Discoloration between bumpers and rest of car...

GTI2001 · 10-26-03, 01:25

Hey y'all, I was 3-stepping my black GTI this weekend for winter-3M SMR, IHG and 3 coats of Collinite and when using my worklight to check for dust, I really noticed the difference on paint color on my rear bumper compared with the rest of the car. I have noticed this before in the sunlight, but it seems as if it has gotten worse. I had the front bumper repainted this past spring and it does not have this brown tone to it and is a very close match to the black paint. The rear bumper is very brownish in color compared to the rest of the body. I am pretty sure that when painting plastic with dark colors, there is a quite a bit of color change than when painting the metal body. Can anyone explain why this is so bad and if there is anything that can be done besides getting the bumpers repainted? TIA

Guitarman · 10-26-03, 02:23

From what I've read on paint tech boards, the oem flex additive supposedly is the cause for a slight darkening or tonal change, as these parts are painted separate from the car body. I've always wondered about them also being painted with a different "batch" of paint from what the body receives, because every mix is slightly different, but have never found a yes or no answer to this.

A body shop would usually try to 'blend' into it whenever adjacent panels are painted, to minimize the effect. Other than that, you can only try to repaint and get as perfect a match as possible with the body of the car. No amount of polishing will help IMO.

Cheers.

GTI2001 · 10-26-03, 02:25

I think with the high amount of polishing I have done over the years on the entire car has really brought out the difference in color betweek the bumper and the rest of the car.

Guitarman · 10-26-03, 02:28

FWIW, I have always felt that painted urethane parts respond differently to UV effects, and perhaps this is why many see a change in tone over time, especially when compounding or polishing of the part(s) comes into play.

Not saying it's definitely the case, just a theory I've had.

MBZ 500E · 10-27-03, 12:38

Funny I had the same problem with my Windsor Blue VW after a rough winter in New England. I mainly noticed it on the side door trim and a little bit on the bumpers. What helped was a good cleaner wax and then follow up wax like you've alredady done, not perfect but better.

I never tried claying back then (had never heard of it) and wonder if it would help. I've read that flex agents in paint have a higher porosity which makes it easier for dirt to adhere. Have you already tried claying?

BK1 · 10-27-03, 12:43

My Dodge is the same way--the rear bumper is a darker silver then the rest.

NY detailer · 10-27-03, 06:17

The biggest reason of color difference between that parts is because of the material

the bumper is plastic and the 1/4 panels are sheet metal.
Paint takes to plastic and sheet metal in different ways.

I have seen brand new cars in dealers that have never been repainted and they look like crap. paint is way off, there is nothing that can really be done with it.

Even if the shop blends the 1/4's on a repaint you still will have a color mismatch.

The best way to show this is take some paint, and paint a plastic bottle and a metal bottle and wait for the paint to dry, then look at the color difference.