Paint compatibility on wooden speakers?

[Geoff Mills]

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.

[Stuart Noble]

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.

[Geoff Mills]

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

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?

[Graham.]

How disappointing. I thought this was going to be a question about paint affecting the sound quality. Like what kind varnish to use on my Stradivarius?

[Geoff Mills]

Despite my inadequacies, I rarely fail to disappoint.

Well, it most certainly does. Since this paint job started the speakers have ben unusually silent.

Get you!

[Stuart Noble]

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

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)

[sdhull]

Sometimes just using a different *solvent* can cause a reaction problem when using different paints, even using the same solvent at a later date can cause a reaction problem, especially with cellulose and acrylic spray based paints.

I'm not referring to trapped solvent bubbles here, they are a different problem altogether.

As previously suggested, leave the primer to dry sufficiently before attempting to apply a top coat and when you do, apply a dry coat first which will help protect the surface from over wetting, which is the main cause of solvent reaction as the solvent penetrates the surface underneath.

Stephen.

[Geoff Mills]

There's certainly no powdering effect from sanding ATM. The surface has a slight tackiness to the touch.

I think you're writing from experience and that you're probably right. There are some variables involved though and if anyone here suggests that further drying of the existing coats might prove beneficial, I'll try it in preference to back-tracking.

[Geoff Mills]

My first (uneducated) impression was that the problem was caused by using a paint containing a different solvent.

The effect was more like a sort of granular eruption than bubbles, though if magnified, it might prove to be very small bubbles.

Thanks for the encouragement to move forward instead of back. That's what I'll do.

[Stuart Noble]

I'd say the tackiness is a dead giveaway. You could try a severe rubbing down with coarse wire wool. This tends to pick up just the gunk but leaves a relatively smooth surface, which should air dry quickly.

[Steve Walker]

There are definite compatibility problems between cellulose and some acrylics, so check what that primer contains. You should still be able to get away with it if you allow plenty of time for the primer to thoroughly dry before finish coating - ie: days rather than hours.

SteveW

[Geoff Mills]

You were exactly right Steve, A weekend in the airing cupboard made it possible to spray on a couple of top coats with no bad reaction. The 1 hour drying time written on the can must 've been a minimum.