Flexibility of Paint

[rmcgann]

G'day all,

I am at the stage of prepping my RV-10 for paint. I am interested in smoothing the joints between fibreglass and skins at various intersections eg wingtips/wing skins, turtledeck/fuse skins etc. I have read that epoxy used to hide the seams is prone to cracking if there is flexing at the joint, and that proseal is more suitable to this task because of its flexibility.

Proseal may be flexible and not subject to cracking on its own, but how resilient is a typical top coat over the top of proseal?

thanks in advance,
Ron
-10 finishing in South Oz

[Rosie]

Here's a tip from Dan Checkoway's website Rosie

[PainterJohn]

Hey Ron,
I have filled and painted over lots of filled joints, both aviation and automotive. Fiberglass is ok, it will crack over time, Proseal is ok too, yet it seems to get soft in the heat, causing the paint to crack. I have been using a 3M product for this application and other applications. I first learned of it as a body man in local dealer ships. it a two part epoxy, and bonds with metals, and composites. It is said to have a peal resistance strength of over 1600 psi, where as a weld connecting two peices of sheetmetal is roughly 900 psi. Fiberglass will peal at around 400 psi, or so im told.
The number on the stuff is 8115 Panel Bonding Epoxy, by 3M of course. There are other versions of the epoxy, some for plastic, pot metal and others. I have found that the 8115 works on just about anything you do not want to ever come loose. If you use this system i have learned another little secret. Grind it, Clean it, Apply it, Let it dry, then heat the area to a temp hotter than the surface can get on a bright sunny day, i usually go around 200 to 250 degrees. The reason for this was discovered in a heated paint booth. When the temps climbed to around 140 for drying the paint on the airplane, the epoxy began to show a "ghost line" every where the glue was. But heat setting the glue prior to any filler, primer, or painting solved this minor issue. And it can be sanded out and primered over, usually with out bondo (which can absorb water and crack and all the other **** that bondo does) Anyway give it a shot, i really like it!!!
Cheers

[dan]

Originally Posted by Rosie

Here's a tip from Dan Checkoway's website Rosie

Thanks Rosie, for the tip on that technique (in case it wasn't clear, I got the technique from Rosie!).

I want to add that after 1250+ hours, the only spot where the gap has made itself visible was where I sanded through that thin fiberglass (bottom of the elevator counterweight arm). Everywhere else, the glass-over-gap has worked great. Just be careful not to sand through that thin deck cloth, and you should be good to go.