Probably my biggest concern with my entire build revolves around glue strength. Early on I had some issues with epoxy bonds not being good. Since then, I’ve gotten better, but…
More recently, I’ve been using PL Premium (construction adhesive) for much of my skin to frame joints. I feel that the glue will not be exposed to immersion, the entire thing will be encapsulated in epoxy and cloth and that I should be getting a good (if not better than my epoxy skills) bond.
But… there is still that doubt.
The most common failure I was seeing with my early epoxy work involved the fact that the MDO I am using is pre-primed. The paint they used is really tough… it stands water just great, doesn’t scratch… it’s just like a rock. But there were times it seemed to let go from the underlying rosin impregnated paper that is the facing on MDO.
In my recent skinning work I’ve been sanding off the primer with a quick pass with an angle grinder with a 36 grit sanding wheel on it. That removes most of the pirmer and gets us down to paper quick like.
As a test, last night I laid up three scrap pieces of MDO, primer and all, and glued them together with some screws providing clamping pressure. This was with PL Premium. Tonight, I attempted to separate the joint. This was with just barely 24 hours cure.
If you look closely at the picture, at the top you will see some greyish brown areas that are a place the primer let go of the rosin. For the majority of the distance, the laminations of the plywood split before the glue thought about letting go. The difference in the sections was the clamping pressure… there wasn’t much at the top.
This both makes me feel good that the glue is doing well, and that the primer probably isn’t a real weak length. It also shows me that I need to be serious about clamping/screwing.