How to fix a plastic car bumper

Tools and Materials

• Sandpaper (in varying grits)
• Plastic bumper repair kit
• Adhesion promoter
• Primer
• Paint matching your car's colour
• Clear coat
• Heat gun or hairdryer (for more advanced repairs)

Note: When dealing with plastic repairs on vehicles, always stick to the instructions on filler, adhesion promoter, primer, and paint as they can vary between similar products.

Assess the Damage

Before diving into repairs, it's essential to assess the extent of the damage to your plastic bumper. Determine whether it's a minor scratch, a crack, or a more significant structural issue. This will help you choose the most appropriate repair method and ensure a successful outcome. If not painting the entire bumper, you will need to blend the repair into the existing paintwork.

Minor Scratches

With any minor scratches try a scratch remover car care product first. This will clean up the area and give you an idea of what you have left to fix. Sometimes touch up paint is all you need. You can apply this, let it dry thoroughly and then cut and polish it. If it is too big or severe for touch up paint to cover then you need some or all of the steps in the Major Scratch repair section below. It may need sanding, priming, and painting or filling, sanding, priming and painting.

If sanding is required start with fine grit paper like 600 grit wet and dry. If the scratch is still there try 320 grit. If 320 grit won’t remove it, filling is required. Remember to keep the sanding to the repair area and make sure the bumper is not dented and that the scratch is the only problem.

Major Scratch

This is where you may have scraped something like brick wall that has torn off paint down to the plastic. It can sometimes cover a large surface area. It is mainly cosmetic, and the shape of the bumper has not been compromised. It is also usually on a corner of the bumper, so you are not required to paint the entire bumper bar.

Different Paints

When assessing, take into account how the painting will work. Use a panel edge or a body line when you finish the painting, if possible, as the repair will be less obvious. Each paint process should overlap when blending. Primer should overlap the repair area, paint colour should overlap the primer area, and the clear coat should overlap the paint colour area.

The article covers modern base coat, clear coat paints. For older vehicles using a gloss enamel use the Preparing for Colour and Spraying Paint Colour sections. No need to do the Clear Coat sections. The only part you need to change is to extend the paint area to cover what you would have done in Clear Coating. This step is where you blend the repaired area into the existing paint finish. 

Prepare the Surface

Start by thoroughly cleaning the damaged area of the bumper with soap and water to remove any dirt, grease, or debris. Then, use a 180-grit sandpaper with a sanding block to roughen the surface around the damaged area. This helps the repair materials adhere better and ensures a smooth finish. Focus mainly on the scratches to remove as much damage as possible. Do not sand it too heavily as you do not want to thin out the plastic, you simply want to smooth it down and remove any pieces of sticking out paint or plastic.

Next use some 320-grit sandpaper with a sanding block to feather the edges so it blends into the panel. This is where you widen the repair area to encompass some of the painted undamaged panel. Use isopropyl alcohol or a wax and grease remover to clean the bumper.

Using Filler

Use an adhesion promoter and flexible filler that is designed for plastic bumpers. First spray on a light coat of adhesion promoter which helps the filler stick to the plastic. When dry use the filler. The filler will involve mixing it with a hardener and then applying with a with an applicator. It is one of those jobs where practise makes perfect. Ideally start with just skim coats or light coats of filler, don't put it on too thick as that will cause you more sanding work. Follow the contours on the bumper with the filler.

Wait until it hardens before sanding. If the filler is fairly thick or uneven and it needs a lot of sanding, you can use a courser grit of sandpaper like 80 grit and a sanding block. Just use it on the filler and not the surrounding paintwork as it will scratch it too deeply. Then go back to 180 grit and a sanding block as it flattens out. Chances are that you'll need to add more filler after your first sanding. This may be to pick up small imperfections or areas that you missed. Ideally you want to get the filler stage as smooth an accurate as you can before painting.             

Before priming, work out the area you want to spray and if it hasn’t been sanded use a Wet & Dry 600 grit sandpaper and a soft block or a Scotch-Brite pad to scuff it up. The area you prime should always be smaller the area you paint colour on. Use isopropyl alcohol or a wax and grease remover to clean the bumper.

Using Primer

Good masking is vital for a professional finish. Mask the area you want to prime. Don’t forget to cover things like wheels and tyres. On panel joins it will be a hard edge, were on open areas, roll the paper over so it allows some of the primer to over spray underneath it. This will give it a soft feathered edge while containing the primer. Ideally you want to limit the primer to the repair area itself.

Use an adhesion promoter and plastic primer which is designed to be flexible. First spray on a light coat of adhesion promoter which helps the primer stick to the plastic. Once dry you can now prime the repair. For small repairs like this you can use a spray gun connected to a compressor or you can use a rattle can. Either method will work successfully. Use light even coats allowing it to dry between coats.
Three coats of primer should do the trick. If you can still see the repair through the primer, give it another coat.

Preparing for Colour

Once primed and the primer has dried, use wet and dry 600 grit sandpaper with a soft block to rub it back. Check for any imperfections. Once ironed out and sanded, it is time to remask for colour. Expand the area to allow the paint colour to cover the primer. If you masked on a panel join, leave it as it is provided there is enough gap for the colour to wrap around the bumper edge. If not, you may need to remask slightly, so the paint colour covers the primer. Use isopropyl alcohol or a wax and grease remover to clean the bumper.

Spraying Paint Colour (Base Coat)

The important thing here is making sure you get the correct colour match for your vehicle. On older vehicles this is straightforward as there will be a data plate or sticker with the paint code on it. If not you may need to check the owner’s manual, Google it or contact the paint supplier armed with your vehicle details. Buy the clear coat to match the colour at the same time.

Just be aware that the paint you order will be the colour the car was painted at the factory. Your vehicle maybe rather sun faded, so this colour will look different when sprayed on your vehicle. If this is the case, you can get the paint mixed so it more resembles how the paint is on your vehicle today or you may choose to paint the entire bumper for colour uniformity.

Once you have the colour in either a tin or rattle can, applying it is the same for both. Just use even light coats allowing drying time between them. The colour will not dry with the same gloss finish as the remaining panel work and should overlap the repair and primer. 

Preparing for Clear Coat

Once the colour has dried, remask again to expand the area so it overlaps the colour. This is the final mask, and the same rule applies to panel edges. You can use 1000 grit wet and dry sandpaper or equivalent Scotch-Brite pad to smooth out any rough spots in the colour coat and to scuff newly exposed panels from the remasking. Use isopropyl alcohol or a wax and grease remover to clean the bumper.

Spraying The Clear Coat

Use a tack rag to give the area a quick wipe down to get rid of any dust and dirt that has fallen onto the panel before spraying. Start with a light coat of clear and when dried you can use a heavier second coat, so it is wetter and overlaps the first coat. Once dry, carefully remove the masking.  

Buff and Polish

After the clear coat has fully dried, use a buffing compound and a polishing pad to buff the repaired area to a smooth and shiny finish. This helps blend the repaired section seamlessly with the rest of the bumper and gives it a professional appearance.

Holes, Cracks & Dents

This is when the bumper has been knocked out of shape and it is not just fixing a simple scratch. You need to actually fix the shape of the bumper as well as the scratches. If the bumper is this bad, removing it from the car maybe your best option as you may need to get in behind it to fix some of the problems.

This is when a heat gun can come in handy to push out dents and reshape the bumper. You can use panel beating dollies to help shape the bumper. There are also plastic adhesives you can use to fix cracks or tears in the plastic. Another option is plastic welding.

Final Touches

Once you're satisfied with the repair, give the entire bumper a thorough cleaning and waxing to protect the finish and maintain its appearance. Step back and admire your handiwork – your plastic bumper is now as good as new!