BMW April 2022

A significant amount of plastics are used in the vehicle manufacturing process and these areas are particularly prone to damage and can be expensive to replace. However, it is possible for a plastic component to be repaired rather than replaced. Refinishing products are able to provide an easy to use solution for a successful repair.

There are some key considerations needed before a plastic repair is carried out: is the plastic old or new, has it been painted, primed or is it untreated and has it been damaged? These considerations will determine whether the plastic can be repaired and the process needed to achieve a perfect repair. Plastic that is out of shape from any impact will not fit back together properly and may re-crack when trying to refit it back to the vehicle.

This can be solved and addressed at the very start by applying temperature to the bumper as plastic has a memory and will reform with heat.

Cleaning the plastic is the first important step in the process to achieve a successful repair, it is important to remove all dirt, oil, silicone, residue and grease from plastic surfaces that could affect the final finish. Use only a water borne cleaner – PPG’s D8401. Solvent cleaners can penetrate into the bare plastic and cause a poor repair.

Correct preparation of the repair is the next fundamental step. Remove all the paint and then drill a 3mm hole at the end of the crack to stop the crack extending. Then creating a V with a 3mm gap along the crack allows the adhesive to bond properly. Continue with a series of 3mm drill holes at 10mm intervals along the edge of your newly formed ‘V’. These are needed to give an even greater mechanical bond. Making sure the adhesive adheres to the plastic is crucial and shouldn’t be missed in the process.

Always ensure you choose the correct adhesive for the repair you are working on. A rapid adhesive is excellent for small repairs and broken fixings but with a 20-second work time the rapid type is too quick for many repairs. Standard adhesives gives a 90 second work time and a 3.5 minute work time making them ideal for larger repairs. Always allow the adhesive to cure fully as the product  will sand very well. If you need to level the repair use a plastic body filler which has been developed to flex with movement.

Now the plastic component is ready for priming. Remember cleaning is the key to success. Ensure you remove any residue before priming, as this helps ensure the area has the best adhesion for the refinish paint and then apply an anti-static agent – D846 to remove any dust and reduce static charge. The next step is to apply the relevant adhesion promoter – D820. For repaired plastics, you can follow with PPG’s Rapid Greymatic or DP4000 primers. The repair can now be finished using an appropriate colour system, PPG has a wide selection of colour formulations for precise colour matching; guaranteeing you will be able to find a solution for your repair.

Useful info on plastics

Identify if the plastic component is coated with an OEM plastic primer. If supplied in a primer and intact then no plastic primer system is required. Look for signs of overspray on the back of the panel, test a small area on the back of the panel with gunwash. Plastic primers will generally soften or melt with thinners and some plastics may also melt.

Identify the type of plastic the component is made of. For recycling requirements, manufacturers are required to identify the plastic and this is usually found as a short abbreviation inside the component.

Different types of plastic may require different types of painting processes. Some grades of PE (polyetheylene) are considered unpaintable without a special pre-treatment process.

Some plastics are solvent sensitive, they melt and distort with normal refinish systems, e.g. (polystyrene) used for off road spare wheel covers. These require water based cleaners and compliant primers.

Identification codes:

  • PP – Polypropylene
  • EPDM – Ethylene Propylene Diene Modified
  • TEO – Thermoplastic Olefin (Polypropylene)
  • PE – Polyethylene
  • ABS – Acrylonitrile Butadiene Styrene
  • PUR – Polyurethane
  • RIM – Reaction Injection Moulding
  • PBT – Polybutylene terephthalate
  • PC – Polycarbonate
  • PVC – Poly Vinyl Chloride
  • PA – Polyamide (Nylon)
  • PPO – Phenyl Polyoxide
  • GRP – Glass Reinforced Plastic
  • SMC – Sheet Moulded Compound