Old fender repair, info please? - ZR-1 Net Registry Forums

conesare2seconds · 01-20-2020

Is there a trick to making a fender repair last?

My car had a fender cracked years ago with a prior owner. Although the paint is nice, I could see the repair underneath and had it redone. The body guy said the first shop used cheap filler and he had the material to do the job right, etc.

Fast forward a few years and I can see the repair work again. The old crack isn’t visible, but the skim coat is showing imperfections I didn’t see when the panel was refinished. I kept an eye on the repair as it was done and the panel seemed well finished before paint.

It’s something I’ve observed with other C4s, too - over time, any filler seems to keep shrinking and though smooth at first, eventually shows through the finish.

What’s going on and is it inevitable? Was the repair just not done properly again? Am I going to have to track down a whole fender and have a replacement bonded in?

lfalzarano · 01-20-2020

I have never heard of filler on fiberglass Corvette unless it is resin and fiberglass mat. I did my 68 427 and it never cracked after primer and painting.

Sent from my iPhone using ZR-1 Net Registry

Carnutdallas · 01-20-2020

Shrinkage due to material differences. Extremely hard to do right. Practically impossible unless you prep, repair and wipe the entire panel. I own a Collison center and steer away from Corvettes, even though I own 4 of them, LOL.

Sent from my iPhone using Tapatalk

Flyman 27 · 01-21-2020

That would happen if they used a fiberglass resin to make the repair.
A C4 is made with a SMC resin which is not compatible with standard fiberglass resins.

lfalzarano · 01-21-2020

Quote:

Originally Posted by Flyman 27

That would happen if they used a fiberglass resin to make the repair.

A C4 is made with a SMC resin which is not compatible with standard fiberglass resins.

Didn’t know that... Fortunately I don’t have a need to repair the fiberglass on my Z!

Sent from my iPhone using ZR-1 Net Registry

fred · 01-21-2020

Quote:

Originally Posted by Flyman 27

That would happen if they used a fiberglass resin to make the repair.
A C4 is made with a SMC resin which is not compatible with standard fiberglass resins.

C4s require SMC compatible resins, epoxys and fillers to get the "bite" needed to make repairs and be able to feather edge the repair. I've had better luck using epoxy adhesives in place of resins. Always use epoxy primer/fillers, and use matt instead of mesh or screen. C4s were the first generation to not use bonding strips to join panels, but hid the joints.

billschroeder5842 · 01-21-2020

Quote:

Originally Posted by fred

C4s require SMC compatible resins, epoxys and fillers to get the "bite" needed to make repairs and be able to feather edge the repair.

This is 100% spot on. Last year I had a small fender bender that required some work on the hood. The insurance company was willing to pay for cheap fiberglass/bondo materials while my shop insisted on SMC compatible products.

Eventually the insurance company caved and my hood got repaired the correct way.

conesare2seconds · 01-21-2020

Thanks for the info. The old crack repair isn’t visible, but the glaze coat that was used to feather in the repaired area shows through the paint now. Looks like I’ll have it re-done.

01-20-2020	#1
conesare2seconds Join Date: Jul 2016 Location: Greater St. Louis Posts: 483	Old fender repair, info please? Is there a trick to making a fender repair last? My car had a fender cracked years ago with a prior owner. Although the paint is nice, I could see the repair underneath and had it redone. The body guy said the first shop used cheap filler and he had the material to do the job right, etc. Fast forward a few years and I can see the repair work again. The old crack isn’t visible, but the skim coat is showing imperfections I didn’t see when the panel was refinished. I kept an eye on the repair as it was done and the panel seemed well finished before paint. It’s something I’ve observed with other C4s, too - over time, any filler seems to keep shrinking and though smooth at first, eventually shows through the finish. What’s going on and is it inevitable? Was the repair just not done properly again? Am I going to have to track down a whole fender and have a replacement bonded in? Last edited by conesare2seconds; 01-20-2020 at 08:49 AM.

01-20-2020	#2
lfalzarano Join Date: Feb 2011 Location: Clayton, North Carolina Posts: 1,133	Re: Old fender repair, info please? I have never heard of filler on fiberglass Corvette unless it is resin and fiberglass mat. I did my 68 427 and it never cracked after primer and painting. Sent from my iPhone using ZR-1 Net Registry __________________ Lou[COLOR="Red"][B][SIZE="4"][/SIZE][/B][/COLOR]

01-20-2020	#3
Carnutdallas Join Date: Oct 2019 Location: Dallas Burbz, TX Posts: 23	Re: Old fender repair, info please? Shrinkage due to material differences. Extremely hard to do right. Practically impossible unless you prep, repair and wipe the entire panel. I own a Collison center and steer away from Corvettes, even though I own 4 of them, LOL. Sent from my iPhone using Tapatalk

01-21-2020	#4
Flyman 27 Join Date: Apr 2017 Location: Wayne Illinois Posts: 396	Re: Old fender repair, info please? That would happen if they used a fiberglass resin to make the repair. A C4 is made with a SMC resin which is not compatible with standard fiberglass resins. __________________ 91-#1935 Black/black & gray, Haibeck 500 Cams by Pete

01-21-2020	#8
conesare2seconds Join Date: Jul 2016 Location: Greater St. Louis Posts: 483	Re: Old fender repair, info please? Thanks for the info. The old crack repair isn’t visible, but the glaze coat that was used to feather in the repaired area shows through the paint now. Looks like I’ll have it re-done.