Paint source.

[john.mitchell]

I have repaired a pair of crashed panniers and had to use fibreglass mat and filler to do this. However I find there is a big reaction when I spray it with undercoat or topcoat spray cans. I have done this often before (mainly repairing racing dinghies) and never had this problem. This was all a long time ago and I know paint formulae have changed. I once remember a problem with a mudguard but I bought a neutral sealer spray, oversprayed the offending part and it was fine. it was fine after that.
However I can't seem to find any form of neutral sealer paint any more.
Any ideas,folks?

[brenton.roy]

Hi John,
Fibreglass shouldn't react to paint in itself (famous last words I know..). The two most likely culprits are silicone from previous polishes and mismatched paint types - ie acrylic over enamel.
You can clean wax and silicone off the surface with Prepsol. This is usually available at automotive paint suppliers.
If using a gun, I would add a couple of drops of "Anti Silicone" to the paint. This comes in a small bottle, so I suppose you could wipe it on with a cloth. It's not expensive, and would be worth buying.

If it is the paint types reacting, the idea is to get a couple of very light coats of primer over the area, and let them dry - then slowly build up. If the solvent in the paint wets back to the lower paint, it'll react again, so keep coats light.
Brenton

forgot to write - the resin will probably be waxed (unwaxed is sticky) - so if you have some acetone left over, this would be the first thing to try.

[john.nash]

Minefield.
Cellulose paint reacts to everything; sometimes even itself. I've had mixed experiences with the newer acrylic (water based) stuff doing the same thing.
Synthetic seems more amenable to what it's applied to.
None of it plays well with the ethanol in our modern petrol.....

From my understanding, when new paint is applied it will soften what is underneath, and the solvents react and you get the orange peel effect.
Where the old paint has been sanded back into other layers of old paint then there is more scope for this to happen.....

If too much paint is being applied too quickly, the solvent (in the paint) wont evaporate and is effectively sealed in; waiting to react with the next layer.

The trick is to get the surface as clean of grease and contaminants as possible and then apply the most forgiving of paints in a couple of "mist" layers.
In extreme circumstances, you can get a "bar coat" or isolator paint that effectively plays nice with almost everything.

If it were me, then I'd go the clean and prep route and then hit it with some mist layers of etch primer (although you don't need really need it as it's not metal), as that seems to do well with most things. Living where you do, Mr Mitchell, then GMF in Parkend is your friend; that's their paint place.

[robin.parker]

John, try Autopaint(StHelens), www.auto-paint.co.uk, I bought an aerosol of Barcoat from them last year, did what it says on the can!
Good Luck,
Robin.