Auto body repair & detailing: bumper paint peeling, plastic bumpers, adhesion promoter

Question
We recently had some minor rear-end repairs done on my daughters 2000 Rav 4. (less than 3 months ago)The corner bumper was replaced and newly painted. She recently backed into and scraped the edge of a tree. The damage was very small,not even a dent. But where there should have been a scratch the paint is cracking and peeling away all over the bumper. It appears that the entire bumper paint will need to be redone since it will all peel off. We contacted the body shop who told us that all plastic bumpers that are re-painted do this. Is this true? We suspect that it was not properly prepped. The black surface underneath is quite smooth with no evidence of sanding. Should this have happened?

Answer
Hi Leslie,

Sorry for the delay in answering.

Should this have happened? No.

Is this really common? Yes.

Plastic parts, by nature, are hard to get paint to adhere to. The main reason is that THEY flex and PAINT (generally) does not.

This problem is especially common in Toyota and Subaru bumpers. They are supplied in a raw plastic form, with no factory primer on them. The plastic is also infused with a release agent, which keeps the part from sticking to the mold at the factory, but also makes it that much harder to get paint to stick to.

The shop that I am employed by uses a special pad made by 3M containing a cleanser and an adhesion promoter on these bumpers. This usually takes care of the problem.

The fact that you're not seeing evidence of sanding doesn't mean they didn't SCUFF it. This is done with a lightly abrasive pad and only leaves VERY light scratches in the plastic, and should usually be sufficient. A plastic part shouldn't be "sanded" unless absolutely necessary, it opens up the plastic and allows the paint to come into more chemicals within the plastic which can cause problems with the paint "reacting" with the chemicals.

Now to the body shop. Unfortunately, most or all body shop warranties expire the INSTANT that their repair comes in contact with anything it shouldn't. That doesn't mean, though, that the shop shouldn't have some mercy on you. I think in this situation my shop would probably take care of it...we could probably get our paint supplier to cover it.

It might not hurt to ask them what kind of adhesion promoters they use, and what they do to remove the release agents from the plastic prior to painting.

At the very least, I would think the shop should be willing to split the cost of repairs with you.

I hope this information is of some use to you. If you have any other questions, please don't hesitate to ask.

Good luck and have a good day!

Aaron