Rick's Free Auto Repair Advice

Paint plastic bumper

Tips for painting a plastic bumper cover

Painting a plastic bumper cover is completely different than painting a metal surface. And repairing a cracked bumper cover requires completely different repair methods. This article walks you through those difference and shows you how to get the best rusts when repairing a bumper.

Repairing cracks in a plastic bumper

Repairing cracks in a plastic bumper is a two-part process.

Astro Hot Staple Gun 7600

Astro Hot Staple Gun 7600 Kit

First, you have to stitch the crack together to prevent it from separating. The best way to do this is to remove the bumper cover and work from behind using a hot staple tool like the Astro 7600 Hot Staple Gun Kit for Plastic Repair Kit on Amazon for about $90. It comes with the heating gun and an assortment of stitching staples. See this video below for usage.
Avoid these youtube “crack fixes.” They’ll fail early and ruin your repair.

Many youtube bumper repair videos show a crack repair technique where they apply fiberlass drywall tap to the crack and then apply a coating of Bondo filler. This method is guaranteed to fail. First, the self adhesive fiberglass tape is not designed to stick to the types of plastics used in bumper covers, so right off the bat you’ll have a tape failure.

Never use Bondo to fill cracks in a plastic bumper cover

Next, Bondo is never a proper filler for a bumper cover because it’s not flexible. Why would anybody apply a rigid filler material to a flexible plastic bumper? The instant the bumper flexes, even during the installation, the bondo will crack and break off.

Bumper cracks must be filled the with the same type of plastic used in the bumper. So you’ll need a plastic welding tool. plastic welding kit like the Polyvance 5700HT Mini Weld Model 7 Airless Plastic Welder. The kit comes with all the types of bumper cover plastics commonly used by car makers
6027 HT Standard Welding Tip
6031 Tear Drop Airless Welding Tip
200 Watt Ceramic Core Heating Element
2045W Reinforcing Mesh
6124WB Stainless Wire Brush
Starter Pack (15 ft) of round Polyurethane Welding Rod
Starter Pack (15 ft) of round Polypropylene Welding Rod
Starter Pack (15 ft) of round ABS Welding Rod
Starter Pack (15 ft) of round LDPE Welding Rod
Starter Pack (15 ft) of round TPO Welding Rod
Starter Pack (15 ft) of round Nylon Welding Rod
Starter Pack (4 ft) of round Polycarbonate Welding Rod
Starter Pack (15 ft) of flat FiberFlex Universal Welding Rod

Watch the video to see how plastic filling is done.

Next, comes sanding

Your filled crack has to be sanded smooth to get the best finish. What’s the biggest mistake here? Using a dual-action random orbital sander. Most DIYers just go to town on the plastic. They press too hard and go to fast. Then they wonder why they’ve melted the plastic.

Sanding a plastic bumper is a hand-only job

Sand down your filler using a sanding block; no power tools allowed. Hand sanding prevents melting and actually saves you time over DA sanding.

Next comes paint adhesion promoter

If you’re fixing an existing bumper and sanded off the factory paint and primer, you’ll have to apply fresh adhesion promoter to the bare plastic before priming and painting. Skip this step and your primer and paint will just crack off and destroy all your hard work.

Know the type of plastic used in your bumper cover.

bumper plastics
A.B.S. (Acrylonitrile Butadiene Styrene) spoilers, grilles, hubcaps, dashboard interiors, etc.
ABS PC (ABS Polycarbonate Alpha) grids, spoilers, corner protectors, etc.
PA (Polyamide) grids, hubcaps, interior lining.
PC (Polycarbonates) spoilers and corner protectors, grilles, bumpers, etc.
PE (Polyethylene) ducts, batteries, wheel arch liners, bumpers, etc.
PP (Polypropylene) ducts, batteries, wheel arch liners, bumpers, etc.
PP – EPDM (Ethylene Propylene Diene Monomer) bumpers, interior or exterior coatings, spoilers and flaps, etc.
PUR — Polyurethane
PVC (Polyvinyl Chloride) electrical cables, bus floors, etc.
GU-P / BMC-SMC-MMC (Glass Reinforced Polyester Resins) gates, hoods, grids, isotherms, channelling, etc.
GFRP (Glass Fibre Reinforced Plastics) bumpers

Purchase plastic adhesion promoter based on the type of plastic used in the bumper cover. Locate an auto parts store with a custom mix paint department. Purchase plastic adhesion promoter,  along with primer and paint treated with a flex additive to prevent paint crack-off.

If you’re installing a new bumper cover, check with the supplier to see if the bumper has already been treated with a plastic adhesion promoter.

©, 2023 Rick Muscoplat

Posted on by Rick Muscoplat

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