Painting a plastic bumper

Anything goes in the world of fiberglass and plastic



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PostPosted: Tue Mar 05, 2019 12:08 pm
Hi All
I've got a plastic bumper from a BMW (1999 model).
Its got the factory clear/base paint on it. I've had to do a repair as it was cracked all the way down the one side. I used a hot stapler gun and melted the stitch staples in from the rear. Then I ground a groove all the way down the cracks. Then carefully sliced some slivers of plastic from underneath the bumper from the part which is covered by the undertray, and proceeded to melt these into the grooves using the hot gun. I also used a special epoxy with a mesh from the rear (product sold for this purpose) for further reinforcement. Then filled all the recesses with a UPOL plastic bumper filler. Repair seems very solid.

My first question is:
I'm wanting to avoid any chance of adhesion problems. I have half a tin of KAPCI 615 Adplast Primer - https://www.flpgroup.co.uk/data-sheets/FLK615-TDS.pdf

I've used this before on a brand new bumper which was uncoated. And it worked great. But this bumper is used, with factory paint. It doesn't say anything on the data sheet about compatibility with existing coatings, and seems to be made for fresh plastic. Has anyone used an adhesion promoter before and coated 240grit scuffed factory paint before? Should I just mist some on the repaired area or cover the whole bumper? What you think?

thanks

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PostPosted: Tue Mar 05, 2019 11:58 pm
Everything I could pull on different P. sheets and data sheets keeps emphasizing that this primer is supposed to go on bare plastic. Having said that I would like to point out that one of the "plastics" that are listed on there is polyurethane soooo.... that existing clear is probably a factory urethane. I doubt that you would get into trouble using however it seems like using a dedicated urethane or epoxy sealer would be a better route to go...... I generally only use adhesion promoters on bare plastics. I treat an already painted bumper just like any other surface I would paint over....sand it up good for bite and then seal.
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PostPosted: Wed Mar 06, 2019 2:01 am
DarrelK wrote:Everything I could pull on different P. sheets and data sheets keeps emphasizing that this primer is supposed to go on bare plastic. Having said that I would like to point out that one of the "plastics" that are listed on there is polyurethane soooo.... that existing clear is probably a factory urethane. I doubt that you would get into trouble using however it seems like using a dedicated urethane or epoxy sealer would be a better route to go...... I generally only use adhesion promoters on bare plastics. I treat an already painted bumper just like any other surface I would paint over....sand it up good for bite and then seal.


Thanks for this. Yes, that's some good logic about the urethane compatibility. I think I'll mist some of this stuff on the repaired areas which have exposed the bare plastic and see how it goes.

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