How Do I Do a Hot Coat on a Surfboard Using Silmar 249A or 249-B?

How Do I Do a Hot Coat on a Surfboard Using Silmar 249A or 249-B?

A surfboard hot coat, sometimes called sand resin, is the final resin layer applied before sanding and polishing. It’s made by mixing Silmar 249A or 249-B with Wax Solution (Mod C) before adding your MEKP catalyst. The wax rises to the surface during cure, sealing off air exposure so the resin fully hardens for sanding.

Hot Coat / Sand Resin Mixing Steps

1. Measure your resin (Silmar 249A for water-clear, or 249-B for brilliant white finish).
2. Add Wax Solution (Mod C) at 1 oz per quart of resin.
3. Mix thoroughly, then add MEKP at the recommended percentage (about 1% at 77°F).
4. Apply evenly over the sanded lamination coat using a clean brush.
5. Allow to cure fully, then sand smooth and polish if desired.

Why Add Wax Solution?

• Prevents air inhibition during cure
• Creates a hard, sandable surface
• Ensures a glossy, professional finish after polishing

Pro Tip: Always work in a clean, dust-free environment and avoid over-brushing to prevent streaks or thin spots in your hot coat.

Shop Silmar 249A and 249-B resins and Wax Solution (Mod C) at Fiberglass Florida.