Wrench Tip: How to Fix a Bumper Cover

Wrench Tip: How to Fix a Bumper Cover

by David Zipf

Fender benders suck.  Even a light knock can craze paint, crack light lenses, and put holes in bumpers.  While the damage usually isn’t structural, replacing all those plastic bits can be a real hassle and it gets expensive fast.  And then there’s paint: not only do you lose your car for a time, but a respray is never quite as good as the factory paint.  Surely, if you have been in a minor parking lot scuffle, there’s a better way of dealing with plastic damage than to chuck the bumper and start from scratch?  Luckily enough, there is.

 

The donor car for this experiment is a 2008 Mazdaspeed 3.  The car has never been in a reported accident but, as you can plainly see, something has happened to the front end of this car.  There are no signs of impact on the bumper: no scuffs, no crazed paint, and no broken bolts underneath where the belly pan meets the bumper cover.  However, all of the mounting holes on the sides of the bumper are split.  My guess?  The previous owner of this car curbed the lower lip and ripped out the bumper while backing off.
Job one is to get the bumper off.  In the 3, it’s fairly easy: remove some clips along the fender liner, remove a few more under the hood, remove a dozen bolts along the bottom, and unplug the fog lights and external temp sensor.  Because of the unique nature of this bumper’s damage (all of the damage is to the mounting points which are hidden by other bodywork when the bumper is reinstalled), we should not have to repaint it, so we did all of our work on this big plastic tarp to prevent scratching the paint.  Not having to repaint the bumper will save us a ton of time and money.
With the bumper off, we can get a better idea of what needs fixing.  This should be a bolt hole, but as you can see, it has been ripped off.  Some of the old plastic was trapped under the bolt head, so we salvaged it.  We can use it as a template or potentially bond it all back together.
These holes are for plastic clips and hold the fender liner to the bumper.  The direction of the splits lends credence to the idea that the bumper got caught on something and was pulled off.  Because of the split hole, the retaining clip has nothing to grab to.  If we can repair the split and rebuild the missing holes, we can salvage this bumper, thus saving a trip to the body shop or eBay.
This is all you need to repair your bumper.  We used Bondo’s bumper repair kit.  It includes a tube of two-part repair adhesive, a spreader, and a plastic mesh used to give some structure to the parts being glued back together.  You will also need sanding tools and something to mix the adhesive on.  If you are repairing areas that are exposed, you will also want some of this special teflon coated plastic which will allow you to smooth and shape the adhesive before it sets, saving time and resin.  Since all of our repairs aren’t going to be visible, we didn’t bother.  The Bondo kit is relatively expensive for the amount of epoxy you receive.  If you have a lot of repairs to do, it’s best to buy the adhesive in bulk.  You could use JB Weld for this if you’re REALLY cheap, but be warned: JB Weld is very runny before it sets and will get everywhere.  The 3M/Bondo expoy will bond better and is more flexible than JB Weld, so the repairs will be less likely to fail again.  The resins in the 3M product have a similar thermal expansion rate to plastic, so it won’t fail due to the bumper growing or shrinking more than the repaired area.  Some of these epoxies also have carbon fibers embedded into them which make the repairs stronger still.  All in, we spent no more than $50 on two repair kits, a pack of multi-grain sandpaper, and a foam rubber sanding block.  You will also need a bucket (or Chinese takeout tub) of water for wet sanding and a hand drill.  $50 isn’t bad when you consider a used bumper would cost over $200 (provided we we able to find one in our car’s color) and a new, painted one would be even higher.

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