urethane bumpers
Thread Starter
Race Director
Joined: Sep 2003
Posts: 16,838
Likes: 341
From: Database Error Indiana
urethane bumpers
Is adhesion promoter required before primer on urethane bumpers that are stripped naked ? My bumpers are nearly ready but I will not be spraying anything for a few weeks. Still have doors and rockers to sand. Just getting my supplies together.
Drifting
Joined: Jan 2006
Posts: 1,944
Likes: 22
From: Yooperville MI
Yes, you should use either an adhesion promoter or a special primer for flexible bumpers such as Transtar Waterborne Flexible Primer. This primer fills good, is sandable and performs very good, it eliminates the need for adhesion promoter. Your top coats are applied directly to the primer.
Adhesion promoters are an excellent product but you need to know the exact type of plastic you have for compatibility, because there are different promoters for different plastics. On the back of every part is a symbol to identify the plastic. C4 bumpers are PUR or RIM which is a thermoset polyurethane, so if you go this route you would need a adhesion promoter compatible with PUR or RIM. A lot of promoters are designed for the thermoplastic used on late model bumpers which is different than original C4's and older cars. FYI, thermoset plastics are not repairable with heat like thermoplastic is, if you try to do repairs or plastic welding.
Adhesion promoters are an excellent product but you need to know the exact type of plastic you have for compatibility, because there are different promoters for different plastics. On the back of every part is a symbol to identify the plastic. C4 bumpers are PUR or RIM which is a thermoset polyurethane, so if you go this route you would need a adhesion promoter compatible with PUR or RIM. A lot of promoters are designed for the thermoplastic used on late model bumpers which is different than original C4's and older cars. FYI, thermoset plastics are not repairable with heat like thermoplastic is, if you try to do repairs or plastic welding.
Drifting
Joined: Jan 2006
Posts: 1,944
Likes: 22
From: Yooperville MI
If you have urethane bumpers and you remove all of the paint, you need to use a primer or adhesion promoter designed for refinishing bare urethane, otherwise you risk cracked and peeling paint when the bumper is flexed. Standard body refinishing processes do not apply to urethane bumpers.
Safety Car
Joined: Jan 2009
Posts: 3,704
Likes: 2
If you have urethane bumpers and you remove all of the paint, you need to use a primer or adhesion promoter designed for refinishing bare urethane, otherwise you risk cracked and peeling paint when the bumper is flexed. Standard body refinishing processes do not apply to urethane bumpers.
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
I was on the SPI board, and I believe their Epoxy will adhere fine to the Urethane.
Infact, some of those guys only use Epoxy on Vettes, after that it is just Base/Clear or SS.
The bumpers on my 89 will be easy to strip as whatever they used when they repainted it didn't adhere well. As I bumped the rear bumper, and the paint chiped in big pieces. I'll probably be able to strip the rear bumper just by chipping all the paint off with my fingers.
Infact, some of those guys only use Epoxy on Vettes, after that it is just Base/Clear or SS.
The bumpers on my 89 will be easy to strip as whatever they used when they repainted it didn't adhere well. As I bumped the rear bumper, and the paint chiped in big pieces. I'll probably be able to strip the rear bumper just by chipping all the paint off with my fingers.
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Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
Do you think there would be a problem if the adhesion promoter got overspray on the SMC parts?
And what brand are you using?
Thread Starter
Race Director
Joined: Sep 2003
Posts: 16,838
Likes: 341
From: Database Error Indiana
i think I bought Bulldog AP. My bumpers are off. I am doing a color change. Everyting is off. Easy enough to mask the body off when spraying the APthough .
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
And I guess you pulled the hatch too? I'm trying to figure out the best way to paint around it with the hatch on. I'll be replacing the hatch weatherstripping, so I probably could pull the old off, and tape it up so I don't get paint inside. That would prevent a tape line.
