Wrench Tip: How to Fix a Bumper Cover


With tools in hand, the first job is to sand back the paint.  Give yourself a wide area to work in, so sand back a lot of paint.  You also want to rough up the plastic to get a better bond, so use a rough grit.  We alternated between 320 and 180 grit.  For large areas, you will want to use a power sander, but for these tight areas, hand sanding is preferred.
Next, break out the drill and a small bit.  You will be drilling a series of holes around your repair.  This sounds crazy, but there’s a reason for it.  If you simply slather on the adhesive, your repair is only strong in two directions (along the face of the plastic itself).  By drilling some holes, you now have to shear the epoxy in all three planes.  You’re taking advantage of the mechanical properties of the epoxy, not just the chemical bond to the plastic.  The epoxy will always bond better to itself than the plastic bumper, so this is a crucial step.  It is also wise to sand in a V-shaped groove into any splits for the same reason.  We had 8 of these damn things to fix in a single day, so we kind of skipped that step.  Time will tell how wise that was.  Once you’re done drilling, sand off the flash and clean the surface.  We used some denatured alcohol to clean off any leftover dirt and grease.
Next, cut out a piece of mesh to cover the damaged area.  On complex areas like this, it’s best to tack it in place with a small amount of resin first so it doesn’t move around too much before you completely fill the damaged area.
Once the epoxy has partially set (10-15 minutes depending on temperature and humidity), mix up a big batch of goo and slather it on.  Go ahead and cover up the hole: it can easily be re-drilled once you’re done (obviously make sure you know where it’s located!).  We will also trim off the extra mesh and any extraneous plastic once it’s all cured.  The dried epoxy can be shaped, creating a seamless repair in exposed areas.
For the passenger side bolt hole, we were able to find all of the original pieces.  We were able to use them to rebuild this corner completely.  Note the rubber gloves.  This epoxy is very sticky and if it gets on your hands, it will get everywhere.  Pro cleaning tip, if you use a rag and denatured alcohol when the resin is still wet, it comes off relatively cleanly.
On the driver’s side?  No such luck.  With most of the original plastic missing completely, we had to get creative.  We picked up an extra body filler spreader and sliced off part of the end to use as a replacement.  This plastic is very flexible, so it is less likely to crack once repaired.  It also comes pre-tapered, which makes it a lot easier to fit it into a tight area.  It’s important we don’t make these too thick, or the body lines won’t line up correctly.  We also had to sand the bumper to a taper to give us a nice, strong lap joint.  Using the broken pieces of the opposite side, we traced and trimmed the bit of spreader to nearly the correct shape (but we did not photograph the trimmed down part).
The vertical holes were badly split and needed some pressure to keep them from spreading as the epoxy dried.  Holding the thing together by hand for 15 minutes while the epoxy set wan’t going to fly.  A bungee and 4-lb sledge hammer are very useful here, applying just enough pressure to hold everything together, but not enough to deform the bumper and misalign the split seams.

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