Repairing a cracked plastic bumper

The bumper takes more punishment than any other part of the car: kerbs, tight parking spaces, a low-speed nudge in traffic. Because it is plastic, it often does not dent; it cracks. And the question comes straight away: does it need replacing, or can it be repaired?

It depends on the damage, but in many cases a crack or a small missing piece can be repaired with a good result, saving the cost of a new part and painting it in full. It has to be done methodically, though, because badly repaired plastic splits again with vibration and changes in temperature.

When repairing makes sense

• Cracks of moderate length on flat or gently curved areas.
• Small missing sections or broken corners that can be rebuilt.
• Distortions that the plastic will allow to be corrected with heat.
• Broken tabs or mounting points that can be reinforced.

When the bumper is badly shattered, large pieces are missing or the sensor brackets and mountings are destroyed, replacement is usually the better option. We will tell you clearly in the quote.

Preparing a crack

The first step is to line up both edges of the crack so that the surface is continuous once it is closed. Then a small hole is drilled right at the end of the crack. It sounds like a minor detail, but it matters: the hole spreads the stress and stops the crack from travelling further through the plastic, much like a crack in a windscreen.

Next, the crack is bevelled, opened into a V shape on one or both sides depending on the thickness of the plastic. That way the repair material penetrates and grips through the full thickness, rather than just sitting on the surface.

Closing and reinforcing

Depending on the type of plastic and the damage, the crack is closed with plastic welding, with two-part structural adhesive, or a combination of both. A reinforcement such as a mesh or patch is usually added on the inside, giving strength where nobody will see it.

Before any adhesive goes on, the surfaces are thoroughly sanded, cleaned with plastic-safe products and treated with an adhesion promoter. Many automotive plastics are naturally hard to bond and paint; this product ‘activates’ them so that adhesive, filler and paint genuinely stick.

Levelling and painting

With the crack closed and reinforced, a flexible filler designed for plastic is applied, one that moves with the part without cracking. It is sanded, primer surfacer is applied, and the bumper is painted to match the rest of the car. If the part has unpainted textured areas, these are treated too so they look original.

What about parking sensors?

Many bumpers carry sensors or brackets for them. During the repair they are removed carefully and refitted in exactly the same place, with attention to the paint thickness in that area so their operation is not affected. If a bracket is broken, we assess whether to repair or replace it.

If your bumper has a crack, a scrape or a broken corner, have a look at our bumpers and plastics service or ask for a quote. We will tell you whether it is worth repairing or whether replacement makes more sense.