A pal of mine is in a bit of a pickle, he's an experienced car body repairer/painter but has been caught out with a job.
Story as follows....

He dropped a bit quiet last summer and with a few reservations took on a full strip and paint of a fibreglass classic car shell, he's no stranger to painting classics, but they are usually steel and not plastic.

As the job progressed it was noted that the gel coat was virtually non existent on many areas of the shell, it turned into a pig of a job and he made sod all money on it due to the time it took to prep, however it looked mint when finished and the customer was over the moon, the shell was taken away and duly built up by the owner.

The chaps now complaining cos there are micro blisters appearing in the paint, and he reckons the bonnet has changed colour, he's obviously wanting it repainting, but my pal is worried it will just happen again, as he felt he had done everything correctly and not cut any corners.

Any advice from experienced fibreglass painters would be appreciated.

Cheers
Al.

If the glassfibre is old it could be suffering from osmosis.

Osmosis in the laminate will resut in large penny sized blisters. Its probably an osmotic reaction between the GRP and the paint film as a result of moisture being trapped in the laminate.

You say that there was virtually no gel coat left. The laminate would probably have been laid up with a cheap orthothalic resin which is not very moisture resistant. If he used Wet 'n Dry n the prep then he should have thouroughly dried the exposed laminate with IR lamps.

The colour change might be due to pigment migration from the remains of the gelcoat. He could try some Barcoat to prevent it happening again.

I've done and been involved in a lot of this type of GRP work. Paint over old and new grp.

There is only one way, bar none, no arguments, to do this properly.

Get onto Marineware in Southampton, and get some Awlgrip two pack epoxy primer.(You'll also need the special thinner.) This is the key part, and a must. This goes onto the BARE grp. You can then put any paint on top of that you want to.

Make sure you leave the primer a day or two to harden before sanding, but not more than five days, as it goes rock hard, and difficult to sand easily. Still remains fairly flexible when fully cured, but harder than granite to sand.

There is simply no better solution.

The bubbling could also be water in the paint, via the compressor, or as above and improperly dried surface.

Cheers,
Nev.

[Edited on 26/1/12 by Neville Jones]

On top of decent gel coat I've used a normal 2k high build primer and 2k top coat . Any cracks etc I grind out completely and build up with layers of resin and glass tissue .