Here is the Cause of fiberglass checking

[RUn2it]

I have seen lots of posts about the fiberglass checking and thought I'd share what I found. I have an old 1994 Holiday Rambler, sides are laminated aluminum to Luan so the end caps is where I had the problem, it started in the area that was painted dark grey as most have noticed the problem starts with the darkest color and eventually spreads. I decide to eliminate the stripe and paint front cap all white, sand/primer/paint. After a couple heat cycles (day/night/day etc) I see the cracks again so I take a cordless drill with a 1/8" shank small "egg" porting tool and make shallow grooves over cracks/composite filler/sand/prime/paint and the paint lasted a couple weeks till I noticed the cracks again. Every time I walk by I hear cracks giggling and whispering amongst each other so I get the cordless and the egg porting bit and go to town, I decide I'm grinding till the crack disappears...... guess what I found... a small pocket about the size of a BB, was an air pocket that was from when they made the cap. Make sense? If you have air trapped and the cap was made in someplace like Indiana and inside a facility how much expansion would there be if glass was painted black and you're at Lake Havasu on the July 4th weekend at 117 deg? Not a problem with aluminum sidewalls, my problem was treated luan laminated to Aluminum and luan gets damp and the chemical has a ph to the extreme end of scale, either alkaline or acid, and along with whatever is in the adhesive causes corrosion from the back side, pinholes, and use whatever product you think will stop it and it keeps coming back. Was going to use Filon to reside but decided on new plywood I will seal in epoxy resin, bead blast the corrosion and use an aluminum composite to repair corrosion, re-hang the walls and primer then wait. If no pin holes re-appear I'll paint WHITE. Hope this is still relevant and helps those to at least know why it happened in my case anyways, many were getting close recognizing it started with black painted areas 1st. Have fixed many things since I have put 180,000 miles on this RV, a fair amount on dirt, even dunes but have to air down to 50 psi. Lee


Edit: actually about 145,000, it had 35 when I bought it, just keeping it true.

[RUn2it]

Might as well throw this out also, if you have the fractured gel coat don't compound or buff with light colored compound/glaze, it will build up in the cracks and look like this pic from another thread. Lee

[Route 66]

The luan substrate has been the cause of many sidewall problems.

I believe the switch to C-Tek sidewalls has eliminated the problems, or at least greatly reduced them.

[Luv2go]

We had Newmar replace the bad laminated sidewalls on our coach.

I would not be surprised if the mechanism is similar to what RUn2it is describing, gas buildup from the bad lamination job causing the checking.