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Flexible sealant for seam in fiberglass roof ???

Posted: Tue Aug 20, 2019 11:54 pm
by nopeda
I have a '68 Lazy Days houseboat with a fiberglass roof. I replaced a section that was rotting, from side to side and about 4 feet from back to front, replacing the plywood beneath and new rafters/joists then covered it with new cloth and West Marine resin. It all cured out very well and I covered the new section overlapping and also covered the old section that was still good to cover spider cracks and it all seemed great. But! After a while the section I replaced being about 1/16" or so lower and tending to flex a tiny bit caused a crack in the fiberglass between the old and new section. I applied more resin and it looked great again. But! After a while there was that crack again. So? Can you folks suggest a dependable flexible product to cover the crack with that will last for years and can be painted over? I was thinking the 3M 5200 through hull caulk might be a good choice. Or maybe White Lightning 3006 40 year caulk. Or are there better products you people can recommend that I have no idea about?

Thank you for any help with this!

Buford, GA USA

Re: Flexible sealant for seam in fiberglass roof ???

Posted: Wed Aug 21, 2019 9:09 pm
by CaptForce
The 5200 can be a functional choice, but not the best permanent fix. I would suggest that you take a grinder and bevel or fare the sides of the crack out to about two inches on each side of the split. If the crack allows the opportunity for resin to drip all the way through, the next step would be to apply a fibrous epoxy filler to seal the opening and trowel smooth on the underside. Then place a strengthening strip or two of fiberglass cloth onto the beveled seam. When this is remaining just a little "tacky" you can fill the remaining dip along the seam with some finishing resin. I used to like the C-flex epoxy for a final coat to paint over. Be sure to sand off the high spots before it cures to form a "rock" and gives you extra work.