Painting plastic for the first time

Todd Gatman

Promoted Users
Hi all,

My buddy asked me if I would paint his plastic race car bumper. It has been modified and lightly sanded before I got it. I was planning on shooting a reduced coat of epoxy on it and them proceeding with base and clear.

When I got the bumper, the condition is per the photo below. It looks like there is a factory coating that has been partially sanded through. The coating is rough and looks like it should come off before painting because there is no doubt in my mind you will see this. If I do wetsand it off, does adhesion promoter before epoxy become the right procedure?
 

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First get a glass of water and take a small sliver of the bumper off and place it in the water. If it floats it needs adhesion promoter. If it doesn't float then you don't need to apply ad-pro. Chances are though that it will.

Get every trace of old material off. Follow the instructions in the SPI Tech Manual for prep and application. Then follow up with the epoxy as your sealer.
 
I should add that more than likely you will need to prime before sealing it and painting. Use the epoxy (SPI) for your primer. Just apply the ad-pro first per the instructions in the Tech Manual. If you need to apply any glaze do it over the epoxy. If you sand through any where re-apply the Ad-Pro before applying more primer or sealer.

Keep asking questions if you have them.:)
 
Thanks Chris, you help me alot.
So I followed the advice and removed all of the loose material. I called SPI and couldn't get their adpro because they don't have any right now. I went and got some bulldog promoter in a sprayable quart. Applied the promoter and then a coat of epoxy sealer. Bumper looked great. I waited about 2 hours and then applied the first coat of base. It's deltron fwiw. At this point I was happy with it. I waited about 45 min and shot a second coat of base thinking I would be finished at this point. I cleaned my gun and went in the house planning to shoot clear the next day. I came out in the evening to check on things and there were places where it looked like I used paint stripper. I couldn't believe it.
The next day I wet sanded all of this off down to the bare bumper in those areas, applied a light coat of the promoter, waited and epoxied. Things still seemed ok until later. Same thing happened just on a smaller scale. Can anyone help me figure out how to get through this? I do not have the time (or energy) to strip this bumper all the way down and start over again. I have included some photos. The first photo is after the first coat of base. The second one is during wetsanding and shows the extent of the screwed up area. The third photo is where I stand now. There are places around the perimeter of the newly primed areas where the base coat wrinkled underneath the primer. Really frustrated.
 

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removed all of the loose material.
Looks like you didn't get all the old material off. That third picture where it cooked up looks like there was still some of the original coating on it.
Did you take it all off or just what was peeling? You need to get it all off like I said in my first post. Every trace of old material on it needs to come off or you will have happen what you experienced.
 
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DBC is the worst about lifting an edge if you break through. With what you have, short of starting over, sand lightly and spray unreduced epoxy or 2K over the problems areas. As Chris replied above, your original lifting had to come from something left on the bumper to lift. Adhesion promoter is aggressive, and will cause an uncatalyzed product to soften and wrinkle.
 
Looks like you didn't get all the old material off. That third picture where it cooked up looks like there was still some of the original coating on it.
Did you take it all off or just what was peeling? You need to get it all off like I said in my first post. Every trace of old material on it needs to come off or you will have happen what you experienced.
Thanks Chris, Yeah I sanded the entire bumper and removed everything. My paranoia made me super cautious. I feel like the adhesion promoter is reacting with the base coat on the edges
 
Adhesion promoter is aggressive, and will cause an uncatalyzed product to soften and wrinkle.
Agree but if he is doing it correctly the ad-pro goes on first underneath the epoxy. Don't know how the ad-pro would cause anything to lift if you are using it on bare plastic, and it being the first thing to go on. ONly could happen if there is material already there. If there is/was that is the problem.
I feel like the adhesion promoter is reacting with the base coat on the edges
Impossible if you are doing it correctly.

Sequence of repair:
1.Strip all old/existing material on cover.
2.Wash and W&G remover.
Ideally you would prime it and sand it, and re-prime and re-sand if necessary, judging from the halo in your 3rd pic it needed it. That halo also tells me there was old material there.
3. So after W&G, you would apply ad-pro. One coat or two. Always applied light. Over bare plastic only. Wait appropriate time as per instructions on the TDS.
4. Then apply your epoxy either as primer (1:1) or if plastic is perfect apply your epoxy as a sealer.
5. After waiting the appropriate time for it to flash (time varies depending on how you reduced it) then apply your base. Done this way you will not have issues.

Got to get all the wrinked material in your 3rd pic off, or it will wrinkle again there.
 
The third picture is after the repair to the original wrinkle problem, correct? What is wrinkling now is the base coat edge. Agree there is no way bare plastic can wrinkle. Possibly, the first problem was spraying the bulldog (never cared for it) too wet and applying the epoxy before it flashed good, trapping solvent that eventually made it lift. The worst thing you can do to a lifting problem is try to rush the repair. Getting it out in the sun to thoroughly dry before attempting anything else is necessary at this point, IMO.
 
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