Automakers are increasing the use of composite plastics such as carbon fiber, fiberglass and sheet-molded compound (SMC) in vehicle construction, and that means collision repair technicians need to know their repair options and how to do them correctly.
Initial attempts with resins and fiberglass matting either failed or had read-through. Technicians replaced large component pieces to deal with small, locally damaged areas – inefficient and very costly, particularly for high-volume vehicles.
Repair adhesives specifically formulated for composites now enable technicians to fix a small, damaged area on panels and hoods rather than replacing the whole part. They offer advantages such as lightweighting, bonding dissimilar materials, aesthetics and reducing noise vibration and harshness (NVH). It also creates a bond as strong – if not stronger – than rivets and welds.
The process for using repair adhesives is pretty straightforward, but technicians need to follow these steps before moving ahead with any repair:
1. Determine the type of repair needed – structural or cosmetic.
- Structural repair: Any kind of cracking of the plastic, fine “spider webbing” cracks, or a hole – i.e. anything disruptive to the composite behind the actual surface requires a true repair.
- Cosmetic repair: An extension of the structural repair process – i.e. scratch, gouge or damage not in the fiber of the substrate or fiber vest.
2. Create a patch: If a composite has been compromised, reinforcement on the back side is needed. Apply an initial patch to the damaged area and grind out any broken material or fabricating a missing piece. A pyramid patch may be used to fill in the hole.
- Use multiple layers of fiberglass repair cloth and heavily saturate it with the plastic panel repair adhesive. Fiberglass cloth is essential to controlling expansion and contraction in hot and cold weather.
- The more fiberglass placed in the hole to achieve a thickness similar to the original panel, the better the repair.
3. Roll the edges of the patch and eliminate any air and sharp edges. Proper taper will eliminate a “halo effect” or “read-through” at the edges of the repair and provide strength. Leaving air pockets also may cause future layers to pop or result in paint issues.
4. Heat cure the patch. After building the patch to the proper level, a full heat a cure at 180-degrees-F for 60 minutes must be done. The 60-minute cure time begins when the surface reaches 180-degrees-F not when the heat is first applied.
At the end of the 60 minutes, the epoxy has been completely cured and makes the repair undetectable in the future, protecting against a ‘halo’ in the future. A full heat cure at the proper temperature for the right amount of time ensures that the repair is complete and will never show through.