Plastic Bumper Repair Welding NZ | Fix Cracked Bumpers Properly

Q: How long does a typical bumper repair take?

A standard crack repair takes 15-25 minutes of welding plus paint prep time. A more complex repair can take 45-60 minutes.

Q: Is the repair as strong as a new bumper?

A properly welded repair recovers around 80-95% of the original tensile strength of the bumper plastic.

Q: Can I weld a painted bumper?

Strip back about 10mm either side of the crack before welding, then refinish after.

Q: What rod colour for an unpainted black bumper underside?

Black PEMD rod. For visible painted repairs colour doesn't matter under the paint.

Q: Will welding work on a polypropylene bumper?

Yes, but you need PP rod and a slightly higher welding temperature (around 320C versus 280-300C for PEMD).

Plastic Welding Tools NZ Ltd, supply a complete range of plastic welding supplies –

Including: plastic welding tools, plastic welding kits, accessory nozzles, plastic welding rods, spare parts and information on how to weld plastics according to worldwide DVS joining standards.

Our equipment is designed for commercial users – reliable, innovative, and precision engineered for the toughest plastic welding fabrication and repair work.

Manufactured in Switzerland, Austria & Germany. We also provide service & backup covering all major brands – including: Techspan Plastic Welding tools, BAK, Dohle, Herz, and Leister.

Videos – How to Weld & Repair Plastic

See our short video clip – Plastic Bumper Repair Welding Demo

See our full Instructional Welding Video – How to Weld Plastic

Need more information?

How automotive plastic bumper repair welding works

Almost every car bumper made in the last 20 years is moulded from PEMD (medium-density polyethylene). When the bumper cracks, splits or breaks a tab, the polymer can be hot-air welded back together using matched PEMD welding rod. The repair is structural – a properly welded bumper recovers most of its original impact strength.

The basic process is:

Confirm the plastic. Modern bumpers are stamped on the inside with the recycling code or polymer marking (most commonly “PE” or “>PE-MD<"). If unmarked, the burn test or a quick check with a hot welder will confirm.
V-groove the crack on both sides with a sharp blade or rotary cutter. The V-groove gives the rod somewhere to fuse into.
Tack the crack closed at intervals using a tacking nozzle so the bumper doesn’t shift during welding.
Run the speed nozzle along the V-groove with matched PEMD rod, fusing the rod into the substrate as you go.
Reverse and weld the back side of the crack for full-thickness fusion.
Cool, then sand back the weld bead flush with the bumper face.
Paint prep (sand, fill any pinholes, prime, paint) if the repair is on a visible panel.

What you need

A hot-air welder, typically Techspan Rion or Triac
4mm round PEMD welding rod, colour-matched if doing visible repair (we stock natural, black, grey, beige and several other automotive colours – see PEMD welding rod)
A speed nozzle to feed the rod into the weld
A tacking nozzle for initial crack closure
Speeds up significantly if you have an automotive plastic welding kit with all the consumables pre-matched

FAQs

How long does a typical bumper repair take?

A standard crack repair takes 15-25 minutes of welding plus paint prep time. A more complex repair with multiple cracks or a torn tab can take 45-60 minutes. Compared to ordering a replacement bumper from a wrecker or dealer, the cost saving is typically 60-80%.

Is the repair as strong as a new bumper?

A properly welded repair recovers around 80-95% of the original tensile strength of the bumper plastic. For most bumper applications, this is well within the safety margin of the part. The weld zone is often stronger than the surrounding plastic if rod and technique are correct.

Can I weld a painted bumper?

You need to remove the paint from the weld zone before welding – the paint will scorch and contaminate the weld. Strip back about 10mm either side of the crack with a flap disc or sandpaper, weld, then refinish.

What rod colour for an unpainted black bumper underside?

Black PEMD rod. For visible painted repairs, colour doesn’t matter under the paint, so natural rod is fine. For exposed surfaces (trims, underside, splash guards) match the rod colour to the bumper.

Will welding work on a polypropylene bumper?

Yes, but you need PP rod, not PEMD – the rod must match the substrate polymer. PP runs at a higher temperature (around 320C versus 280-300C for PEMD). Check the polymer stamp inside the bumper to confirm.

Related guides

How to identify plastics before welding – polymer ID techniques
Plastic repair of a motorsport bumper – worked example
How strong is plastic welding? – strength data