Firewall Gelcoat Cracking

[dakota]

Started the engine for the first time and let it run for about 20 minutes. While it was running, I noticed what looked like cracks forming on the passenger side footbox. By the time I shut it off and let it cool down it had spider webbed over a pretty large area. The driver's side has a little area, but not nearly the size of the passenger side. Initially hoped that it was just the paint, but took a sander to it and some chunks started coming off. It's definately the gelcoat that's cracked and is flaking off. Has anyone else had this happen, and how would you fix it??

I could probably sand the gelcoat completly off in that area, but how big of an area would I have to do to make sure it didn't happen again? Would I have to worry about any subsequent layers of the fiberglass doing the same thing?

Thanks,
Wade

[dscott]

dakota, The only time I've seen any spider cracks are when something is stressing the fiberglass or something has hit it. If you are sure they are spider cracks you can sand and fill them. The way I've seen gelcoat repaired is to use a die grinder and follow each crack to the end, refill with gelcoat, sand and polish. If the crack goes deeper than the gelcoat a new layer of fiberglass would be needed to add the strength back. I would check to make sure nothing is stressing the firewall. The other thing I have seen is air pockets between the gelcoat and fiberglass. This will generally flake off when exposed to heat or stress. This may be the problem. The areas usually look like bumps or pockets on top of the gelcoat. With those you could remove the bad area, regelcoat or use a filler, sand and paint to match. Luckily the area you are talking about is pretty well hidden from view so it won't be as critical visually. Hope this helps.
Don

[Sonny]

dakota,

I'm going to have to note that the floor/footbox was probably sprayed/chopped layup item and when they chopped in the first layer of resin/glass fiber there could have been acetone in the first spray or a bad resin mixture that would resist curing in between the gelcoat, VERY BAD, or it could have been a minus in the catalyst amount in the first spray to a very cured gelcote of a few hours, ever which, theres no cure except grinding it off and painting on matching color gelcote with a 50% catalyst for conditions and laying over the smooth side of commercial wax paper and the taking a broad putty knife and smoothing out the foil/or wax paper to smooth and letting cure. Do not force cure since the catalyst will be at 50% or less, might take several hours. Sand off any rough edges after peeling the wax paper off and polishing with series of course to fine compound. Kinda messy but the most sure fire way of patching a spider/heat crack area. If the glass was good to start with it would not, WOULD NOT, have happened.

[dakota]

Thanks for the replys. I took it off the chassis and took it to CR for them to take a look at. We're waiting for their fiberglass guy to see it. I know it gets EXTREMELY hot there with only 1/2" to 1" of space between it and the headers, but it surely isn't any different than any others that haven't had that problem. I tried "search" and didn't come up with it, but I think there was another post a while back where someone asked about heat affecting the gelcoat and fiberglass. I thought the general opinion was like Don and Sonny's in that the problem is caused by flaws between the gelcoat and fiberglass. The gelcoat should still stand up to that heat without cracking like it did.

In a somewhat related issue......I am thinking of repainting the firewall with trunk paint (black with gray speckles) as opposed to plain black so it doesn't show the dust, dirt, etc. that settles in all those hard to reach places so much. Anybody else used that stuff in the engine bay??
Thanks,
Wade

[Double Venom]

Wade,
I for one will be very intersted in what CR's tells you. Please keep us posted.

You do know the "Speckle" paint you are referring to is NOT water proof?

They do make a clear that will go over it, but in the long run I would be leary of it...Just my 2-cents worth.

DV

[dakota]

I got the firewall back last week. Classic's fiberglass guy took mine and fixed it. Visually it looks to have turned out good.

DV, Pete said that he had talked to you about the lack of clearance on the big block cars. He said that you do some modifying to both the passenger footbox and the fenderwell to gain some additional header clearance. Do you have any pictures?

I didn't know that the trunk paint is not waterproof, and would be a little leary of it for that reason too. I've never used it, just saw it looking through an Eastwood catalogue. Thought it looked good, and the texture and "speckle" might help to hide some of the dust, dirt, scratches, etc. that accumulate over time, and seem to jump out from otherwise great looking engine bays. I might post on the general forum just to see if anyone has much experience with it.

Thanks,
Wade