primer needed, just clean the roof and put the coating on. But some people- and, actually, the successful people- seemed to stress the importance of the primer. That makes sense; the peeling isn't really the product, but is the lack of bonding with the fiberglass.
So I went to a local store that had Kool Seal- but didn't have the Kool Seal primer. I noticed that it was a Sherwin Williams product, so I called them to see if they carried the primer (the regular Sherwin Williams store did not, the "commercial" rated Sher Williams store did). But, in talking to the Sherwin Williams guy, once he heard that it was fiberglass he told me to NOT use the Kool Seal Primer- that a good primer is absolutely essential, but the Kool Seal primer is made for metal or asphalt, and does not have a strong enough bond for fiberglass (I had been so irritated that the first store didn't have the primer, you know how it goes, I want to do my project NOW- but thank goodness they didn't have it because I would have just bought it and not have gotten this vital info!). He said that by far the best primer is called UMA (urethane modified acrylic) by a company called XIM.
He said that unfortunately, they (Sherwin Williams) no longer carry that primer, and that he cringes to send me to a competitor but he sees that Kool Seal is a fantastic product but people don't have success with their project (and Kool Seal gets bad reviews) when they do not do the proper prep. No primer, or the wrong primer for fiberglass, can be a disaster. So he sent me to Rodda or Miller, who do carry it (my local Rodda store didn't, but Miller did- about $47 for a gallon). I asked the Sherwin Williams guy if, in case I could not track the UMA by XIM down, does he have a second choice that I could use. He said yes they do have a modified acrylic primer product, as do other people, but he said that searching out the XIM UMA was worth it, "the bee's knees", nothing else comes even close to how well it bonds with smooth surfaces like fiberglass, and you really don't want to have to do this again. ("But come back and purchase the Kool Seal from us!"). Well, OK!
With that kind of recommendation, even about a competitor's product, I feel pretty darn good about setting my Kool Seal project up for success. It makes sense that, like always, it's all in the prep- and that you can't expect any elastomeric compound to bond well directly to fiberglass without primer- and, much preferably, the right primer for fiberglass!
One last thing- I was pretty excited to do this today, prime in the morning, apply Kool Seal tonight, woohoo! But I happen to read that it is dry in 4 hours but takes 7-10 days to fully cure. I figure, great, it'll just cure under the Kool Seal. But I checked with the guy at Miller to make sure. He was horrified! He said NO NO NO, don't ever put a top coat on until it has fully cured; it's the biggest mistake people make- it's dry, so they put the top coat on, and it never actually cures and therefore never fully bonds to the fiberglass. Oh. Bummer. So... I'm NOT finishing my roof today... or this week?!
But, I'll gladly do what I need to do it right, because nobody wants a peeling mess, or to do this all again!
He (Miller Paint guy) said that one good coat should be fine if I made it thick. If I wanted to do more, to do touch-ups or the second coat, it is fine within an hour or two but don't go beyond the 4 hour time unless you want to wait the full 7-10 days before a second coat. I had more than half of the gallon left (after covering about an 18 x 8 ft roof area) so I went ahead and did a second coat, but I agree, it probably didn't need it.
I can't give you the "this has lasted me years and years" assessment, but I can say that I feel pretty good about where this is headed, thanks to a lot of luck (no primer at the first store, getting great customer service guys, asking what turned out to be vital questions...!). Hope this helps someone!
Any suggestions or comments are welcome. Thanks for all the help I've found at this site.
Happy adventuring, everyone! (That is... adventures in going places in our busses, and, adventures in working ON our busses!)