gbarmore

In the process of stripping paint off my car to get ready for a fresh color / clear, but have no idea how to safely remove paint from the urethane front and rear bumpers. I tried the SEM urethane paint remover but it does nothing to remove the original OEM finish (Guess I need to find a new body shop because they told me this was the right stuff).

Anyway, is this a simple matter of sanding them down, and if so how far do I go with it, just to primer and stop? I've heard that getting new paint to stick well to the bare urethane is a crapshoot at best. Do I primer these just like the glass parts? I've heard that a flex agent should be added to the paint to help keep it from cracking, is that advisable / necessary?

Is any special primer required for Urethane that might have old primer still on it?

Any help is greatly appreciated as usual!

mark79,80

I would not use a chemical stripper on them, even one for urethane bumpers. I found they can permanently stretch and deform the
bumper. They also do not effectively remove urethane primers.

I have used a DA with 80 grit paper to remove most of the paint
and hand sand the hard to reach areas.

I would strip all the layers of paint that show any cracking or
other defects.

I have also found on some bumpers that the cracks are actually
in the urethane in which case I replaced them.

Regarding priming, if the bumper is new I first use Bulldog brand
sanding soap to prep them, followed by Bulldog brand adhesion
promoter and then several coats of PPG epoxy. It states in
their information sheet to use the slower acting catalyst on
urethane parts. I then lightly water sand any orange peel, spray
another coat of epoxy mixed as a sealer, followed by
color and clear. I have been using their flex additive
in the clear, as I have been painting them off the car.

On used bumpers where some filling is needed I use several coats
of PPG urethane primer and water sand with 600 paper. Follow
with one coat of epoxy mixed as a sealer and then spray color
and clear.

I do prefer to paint them off the car as I can paint all the edges of
the bumper and the edges of the car. If I paint them on the car
I loosen them so a gap is between the bumper and the car to enable
painting the edges. This also prevents the paint from filling in the
gap between the car and bumper.

I am not a professional but all the bumpers refinished this way have held
up very well.

gbarmore

Very helpful Mark, thank you for the thorough description of your process. My bumpers are in very good shape. Wondering if I might be better off just scuffing them and then going through the priming and color / clear steps you mentioned? Any thoughts on that?

I'm not worried about the amount of work to sand them, just wondering if I would maintain better adhesion if I scuff whats there vs. taking down to the urethane.

Much appreciated!

mark79,80

Depending on how much paint is already on them, if you only scuff them
before painting there may be too much paint on them when finished.
This may lead to the paint cracking. I know it is more work, but
with bumpers I sand at least the clear off and some of the color.
After the rough sanding I use the remaining paint to level the surface
by block sanding. I then use epoxy mixed as a sealer before applying
the color.

I know there are professional painters on this site and they may
have some better insight.

Dave Tracy

You will likely need to add the flexible agent to the primers and paint.

gbarmore

Mark, my bumpers have the original paint on them so no clear coat, just the coat applied by the factory. I'll knock it down as much as possible to give the new primer / paint something to grab on to and see how it goes.

Dave, I'm glad you said that about adding flex agent to primer, was wondering about that. I figured if the primer doesn't flex, a flex agent in the paint isn't going to help a lot.