cracked paint at skin overlap...

[fehdxl]

This is basically a which came first, the chicken or the egg question...

I was thoroughly cleaning the aircraft belly yesterday and the paint was cracked where the skins overlap. But it's worse than that, I picked at it a bit and there was gunk under the paint for about 1/4 to 1/2 inch back. Obviously the grease, exhaust, dirt, etc has worked it's way in there over time.

My question to the experts out there, did having a dirty belly contribute to the cracking of the paint? Or did it crack first and the gunk then worked its way in? In other words, will keeping the belly clean avoid that cracking?

Thanks in advance,

-Jim

[Mel]

Originally Posted by fehdxl

This is basically a which came first, the chicken or the egg question...
My question to the experts out there, did having a dirty belly contribute to the cracking of the paint? Or did it crack first and the gunk then worked its way in? In other words, will keeping the belly clean avoid that cracking?

Keeping the belly clean will not avoid cracking, but it will allow you to inspect and detect it earlier.

[newtech]

Did you fly the plane before painting?

[fehdxl]

Originally Posted by newtech

Did you fly the plane before painting?

This is actually a '66 Bonanza that was repainted many years ago. So yes and no. The paint peeled all the way to aluminum, so both coats came loose.

Is there a technique to help prevent this? Thicker when painting? Thinner?

Thanks for the replies.

-Jim

[Mel]

Originally Posted by fehdxl

Is there a technique to help prevent this? Thicker when painting? Thinner?

Thicker paint is never better. It is heavy and promotes paint cracking. Thinner paint is better, but it sounds like your problem was caused by improper cleaning prior to painting.
It is VERY difficult to get an airplane totally clean once it has flown for a while.

[Rick S.]

Most likely a prep issue aggravated by an area that flexes. Since it was painted awhile ago, the paint chemistry was older as well. The newer mixes have a bit more flex than the older laquers and polys. FYI, if you don't fix it it will continue, the crack will suck up oil and gunk through capillary action and continue to work under the paint until is reaches an area that flexes less or has been preped a little better.