: If it is indeed polyester resin, it needs to be sealed from contact with air
: in order for the outer surface to cure. He can probably spray the original
: coat with PVA to accomplish this. I've heard of people using PAM and
: similar sprays, but I wouldn't vouch for their effectiveness.

If the polyester is curing correctly, but is air inhibited, the surface will remain sticky but the deeper stuff will be hard. His description was the other way around. The surface was dried out, but the interior was still "cake frosting". This does not sound like just an air inhibited cure to me.