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Paint cracking


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It would be interesting to know what the paint shop did to the cowling before they painted it. I suspect they used a polyester based filler (Bondo) to smooth it out. Polyester will not bond to epoxy and is stiffer so it will delaminate and crack. I’ve found it is best to just lay up new layers of fiberglass/epoxy and blend that in. You can make a comparable filler by mixing cabosil and micro spheres in with epoxy to make a paste, but you might as well use cloth. It isn’t any harder and it gives a better result. 

Unfortunately, it takes a lot more time to do it right. Besides, the service manual is very specific about what materials can be used for cowling repair. I would bet they didn’t use the antimony trioxide either.

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Agree that it's something relative to the repair. I'd take it back to the paint shop. Polyurethane aircraft paint is very flexible (unlike automotive paint) so it can be applied to fabric without cracking.

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That Fiberglas is still moving.  When it moves it cracks. And then the holes Waller out.  You have to scarf out the  repair and blend it back about 2-3”. It’ .120” of 8oz  aircraft fiberglass and structural epoxy Then. Knock it flat, make a .250 hole, countersink it, and prime Then paint. Ours was done 5 years ago, still looks new.  
I think a lot of paint shops spackle body filer into the hole, or polyester resin and some chopped glass, and then re-drill the hole and countersink.  You cant cheat like that.  These guys didn’t even drill a .250 hole and countersink. They put a large washer over The messed up bodywork.  

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