How to Repair Car Plastic Trim: Scratches and Fading

Plastic makes up a large part of a modern car: bumpers, grilles, mirror caps, sill covers, arch extensions, roof rails and most of what you touch inside. It is light, tough and cheap to mould, but it fades in sunlight, marks easily and cracks when it is cold and something hits it. The good news is that most trim damage is fixable at home, provided you use products designed for plastic rather than products designed for paint.

What causes plastic trim to fade, crack and scratch?

UV light is the main culprit. Sunlight breaks down the surface of the plastic and drives out the oils and pigment that give it colour, leaving the chalky grey layer you see on older bumpers, arch trims and mirror caps.

• UV exposure causes fading, chalking and eventual surface cracking. Cars parked outside all year, and horizontal surfaces such as roof rails and scuttle panels, suffer worst.
• Water and road grime leave staining and, in shaded areas that stay damp, green algae growth along the edges of trim.
• Grit and careless washing scratch the surface. Textured plastic shows scuffing more readily than paint because the raised grain takes the hit.
• Cold weather impacts. Plastic becomes brittle in low temperatures, which is why bumper cracks are far more common in winter car parks than in summer.
• Cleaning products meant for other jobs. Solvent based cleaners, all purpose cleaners used too strong and even some wheel cleaners will bleach or dry out trim.

Interior trim fails differently. Door cards and centre consoles pick up scratches from keys, buckles and shoes, gloss black trim shows every swirl mark, and dashboards go shiny where they catch the sun.

What you need to repair plastic trim

• Plastic safe cleaner and a microfibre cloth, or a mild car shampoo solution and a soft brush for textured surfaces.
• Isopropyl alcohol or panel wipe for the final degrease before any product goes on.
• Fine grit wet and dry sandpaper, typically 600 to 1500 grit, for levelling raised scratches.
• A plastic trim repair compound or filler, for cracks and gouges. It must stay flexible when cured.
• A plastic scraper or spreader to work filler in flush.
• Trim restorer, dressing or dye for faded exterior plastic.
• Plastic polish for gloss surfaces and clear plastic lenses.
• Masking tape to protect the paint next to the trim.
• A hairdryer or heat gun, used carefully and at low heat, to make plastic more flexible before working on it.

Keep car wax and paint polish away from textured plastic. Wax dries white in the grain and is a genuine nuisance to remove, and abrasive paint polish flattens the texture and leaves shiny patches.

How to prepare plastic trim for repair

Preparation decides whether the repair lasts a season or a week, because nothing bonds to a surface carrying old dressing, wax residue or degraded plastic.

1. Clean the trim thoroughly. Use a plastic safe cleaner and a soft detailing brush to get into the texture. Rinse and dry.
2. Strip old products off. Wipe the area with isopropyl alcohol or panel wipe. Silicone based dressings applied over the years leave a film that stops restorer and filler bonding.
3. Mask the surrounding paint. Tape along the edge of the trim so nothing you use spreads onto the panel.
4. Sand any raised or rough areas. Wet sand lightly with fine grit paper. On textured trim, sand only where you have to, since sanding flattens the grain.
5. Warm the plastic if it needs to flex. A hairdryer or heat gun on a low setting makes plastic easier to work with, particularly when refitting a distorted trim or coaxing a shallow dent out. Keep the heat moving and never hold it in one place. Overheated plastic distorts, glosses over or blisters, and none of that comes back.
6. Degrease again before applying filler, dye or paint.

How to repair scratches and cracks in plastic trim

Light scratches sand and polish out. Deeper damage needs filling and levelling before you address the colour.

• Light surface scratches on smooth or gloss plastic. Work through fine grit wet and dry paper, then finish with a plastic polish on a soft cloth until the gloss returns.
• Scratches on textured trim. Sanding removes the grain and makes the repair more obvious. On these, clean thoroughly and use a trim restorer or dye to blend the mark, and only sand if something is standing proud.
• Gouges and cracks. Clean out the damage, warm the area slightly, then work a plastic repair compound in with a spreader and scrape flush with the surrounding surface. Build it up in thin layers rather than one thick one, allowing each to cure.
• Sand the cured filler back with fine grit paper until it is level, feathering the edges into the surrounding plastic.
• Restore the colour. Apply trim restorer, dye or paint depending on the finish, in light coats, feathering out past the repair.

Deep cracks that go through the plastic, and any crack around a mounting point or screw boss, are a different matter. A body shop repairs those by plastic welding, which fuses the material back together from behind and gives a repair that can take load. Filler alone in a structural area will let go the first time the panel flexes.

How to restore faded black plastic trim

Faded trim needs a product that either replaces the lost oils or adds a new coloured layer. Washing achieves nothing because the grey is the degraded plastic itself.

Whichever you use, apply it thinly and evenly with a microfibre applicator, cover the whole panel rather than one patch, and buff off any excess. Half treated trim looks worse than untreated trim.

Polishing plastic trim and gloss black interior

Gloss black interior trim is one of the easiest surfaces on a car to scratch and one of the hardest to keep looking right. It marks with a dry duster, let alone a cloth carrying grit.

• Use a clean plush microfibre cloth and a quick detailer rather than a dry wipe.
• Light swirls in gloss black plastic can be polished out with a fine plastic polish worked by hand or on a small dual action pad, using light pressure.
• Headlight lenses and clear plastic covers use the same approach: sand progressively, polish, then protect. Left untreated they yellow again fairly quickly.
• Textured plastic gets a dressing, not a polish.

How to stop plastic trim fading again

• Wash the car regularly with a mild car shampoo. Strong traffic film removers and jet wash pre sprays strip trim.
• Park in shade or a garage when you can, or use a cover on a car that lives outside.
• Reapply a trim protectant every three to six months, sooner if the water stops beading.
• Keep wax, paint polish and abrasive pads off textured surfaces.
• Wipe bird droppings and sap off promptly, since both stain plastic as readily as paint.
• Use a sunshade to slow dashboard and door top fading inside.

When is trim repair a job for a body shop?

Take it to a body shop when the plastic is cracked through, when mounting tabs have broken, or when the part is painted and the damage has gone past the surface.

• Cracked or split bumpers are welded from behind, filled, primed and refinished. That is normally a far better answer than a new painted bumper, and we do this daily as bumper repairs.
• Scuffed painted trim, mirror caps and sill covers suit a localised SMART repair, blended into the surrounding finish in a few hours.
• Broken mounting tabs can sometimes be welded, but a trim panel that no longer sits flush is often better replaced.
• Faded trim on a car going back at the end of a lease is usually cheaper to sort beforehand than to pay for at inspection.

If you are unsure whether something is a filler job or a welding job, send a couple of photos through our quick quote form. We will tell you if it is worth doing yourself.