This tutorial is a straightforward guide for beginners on how to repair a small polyurethane (poly) surfboard ding, such as a crack in the rail. It covers the correct use of poly resin, cleaning, and preparation steps.
Key Takeaways & Tips
Clean Wax Contamination
If the ding is contaminated with wax, first use a heat gun on a low, moving heat to soften the wax. Then, wipe off the residue using a wax and grease remover (such as engine degreaser) to ensure the resin adheres properly.
Step 1: Prep the Area
Sand well beyond the ding using 120 grit sandpaper (using a soft pad for the rails). This ensures there is enough rough surface area to apply the fiberglass cloth and resin.
Step 2: Create a Resin Dam
Use masking tape to create a wall (resin dam) around the rail, positioned as close to the ding as possible. This contains the resin, minimizes running, and reduces the amount of final sanding needed.
Step 3: Fill with Resin (Sanding Resin)
Fill the repair area with sanding resin. Sanding resin contains a wax additive that floats to the surface and creates a barrier against air, allowing it to cure hard enough to sand without being sticky (unlike laminating resin).
Step 4: Lamination (Two Patches)
Laminate the fiberglass cloth using laminating resin. Use two patches: a smaller 4oz patch directly over the ding, and a larger 2oz patch over the first. This is a safety measure against over-sanding the top patch.
Step 5: Final Sanding & Buff
Use 240 grit sandpaper on the orbital to remove the resin edges. Then, switch to 320 grit, and finish with a wet sand (320-480 grit) for a smooth finish. Buffing the entire section ensures the repair blends in seamlessly.
Common Mistakes to Avoid
Using Laminating Resin as Final Coat
Assuming laminating resin can be sanded. Laminating resin will remain sticky even after it cures, making it impossible to sand. Always use sanding resin (or add wax additive) for the final coat.
Over-Sanding
The risk when final sanding is removing too much resin and sanding down to the weave of your fiberglass cloth. Using two layers of patches provides a safety net against this mistake.
Not Buffing the Section
Only buffing the repair area. The whole section (e.g., the front third of the board) must be buffed or wet-sanded for the same finish, otherwise the repair will stand out compared to the rest of the board.