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Paint Cracking in a few places

Cracks

Hello,

What I see there is shrinkage of filler. Most likely polyester like bondo. Grind, prep and resurface with an epoxy filler to achieve the same height without the poly shrink problems/


Vince
 
Hello,

What I see there is shrinkage of filler. Most likely polyester like bondo. Grind, prep and resurface with an epoxy filler to achieve the same height without the poly shrink problems/


Vince

polyester filler is the standard in auto body repair and has been used on millions of repairs. Yes it shrinks a very small amount in the first 30-90 days and is then VERY stable over time.
What is seen here is NOT filler shrinkage.

That door is likely polyester based fiberglass layup from an old kit. This is crazing/cracking from the polyester based resin becoming hard and brittle as it gives up it's plasticizers over the decades. Pretty sure this is why Vans went to epoxy or vynal ester based F/G parts to avoid this, as those materials don't have that problem.

It can't really be repaired effectively, as it will continue to crack and telegraph through most repair attempts, Unless you can get layers of new cloth over it. Once the parts are dry and brittle, the stability is gone. This is an inherent flaw in thin polyester resin layups; They don't age well.

Larry
 
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I think you're both right, sorta. $10 says it was sprayed with K200, or Featherfill, or similar polyester primer/surfacer.
 
I think you're both right, sorta. $10 says it was sprayed with K200, or Featherfill, or similar polyester primer/surfacer.

Hmm. I'm not sure what the OB (original builder) did in that respect but it certainly sounds plausible.

If it can't really be repaired effectively unless new cloth is in there...are you/Larry saying it has to be sanded down to cloth all the way, or actually cut out and re-fiberglas'd?

-b
 
Hmm. I'm not sure what the OB (original builder) did in that respect but it certainly sounds plausible.

If it can't really be repaired effectively unless new cloth is in there...are you/Larry saying it has to be sanded down to cloth all the way, or actually cut out and re-fiberglas'd?

When you're ready to refinish, slide a knife blade up under a few of those chips. If the chip is thin, the backside is uniform gray or dark mustard, and they pop off the surface leaving bare glass, it's a primer-surfacer problem.

The fix starts with the one fiberglass task I despise, sanding back to bare glass. Anyone know a safe way to remove paint and primer from fiberglass, other than sanding?
 
The fix starts with the one fiberglass task I despise, sanding back to bare glass. Anyone know a safe way to remove paint and primer from fiberglass, other than sanding?
I had to rebuild the fiberglass nose bowl on my C-152. It was cut up real good from from the spinner due to sagging motor mounts, and camloc's that wore through the fiberglass. I had real good luck using the old fashioned Kleen-Strip Aircraft paint stripper,,,(not the newer low VOC stuff they sell now). Doing small sections at a time I was able to carefully monitor the dwell time and get the paint and stripper off leaving solid fiberglass where the paint was.
Still involved lots of sanding to get to the point of patching and re-painting.
 
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