Am I the only one who hates using filler putty on aluminum bumpers?

Last week I took a job on a 2020 Ford F-150 with a dented rear aluminum bumper at my shop in Phoenix. The customer wanted a cheap fix, so I grabbed my standard polyester filler, slapped it on, and sanded it smooth. Three days later the bumper came back with cracks all along the filler line. I had to grind it all off and start over with a two-part epoxy filler meant for aluminum. That mistake cost me about 4 hours of rework and $35 in wasted materials. My old timer mentor told me years ago that aluminum flexes different than steel, but I thought he was just being picky. Has anyone else dealt with filler failing on aluminum, or is it just me learning the hard way?

2 comments

2 Comments

kai6577d ago

Nah, that's not quite right - polyester filler works fine on aluminum if you use the right primer first.

gonzalez.grant7d ago

1970s aluminum boats taught me this lesson the hard way. I used a standard polyester filler on an old Starcraft hull without etching the metal first and it peeled right off after a few months. The trick is a two-step wash with a phosphoric acid etch cleaner, then a zinc chromate primer. That primer gives the filler something to bite into. Even with the right prep, I still prefer epoxy fillers for aluminum because they bond better and don't shrink as much over time. But if you have polyester on hand and use the proper primer, it can work for smaller dings and scratches. Just don't skip the etch step or you'll be redoing the job in six months.