I’m not saying the JP202 will be a problem but my experience of a
similar high build primer was that it suffered significant blistering
when only about 5 years old. It’s not really a problem for the auto
boys because who keeps a car that long?

The issue is the filling medium used in the primer;- Talc or chalk
are bad;- water enters the plastic due to fick’s diffusion where it
mixes with the chalk = carbolic acid which neutralises by drawing
in more water + generating pressure (osmosis) which pushes up a
blister.

As a result of this I currently would fill surface with chemically
inert filled (alumina/kaolin) epoxy or polyester, untill defect free
and then use a standard white 2 part primer.

Fraser

So what chemically inert primer would YOU use?