How to fix a cracked bumper

A cracked plastic bumper can be repaired rather than replaced in most cases, but the repair that lasts is a plastic weld from behind, a flexible filler and primer on the front, and a colour-matched respray. The DIY kits from the auto shop do part of that job. They rarely hold up on a bumper that flexes every time you close the boot or hit a speed bump.

What's actually cracked

Bumpers are flexible plastic, usually polypropylene, over a metal or foam reinforcement. A crack means the plastic has split. If the mounting tabs or clips are broken too, the bumper won't sit straight no matter how well the crack is fixed, and that's when a replacement is the better call. Check: is the bumper still sitting flush with the guards? If it's sagging or there's a gap, something behind it is broken.

The DIY option

Epoxy kits and plastic repair kits bond the crack from behind and fill it from the front. Done carefully on a small crack away from the edges, they can hold. The problems:

• The repair is stiffer than the plastic around it, so it cracks again at the edges of the patch.
• Most kits don't include a plastic adhesion promoter, so paint and filler peel off.
• The front still needs colour. A spray can never matches, and the result shouts "repaired".
• Getting the bumper off to work from behind is half the job, and most people try to fix it on the car.

If the car's old and the look doesn't matter, go for it. If it's a car you care about, read on.

How a panel shop fixes it

1. Off the car. Lights, sensors and trim removed so we can see every tab and work from behind.
2. Identify the plastic. There's a code moulded inside (PP, PP/EPDM, ABS). The repair rod has to match.
3. V-groove the crack on the back and plastic-weld it with a matching rod, often with a mesh reinforcement melted in. This restores the plastic's flexibility rather than fighting it.
4. Front side: grind the crack, flexible filler, sand smooth.
5. Adhesion promoter and flexible primer, guide coat, block sand.
6. Colour-match from the paint code with a test card against the car, then colour and clear in the booth, with flex additive where the paint calls for it. Blend into the guard if the damage runs to the edge.
7. Refit, align the gaps, test the parking sensors.

Our page on how plastic bumper repair works goes into each step.

Repair or replace?

• Repair: one or two cracks, tabs intact, bumper still sitting straight.
• Replace: broken tabs, multiple tears, distorted shape, or a cheap bumper where a new one costs less than the labour to fix the old one.

We'll quote both if it's borderline. See bumper repairs and what sets a bumper repair price.

How long

Two to three days for a crack repair and respray. A replacement depends on getting the part.

Insurance?

A cracked bumper from a car-park bump often lands near your excess, so many people pay privately. Bigger damage, or someone else at fault, usually means a claim. Our insurance versus private guide covers it.

Send a photo of the crack and one of the whole bumper through the quote form and we'll tell you what it needs. H&H Smash Repairs, 77 Moss St, Slacks Creek.