Here's why and what should be done instead:
Why Fiberglass Resin is NOT a Good Rust Repair:
* Doesn't address the root cause: Rust is oxidation, and fiberglass resin simply covers it up. The rust will continue to expand and weaken the metal underneath, leading to further damage and eventual structural failure.
* Poor adhesion to rust: Resin needs a clean, sound metal surface to adhere properly. Rust creates a flaky, inconsistent surface that prevents good bonding.
* Lack of flexibility: Fiberglass is relatively rigid. The body of a car flexes, and a rigid fiberglass repair will likely crack or separate from the metal over time.
The Correct Approach to Repairing Car Rust:
1. Rust Removal: This is the *crucial* first step. You need to remove all the rust, down to bare, clean metal. Methods include:
* Wire wheel: For surface rust.
* Sandblasting: For more serious rust.
* Angle grinder with sanding discs: For medium to serious rust. Use caution to avoid damaging the surrounding metal.
* Chemical rust converters: These convert rust into a paintable surface, but might not be suitable for all rust levels.
2. Surface Preparation: After removing the rust, you need to prepare the surface for repair. This involves:
* Cleaning: Remove any remaining rust particles, dust, and debris. Use a wire brush, degreaser, and possibly a solvent.
* Priming: Apply a rust-inhibiting primer to the clean metal. This helps prevent further rust formation and provides a good surface for the body filler.
3. Body Filler (optional): If there are significant pits or holes after rust removal, you might use body filler to smooth out the surface. This is a separate product from fiberglass resin.
4. Fiberglass (if needed): Only *after* steps 1-3, and only if there are large holes that cannot be filled with body filler, can you consider using fiberglass. Fiberglass cloth is embedded in resin and used to create a patch over the hole. This patch should be integrated smoothly into the surrounding metal using body filler.
5. Sanding and Priming: Once the body filler and fiberglass (if used) are cured, you sand the area smooth, and apply several coats of high-quality automotive primer.
6. Painting: Finally, apply a matching automotive paint and clear coat to finish the repair.
In short: Fiberglass resin is a supplementary material in advanced rust repair, not a primary solution. Proper rust removal and surface preparation are paramount to a successful and lasting repair. If you're not comfortable with these steps, it's best to consult a professional body shop.
