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[Deuce]

A few months ago I prepped and painted a front and rear spoilers for my Omega.

The front spoiler was GRP gelcoat. I rubbed down, etch primed, primed, paint coats, clear coats, polished, waxed and it looks brilliant still.

The rear spoiler was primed already, although pitted. I used stopper and filler to correct, rubbed down, primed, painted, clear coated, polish and waxed. The finsish was not as good as the front and after a few months had very small spots on it. I just rubbed it down and the raised spots have gone leaving black spots on a now smooth surface.

It must be a reaction somewhere along the line. I used Halfords paint on the front spoiler and with the rear oneI used Vauxhall paint and clearcoat with Halfords primer.

Do I need o strip it back to how I got it or will rubbing smooth and etch primer before repainting do?

[Agemo]

We don't know what paint you used, and even you probably have no idea what paint was there before. You will need to give it a coat of something which will go on any paint, AND allow any paint to go over it. The only name I can think of os BARCOAT, it will let you use it on anything without a reaction, and you can use whatever you want on top of it.

[cem_devecioglu]

if I had to do it, I would sand the surface until bare plastic.. then prime it..

[car5car]

Ask there:
http://www.autobody101.com/forums/viewforum.php?f=16

[razzo]

assuming the spoiler is plastic, not sure why you are using etch primer. Best bet is to flat surface & recoat using a primer or primer filler, etch primer will absorb moisture so if you must use it get a coat of paint on within 20 - 30 mins. I would only use etch on bare metal but epoxy is far superior

some useful info  http://www.carsprays.co.uk/

[Deuce]

Thanks guys. will try and respond to all in one post.

I assumed it is a GRP spoiler but I could be wrong, it had a coat of primer already on it. even though I rubbed it down I didn't find any gelcoat.

It must have been made in two parts as it is hollow to allow for a brake light option, I assume.

I used etch primer as I thought it would seal between the primer already there and what I put on after.

I used U-pol #18 followed, paint coat is VX start silver 3, with VX clearcoat over.

I'll have a read on the autobody and carsprays links.

Thank's 

[Bionic]

Best thing to do is prep it well and then apply a barrier paint like barcote over which you can then put your chosen primer and topcoats. Its always best to use products from the same manufacturer cos mix and match does not always work unless you have pro experience.
It also helps if you download the spec and info sheets for the products you will be using.
 

[Deuce]

I think I need to state that I paint with rattle cans. lol.

I've rubbed the spoiler down with 280 grit, wet, this evening.

The rest I'm taking my time with to make sure all solvents have evaporated between coats and that the room temperature is around 21 C. The spoiler is off the car and I've got some wet n dry paper, 280, 400, 600, 800, 1200, upol #5 filler primer, Halfords silver base and Halfords clear.

Will let you know what happens.

[cem_devecioglu]

I think I need to state that I paint with rattle cans. lol.

I've rubbed the spoiler down with 280 grit, wet, this evening.

The rest I'm taking my time with to make sure all solvents have evaporated between coats and that the room temperature is around 21 C. The spoiler is off the car and I've got some wet n dry paper, 280, 400, 600, 800, 1200, upol #5 filler primer, Halfords silver base and Halfords clear.

Will let you know what happens.

you can use plastic primer as a first coat .. wait some time (but before its completely dry)  then apply normal primer (or epoxy) .. then use wet 800 ..
 
I have used this method on plastic parts with epoxy and it resisted all conditions..
 
this one
http://www.dpc-refinish.com/standoflex--plastic-primer-P319.html
 
http://www.dpc-refinish.com/_doc/tds/STANDOFLEX__PLASTIC_PRIMER_TDS_dflnd_2.pdf