Need some guidance regarding painting bumpers. I am using PPG products, but the principles apply to all brands, so chime in if you know the answers.

I am repainting a rear bumper for my 90 Vert, replacing the one that is damaged. When I repainted the car a couple of years ago, I prepped and primed with K36. Topcoated with DCC single-stage. The rear bumper got hit (ok, I backed into my own truck ). I noticed that the front bumper is starting to have some flaking. The primer and topcoat is flaking off the original surface.

I did not use any adhesion promoter or flexiblizer. I just prepped, primed and painted.

What is the right way to do this?

1.) prep, apply adhesion promoter, paint with topcoat +flexibilizer?

2.) Prep, apply adhesion promoter, prime +flex, sand, paint+flex?

Do I need primer? Will the adhesion promoter stick the primer? Does the primer get flex as well as the topcoat?

Do I put adhesion promoter between the primer and topcoat?

The guys at the paint co. will sell me anything I want, but they are not really helpful at recommendations.

Thanks in advance.

 

if the rear bumper has good condition original paint just sand it and paint right over it. If the paint you are using requires a flex additive then use it, but you do not need a adhesion promoter

 

Thanks Rob- The 'new' bumper has the original finish, it is in good shape except the upper surface is starting to fade and there are a couple of scratches that i want to fill before paint.

So I and clean, sand, fill, sand, spot prime and just paint with the finish coat?

do I need to add a flex additive to the Urethane to prevent flex cracking?


On my front bumper the K36 did not stick well. I did clean and use a wax remover. I sanded with 360 grit and then primed with the K36. The top coat is sticking to the primer, but the primer is coming loose from the oem finish.

Suggestion?

 

I dont know k36 so I cant help you there
Most primers will have a data sheet that will specify if additives are required for urethane bumpers or not

Remember that any system when stressed is going to release from the bumper, no different then metal- you bash it hard enough and something is going to give

Usually I do not suggest spot priming unless it is like a few very small spots

 

Yes it is just a couple of nicks-but I want to fill them thus the spot prime. I was planning to prime the whole bumper, but that is what led to my original question-basically how to get adhesion of the primer and increase flex in the primer and paint.

I have had no problem with the K-36 sticking to the rest of the car but that doesn't have the flexible surface since it is metal metal. The K36 was applied over the oem finish after surface prep like I described above-clean, wax remover sand w/320grit and prime. I have fixed a couple of door dings with no issues. That is why I assume it to be an issue with the flexibility of the plastic bumpers.

Do you use a flex additive when you paint the bumpers?

 

my paint is very flexible, I can actually paint rubber gaskets and the paint stays

 

What are you using?

 

Imron

 

When I got to the paint shop, I met a painter who had recently gone to work at the shop part time. They brought him out front to advise me. This is the first time I have gotten any practical advice from the store. Before they would only venture as far as to give me a tech bulletin and let me make my choices. That is why I was using the K36.

He told me exactly the same as you are saying Rob, except he knew from experience that that the k36 primer I was using is too brittle for bumpers. He told me that if I was using a raw bumper that needed priming, there was a better primer that did not need flex additive.

He told me that for repainting a bumper that already had factory paint, just fill, clean, sand and paint. Said that the paint I am using does not need a flex, that it is flexible enough, that I don't need primer since the bumper is not raw.

Gonna give it a whirl tonight.

Thanks for the good advice Rob!

 

no problem, and in the future if you were ever to be offered a new bumper ( for any car ) with primer already on it that is what you want to buy versus raw.
New raw bumpers are tricky to paint, people scuff them and think that is good but there are others who bake them to release the release agents in them and all kinds of tricks.

So if you can get a factory primed bumper or better yet a good condition original paint those are always the better choice.

 

Hey also, once you're actually ready to DIY, go to the place where you plan on buying the paint and talk to the guys and they'll be able to help you out.

Im painting an aftermarket lip for my s2000 and had to get supplies last week and they pretty much gave me the rundown for what I would need. For a clean unprimered part, 400-600 was enough. Just make sure you'll either use an adhesion promoter or a primer that's ready for plastic , SEM makes one.

 

9 years later lol