Geoff Mills wrote:
On Sat, 13 Jun 2009 14:37:13 GMT, Stuart Noble
wrote:

Geoff Mills wrote:
I know paint technology is a complex science but I usually get away
with it. However, I've been tarting up a pair of old Wharfdale
speakers with spray paint to match the existing grey and black kit and
the finish coat is causing the underlying primer to bubble up on a
small test area.

The primer is "Plasti-kote, Projekt Paint, Primer SUPER" which I
bought from B&Q. I have also bought some Simoniz Acrylic Black as a
top coat. Neither cans give specific details about their chemical
composition but they sure enough don't like each other.

I'm hoping someone can tell me of an intermediate neutral coat I can
apply to avoid having to strip the whole lot back to stage 1.

IME bubbling is usually caused by trapped solvents in the basecoat i.e.
the surface cures and stops the carrier (water or solvent) evaporating
from the lower layer. Thinner coats are usually the answer.

Thanks, I'll observe the thinner coat principle in future.

It's usually faster in the long run too, a thin coat drying in less than
half the time of a thick one IYSWIM

This job, being at the stage it is, would leaving the speakers in a
warm airing cupboard for a few days drive off enough of the primer
solvent to allow the finish coats to then go on without the bad
reaction?

IME no. You really need to get back to the point where the basecoat
solvent can evaporate normally, which may not be all the way back to the
original, but probably close to it. You can usually tell when it's ok by
sanding a patch with a fine paper. If the coating has cured, it should
sand to a powder with no gunk sticking to the paper.
I could be wildly wrong about all this of course, but surface coatings
rarely react with each other unless the topcoat contains a volatile
solvent (e.g. Hammerite)