Originally Posted by sweetwater
By "backside" of the plug do you mean the exposed outer surface and the "internal" surfaces. I'm afraid it would be too late to coat the inside but the outside can and will be coated with something.
Question with using exterior house paint. Should it be used with a primer so that the coatings bond to the wood and are not pulled away from the plug when pulling off the mold?
Do NOT apply that paint on the surface of the mould!!!!
You did already one mistake not to seal the inner sides of your plug (there the paint helps).
The surface was sanded down into the wooden structure (that was another mistake), and should have been immediately sealed by Epoxy or whatever stuff you use for the coating.
Leaving wood open on the backside of your "nice" surface will always end up in a distorted plug once the humidity changes.
ALL the structure of the plug has to be sealed against humidity! So turn it and do that first, you otherwise have a never ending problem.