Plastic, Fibreglass and Composite Panel Repair
Plastic, Fibreglass and Composite Panel Repair
This domain tests identification of plastics and composites, repair method selection and adhesion. Exam questions often ask whether a part can be welded, bonded or must be replaced.
Core rules
- Thermoplastics soften with heat and can often be plastic-welded; thermosets cure permanently and cannot be welded. Check the part identification or conduct a test.
- Polypropylene and some bumper plastics have low surface energy; they need a dedicated adhesion promoter or plastic welding with a compatible rod.
- Clean and bevel cracks, stop-drill the ends and use backing where access allows. Weld or bond with the specified product.
- Fibreglass repair uses polyester or epoxy resin with chopped strand mat or cloth. Grind a taper, laminate in layers, and finish with gelcoat or primer.
- Flexible parts need flexible filler and flex additive in the paint system.
- Follow cure times and do not apply paint over uncured resin or adhesive.
Worked example
A cracked PP/EPDM bumper cover is flexible and has a torn mounting tab. Reasoning: identify the plastic, clean both sides, stop-drill the crack, groove it, plastic-weld with compatible rod, and reinforce the tab with a mesh or backing. Use flexible filler and an adhesion promoter before paint. A rigid epoxy without promoter may peel.
Traps
Welding a thermoset; using the wrong rod; painting over release agent; no stop-drill; rigid filler on a flexible bumper.
Key points
Thermoplastics can be welded; thermosets cannot. Polypropylene often needs an adhesion promoter. Stop-drill cracks and bevel before welding. Fibreglass repairs need a tapered laminate and compatible resin. Flexible bumpers need flexible filler and paint additives.