That plastic filler repair on a bumper just peeled off after 3 months

I did a repair on a 2018 Civic front bumper in my shop in Tulsa back in June, used a reputable brand of filler and followed the prep steps. Customer came back yesterday and the filler was lifting at the edges, showing bare plastic underneath. Did I miss something with the adhesion promoter or is this a common issue with certain bumper plastics?

3 comments

3 Comments

the_mary20d ago

Adhesion promoter is definitely key but a lot of people skip the step where you gotta sand the plastic with 80 grit first to really give it some teeth. The newer bumpers on Hondas have that slick coating from the mold that's almost like a release agent, it doesn't matter how good your prep is if you don't break that surface down enough. Also check if you used a flexible filler made for plastics, some of the regular body fillers will just pop off on bumpers because they can't move with the flex. Could be the plastic type too, the PP and TPO bumpers need that specific adhesion promoter that's made for them, not just the basic 2k stuff.

rowanw9120d ago

I get what you're saying about the 80 grit but I've had better luck just using a maroon scotchbrite pad and a ton of cleaner. Going that aggressive with sandpaper on thin plastic bumpers can actually warp them or make the texture show through on the other side if you're not careful. I think it really comes down to the cleaner step more than the abrasiveness if you're using the right promoter.

the_faith20d agoTop Commenter

Oh wow, I totally used to think you had to go heavy on the sanding (like 80 grit was the only way) to get anything to stick to plastic bumpers. But @rowanw91 you actually made me rethink that, especially the part about thinner bumpers warping. I've definitely seen that wavy texture show through on the backside of cheap aftermarket bumpers before, never connected it to being too aggressive with paper. I think you're right that the cleaner step gets overlooked way too much, like if you're not getting all that mold release off first nothing is gonna bond anyway. I've been using a grey scotchbrite and a strong wax and grease remover lately and it's been holding up just as good as when I was sanding the hell out of them. Appreciate you changing my mind on this one, saved me some headaches.