How a plastic bumper is repaired, step by step

Most bumpers on cars built in the last thirty years are plastic, and plastic repairs well if you treat it as plastic rather than metal. Dents are reshaped with heat, cracks are welded or bonded, and the paint goes on over a flexible primer so it bends with the bumper instead of cracking. Here's what happens to your bumper at Moss St.

1. Off the car

The bumper comes off. Trying to repair it on the car means working around lights, sensors and the panel edges, and you can't get behind a crack. Off the car we can see every clip and tab, and we check the mounting points, the reinforcement bar behind it and the absorber foam. Broken tabs are the thing that turns a repair into a replacement, so this is the first decision.

2. Clean

Road grime, wax and old polish stop primer sticking. The bumper is washed, degreased and, around the repair, scuffed back to raw plastic.

3. Reshape dents with heat

Plastic has a memory. A pushed-in corner can often be warmed with a heat gun from behind and eased back to shape, then cooled so it holds. No filler needed for a clean dent.

4. Repair cracks

Cracks are V-grooved along their length, the plastic is identified (there's usually a code moulded inside, like PP or PP/EPDM) and a matching rod is plastic-welded into the groove from behind, sometimes with a mesh reinforcement. Alternatively a two-part adhesive is used on the back for smaller cracks. The front is then ground flush and filled with a flexible filler.

5. Deep scuffs and gouges

A gouge is sanded back to sound plastic, filled with a flexible filler, and sanded smooth. Scuffs that haven't removed material are just sanded and feathered into the surrounding paint.

6. Flexible primer

This is the step that separates a bumper repair from a panel repair. Plastic flexes; ordinary primer doesn't. A plastic adhesion promoter goes on first, then a flexible primer, then it's guide-coated and block-sanded until the surface is dead flat.

7. Colour match and paint

The colour is mixed from the car's paint code and tested on a spray-out card against the car. Then colour and clear are sprayed in the booth, with a flex additive where the paint system calls for it, and baked. We blend into the adjoining panel if the damage runs to the edge. More on colour matching.

8. Refit and check

Sensors, cameras, fog lights, grilles and trim go back on. Parking sensors are tested. The bumper is aligned so the gaps to the guards and bonnet match, then the car is washed and inspected.

Repair or replace?

Repair when it's scuffs, scratches, a dent or a crack or two with the tabs intact. Replace when tabs are gone, the plastic is torn in several places, or the bumper is distorted. We'll quote both if it's borderline. See bumper and scratch repairs and our note on bumper repair costs.

Will the repair last?

A properly welded and primed plastic repair lasts as long as the bumper. The failures you see on cheap repairs (paint flaking off the corner, a crack reappearing) come from skipping the adhesion promoter, using rigid filler, or painting over a crack that was never welded.

Got a bumper that's copped it? Send a photo and we'll tell you what it needs.