Painting plastic bumpers

[Jack155Q4]

I will be spraying the bumpers of my car this weekend (I hope)

Some of the original paint had flaked off (ex. 2x2cm) in some areas after scrapping it on a kerb.

How should I prep it? Same way as the bonnet and feather them out with a 240 DA. Then hand sand the rest with P600?

The paint in most areas is good so do I need to primer it all?
I have some a plastic primer aerosol - I assume I only use this on the bare plastic?

Many thanks,
Jack

 

[Raf]

prep pretty much the same; use your common sense as to which paper you select but remember that plastic and metal are different; you can scratch plastic much easier and cause damage. use a DA by all means but treat it like plastic and not the bonnet. if you are not skilled with a DA its very easy to rub away the plastic along with the paint. esp on edges.

finish with P600 _ P800 is fine. P800 is what i finish too.

no need to primer all of it but its easier painting basecoat over a single colour ; esp if you are new. if you primer only sections then on your first coat of base spray the primed areas only; that should get you a more even colour over the whole bumper for subsequent coats.

i usually plastic prime the whole bumper but the key is getting it on exposed bare plastic. this is the first step before other primers.

 

[Jack155Q4]

i usually plastic prime the whole bumper but the key is getting it on exposed bare plastic. this is the first step before other primers.

Many thanks, great reply. Could you just clarify; you would plastic prime the whole bumper painted and bare plastic areas? With the emphasis of getting it well on the unpainted bits?

 

[pedrobedro]

It's very easy to melt plastic with the DA if you don't watch what you are doing very carefully, it doesn't dissipate heat very well as we found out on some door handles.

 

[Jack155Q4]

Might stick to hand sanding then...thanks.

 

[steveo3002]

id only plastic primer the bare plastic , if the rest is good paint then sand it up and paint it , if the rest is poor then high build over it all as req

 

[Raf]

Many thanks, great reply. Could you just clarify; you would plastic prime the whole bumper painted and bare plastic areas? With the emphasis of getting it well on the unpainted bits?

yes and yes....

 

[Jack155Q4]

Cheers.
So one would plastic prime all and one only the plastic areas. I might just do the whole spoiler and see how I go and maybe revise this when I get to the bumpers.

I started on the spoiler yesterday. I gently DA sanded a couple of areas where the paint has lifted. I then took P600 wet to the whole thing including the already DA'd area. Now I will plastic prime all, filler prime and paint. I am worried about the low points created by the DA'd area - not sure if I will see these - is this where a guide coat comes in?

 

[Drew 13.]

Is that not what high build primer fills in, the areas that you have feathered back with the da?

 

[Jack155Q4]

I'm not sure - I guess if the lowest point is 0.5mm lower than the rest of the panel and I spray a coat of high build and for (extreme) example it made a layer of paint 1mm thick would the low point not still be 0.5mm lower than the rest?

How do you get an absolute flat surface?
I would think you would need to sand down the rest of the panel to the level with the lowest point.

Or is high build better than that and does indeed fill it in?

I am not sure yet how much the eye can see in these differences once the paint is on?

 

[Raf]

i would work the edges better and take all the shine off the spoiler. (this helps paint stick better and also avoids runs on the edges).

spray some high build primer on it (after the plastic primer); you could spray 1-2 coat on the worked areas, then a coat or two on all but really you wont be able to tell as long as the areas are feathered (like they are). high build (2k) is errr high build and would certainly level that out.

then onto guide coat and flatten; this will show any unevenness. you will need to use a hard block if you're looking for a flat finish. sand in straight lines and cross hatch pattern.
fill any low points with something like topstop or final finishing putty. (i dont think this is necessary for this spoiler).

but i think once you get your high build on and sand that down you'll be happy. you wont see the repaired areas. let the high build dry thoroughly before adding colour (see tech sheet).

you can just add high build to the worked areas alone but again for the sake of a few extra strokes i'd do the lot. on a larger panel i would only use high build on the repaired/worked area only; feather that then onto the colours etc.

make sure there is no orange peel before you start the colour. get it flat and then the rest will lay flatter.

hope that helps

 

[Jack155Q4]

It does, many thanks!

Will post my progress with it.

 

[Drew 13.]

Well I did a spoiler with similar damage on the edge as yours and just put two coats of 2k high build, mixed primer, hardener but no thinners. It seems to have filled in the feathered edges now I've covered it with a dark blue clear of base.

 

[Jack155Q4]

Hi guys,

I painted one of the bumpers yesterday in primer and I posted a pic on a car website. They say I should have used an additive to give it more flex on the plastic. I also saw it mentioned on the primer data sheet:
http://www.kapci.com/Portals/0/KAPCI Coatings/Cars TDS/English TDS/Kapci 625 2K Filler.pdf (Adflex 616)

Am I likely to have problems seeing as I didn't and am not planning to for the colour?

 

[langy]

Yep you should use the plasticiser additive if its a flexible bumper.

Hi guys,

I painted one of the bumpers yesterday in primer and I posted a pic on a car website. They say I should have used an additive to give it more flex on the plastic. I also saw it mentioned on the primer data sheet:
http://www.kapci.com/Portals/0/KAPCI Coatings/Cars TDS/English TDS/Kapci 625 2K Filler.pdf (Adflex 616)

Am I likely to have problems seeing as I didn't and am not planning to for the colour?

 

[FranV8]

I think the jury may be out on plasticiser additive. Last time I bought some paint (cellulose) the guy said not to worry about it - modern paint was good enough not to flake off at the first sign of trouble. I guess given he could have sold me some makes me a bit happier with his advice.

I painted a bootlid (steel, badly) and a backpanel (plastic - better job).

 

[langy]

One thing to learn is don't listen to the guys in the shops, they ain't painters !!! If they were they would be painting for more money.

I think the jury may be out on plasticiser additive. Last time I bought some paint (cellulose) the guy said not to worry about it - modern paint was good enough not to flake off at the first sign of trouble. I guess given he could have sold me some makes me a bit happier with his advice.

I painted a bootlid (steel, badly) and a backpanel (plastic - better job).

 

[steveo3002]

ive always only used plasticiser on spongey plastics ..anyone remember mk3 xr3i had really soft ones

normal 2k is flexi enough for the average modern bumper , try it on a test card you can bend it double and leave a crease in it without a crack

having said that theres no harm in it , some say it helps with stone chips

 

[Jack155Q4]

I held off spraying top coat on the bumpers until I speak to the supplier tomorrow