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Author Topic:   Cowling Paint Problem
Kolbert posted 05-06-2003 08:24 AM ET (US)   Profile for Kolbert   Send Email to Kolbert  
I am refurbishing the cowling on a Johnson outboard and have had problems with the paint cracking in one area. The cowl was repaired in this one section with epoxy and then sanded and primed. The main section of the expoxy repair has been fine, but the small sections just off the side of the repair, where the overlap expoxy was sanded off, have developed small paint cracks. A re-sanding and re-priming have still resulted in the same problem. The prime and paint were done in thinner coats on the second go-round. Any thoughts or tips on how to solve this problem?
bsmotril posted 05-06-2003 10:25 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
There is probably different thermal expansion rates between the two materials. Is the cowl metal or fiberglass? Might want to try a different repair material closer to the original cowl material.
BillS
captbone posted 05-06-2003 10:45 AM ET (US)     Profile for captbone  Send Email to captbone     
The easiest way, I can think of is just to get a different used hood. Walk around the big marinas and they will have a pile of new and old hoods for pretty cheap somewhere in the yard. Most can be had for 100.oo dollars
Kolbert posted 05-06-2003 12:14 PM ET (US)     Profile for Kolbert  Send Email to Kolbert     
The cowl is fiberglass. I am perplexed by the paint cracking only on the edge section where the epoxy had been sanded off. Is the fiberglass an epoxy based material or is the hardener something different?

bsmotril posted 05-07-2003 09:33 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
If the epoxy was a body putty material, then the filler used may be a source of the problem. Some require use of a specific primer paint over the filler before the top coat is applied. If plain old epoxy was used, the "amine blush" from the cured epoxy must be thoroughly cleaned off before applying paint. Sanding alone does not do this. Fiberglass uses vinylester or polyester resins which are different than epoxy resins.
BillS
Kolbert posted 05-12-2003 04:13 PM ET (US)     Profile for Kolbert  Send Email to Kolbert     
I took everyone's advice and stripped the cowl back down and repaired it with a fiberglass patch, primed and then repainted. Problem still exists and if anything, it is worse. I let the primer dry over night before proceeding. There are spider cracks on most of the edges of the primed section. This is the 3rd time that I have done this process and I am at wits end.

Do I need a special primer? Does the fiberglass patch need to be specially cleaned before applying the primer? Does the primer need to be specially cleaned before painting? Should I run over the cowling with my car to save my sanity?

Thanks, Austin

bsmotril posted 05-12-2003 09:45 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Is the primer you are using formulated to be used with the top coat? If it is, and you cleaned the surface, then that should rule out bond failure. That leaves only two real possible causes then;
Mechanical movement of the repair causing paint failure

or incorrect painting technique causing the primer to soften and check.

If the first might be a possibility, an added patch to the inside of the cowl would help stabilize the repair.

For the latter, use sweeping strokes, don't hold the spray too close, and use multiple thin coats letting the paint dry between each coat. It will take many coats to get complete coverage. Don't try to do it all in one coat, or that will soften the underlying primer. Apply the primer the same way, many thin fine coats until you get coverage.
BillS

Bigshot posted 05-13-2003 11:05 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
before you drive over the cowl remember this old saying. "Laquer over enamel will crack her". Tempo paint is laquer. If primer is not cracking, it is obviously your topcoat that is not compatible with the primer.
Kolbert posted 05-13-2003 02:51 PM ET (US)     Profile for Kolbert  Send Email to Kolbert     
BillS and Bigshot, thanks for the guidance. I just looked more closely at the cans of tempo paint and the primer. Bigshot, you are 100% correct, enamel primer and tempo laquer. Just purchased a can of white laquer primer to put this whole episode to bed.

Bigshot, another quick question. Do you know if the cracking would show up right away or over time? The reason I ask is, the whole cowling was primed with this enamel and then sprayed with the tempo, without any cracking. As I was finish sanding the piece, my butter fingers let the cowl slip and the fall cracked it on the corner. Hence the repair and my previously descripbed problems.

Thanks again for your help.

Happy Boating,
Austin

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