63 underbody fiberglass repair

[Frank D.]

This is the only "ding" on the underside of my split window and has been there since I've owned it. Apparently a previous owner ran over something or other.

Lord knows, I'm no body/paint guy and I make no pretenses but I will tackle this. What is the best approach for a good match ?

Just lay glass mat over it, possibly in layers and sand it back ?
Or, make a "paste" out of chopped up mat and slather it in there and then sand it back ?

Its not a stress area so I'd opt for a natural appearance over super strength.. Its original late-63 "gray" glass...
Thanks in advance.

[Mark E.]

Re: 63 underbody fiberglass repair

I'm tackling the same issue on my '70, only worse. It looks like a telephone pole rammed into the floor under the seats. Or maybe the front u-joint failed and tore open the floor. In my case, I could see through the damage so I had to remove the carpet and repair the glass on both sides (so far I've only done the inside; work in process).

In your case, final appearance won't be affected much if you just "slather it in" and "sand it back" versus repairing it properly. I encourage you to grind out all of the damage to prevent cracks from reforming. Your damage is near a reinforcement for a mounting point (seat? I'm not a C2 guy) so strength may be a concern. The adjacent mounting point can at least cause local stress and cracking. This means inspecting the upper side and if necessary doing fiberglass work on both sides.

Fiberglass mat is not only the proper material to use but will also blend the best with the surrounding texture. It won't be invisible but won't be terribly noticeable either. If you can wait a few weeks for me to repair my floorboard, I'll share photos on the Forum to help you decide.

[Frank D.]

Re: 63 underbody fiberglass repair

I'd love to see your repair. My damage is just the surface layer and doesn't go through the panel. Cosmetic really.

If I use glass mat I assume I should grind the ragged edges of the damage back to make a rectangle to "lay in" the mat ?
Or, leave things alone to minimize the repaired area ?

[Mark E.]

Re: 63 underbody fiberglass repair

All damaged fiberglass and cracks need to be ground away and feathered. Typically this is more material than originally thought since cracks become visible as the area is worked. No need for a rectangular shape. It's possible the floor is weakened by the damage and cracks commonly grow, so this is more than cosmetic.

[Frank D.]

Re: 63 underbody fiberglass repair

OK. Got it.

[John D.]

Re: 63 underbody fiberglass repair

What's the best way to blend it so it's not an obvious repair. Is there a coating that can blend it in to the surrounding area?

[Mark E.]

Re: 63 underbody fiberglass repair

Check the similar threads below; some good information. From a texture perspective, repairing with fiberglass mat is a good choice since this is the original material. Normally, the mat is sanded to shape. To match the original molded (unsanded) texture, a flush mold can be attached to the bottom of the pan to cover the repair area while mat is added from the inside. The idea is for the mat to be flush with the bottom of the pan without sanding when the mold is removed. I've never done this but watched a buddy do this years ago.

One thread below suggests tinting the resin to match the floor's color, although I've never done that. But even with a perfect resin color, the repair will be somewhat visible.

It can be painted or undercoated to hide it, but of course that's not an original look.

[Harry S.]

Re: 63 underbody fiberglass repair

Every time I tried a repair with the mat fiberglass it came out awful. What I do now is separate the threads and have a pile ready to use. I use a dye with the resin to match the area I am repairing, gray glass, black (tire tub), etc. I do a test mixture to ensure the color is the same. I then use the resin and the threads to fill the area. I do not care if it is not perfect. After it cures, clip the excess threads then sand. There should be no reason to paint or dye if you had the color in the resin close. The white threads will match the original glass around it.

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[Frank D.]

Re: 63 underbody fiberglass repair

I've sanded and feathered the damage back a bit and I'll think about my approach to repair the mess overnight.
I do like the idea of tinting the resin to get a closer match....that may be the way I go..
The screwed up spot is not thru to the interior so I'm not gonna do the "molded" repair.