wrote:

All steel doors are not the same, nor are their cores. The same
with
fiberglass. The skins on both steel and fiberglass vary quite a bit
in thickness as do the composition of their cores and their
respective
"R" ratings.

Gullible me.

Here I thought they would all use a standard urethane core.

Fiberglass can present its own problems with adhesion, and with
latex
finishes, no matter what the manufacturers say, I have always had
problems with adhesion in high traffic areas.

Time for the marine finishes.

High build epoxy primer followed by some good L/P which can be applied
with a mohair roller and tipped with a good brush.

Lew