I'm repainting the plastic bumper skirt of my Cappuccino but am having no end of reaction problems. This is now the third time I've had to
sand off paint that I've applied due to what I think are called crows feet.
I cleaned the panel with soapy water then wet sanded it with 400 grit. when it had dried I sprayed it with a polyester spray filler. The paint
seemed to shrink back leaving loads of "cracks" showing the original paint below. I sanded this off and let it dry. Next I tried some
Halfords plastic filler primer in an aerosol. I thought Acrylic might have better luck than polyester. Not much. Anyway, I had another go with some
plastic adhesion primer, which did work a bit better but I still have 2 areas that I've had to sand right back. What do I do?
got me stumped. if pap don't work, i have nothing to suggest
what state is the bumper in, i'm wondering if there could be some wax on it stopping adhesion.
It's not the right thing to do, but you can get past it by building up layer upon layer of dust coats...
I had the se problem on a M/C front fender.
I think i used primer filler in the end, but it never did work too well. I think its something to do with the silicon in the plastic reacting with
the paint.
I know that paint doesnt like silicon, and the smallest amount can ruin a paint shop.
weird
if it is the paint shrinking (for whatever reason) could you spray a few really really light coats (dusting basically) first to allow them to do any
shrinking first, and then once they're on, do you proper colour coats?
also, have you been wiping the bumber with any of those prep cloths first, silicone remover, or thinners first?
Has it had back to black on it or something like that ?
dont wet sand before you paint and dont use soapy water.
adam
Try 'BARCOAT' its a barrier paint that prevents any reaction between layers like silicone impregnation or incompatable solvents.
You can even apply 2k over single pack paints with it.
use a 2k primer and leave it for 2-3days before you go for the base. simples.
Thanks guys. The bumper was in good condition save for being peppered with stone chips. It had been waxed about 6 months ago but nothing more
since.
I've put a dust coat on it and will check put another on in a few minutes. If it looks bad in the morning, I'll go to the paint shop on the
way home from work for barcoat or similar. I'd hoped to be finished already and have a couple of days for it to harden before fitting it back to
the car on Saturday.
Well that didn't go well either. 2 mist coats last night before bed then one in the early hours thanks to insomnia. This morning there are fine cracks where the large ones were yesterday. Jawel paints are not too large a detour on the way home. Lets say what they come up with.
I'd still suspect the wax preventing adhesion. I'd give it a good talking to with a sanding block and have another try.
I'm not expert but hey 
It's not a wax or silicon problem - they cause "fish eyes" not crazing which you've got. Most likely cause is that the bumper has
been painted with someting like an acrylic/synthetic in the past, tho' sometimes reactions just seem to happen for no obvious reason.
I wouldn't recommend the "dust coats" route because you may be fine until you put a final wet coat on to get a shiny finish & will
all happen all over again.
You need an alcohol based sealer, which I believe Barcoat which has been mentioned is an example of. However, to be safe you'll need to seal the
whole bumper, otherwise, your sealer will go on fine, but when you put anything else over the top of it it may well react around the edges of the
sealer coat!
quote:
Originally posted by russbost
Most likely cause is that the bumper has been painted with someting like an acrylic/synthetic in the past
quote:
Originally posted by russbost
to be safe you'll need to seal the whole bumper, otherwise, your sealer will go on fine, but when you put anything else over the top of it it may well react around the edges of the sealer coat!
I am by no means an expert but I have had the problem before.
- Wet sand
- Wash thoroughly with heavy duty degreaser.
- Sun dry ??
-Tack rag,
-Light coat of adhesion promoter
-let dry
-A couple, maybe more thin coats high build primer.
- Key in with 600 grit.
-tack rag,
color
-color sand
Clear coat.
-let dry a couple of weeks,
-polish and wax
lot of work, but must do the trick
UPOL Barcoat is now my best friend. Mind you there were a couple of places where I had to give it a second coat. It now has a coat of filler primer which has not reacted. Hopefully it will stay that way for the rest of the job. Thanks everyone for your help.