Silmar 249A & 249-B Polyester Surfboard Resin FAQ

Silmar surfboard resins are industry favorites for their clarity, workability, and professional finish. Whether you choose 249A or 249-B, you get low viscosity for excellent fiberglass wet-out, strong adhesion, and a clean cure. Below are answers to the most common questions about catalyst usage, resin differences, and workability.

1. What MEKP Catalyst Percentage Should I Use with Silmar Surfboard Resin, and What’s the Typical Gel Time?

For surfboard laminations and hot coats at 77°F, catalyze Silmar 249A or 249-B at approximately 1% MEKP. This delivers a gel time of about 11–19 minutes and a peak exotherm of ~265–305°F. Adjust for temperature, mass, and desired working time.

Pro Tip: For hot coats, add Wax Solution (Mod C) at 1 oz per quart of resin to create a sandable finish.

• Catalyst: MEKP at ~1% by volume
• Gel Time: ~11–19 minutes at 77°F
• Peak Exotherm: ~265–305°F

2. Silmar 249A vs 249-B: What’s the Difference for Surfboards?

Silmar 249A is a water-clear, high-UV-stability polyester laminating resin designed to keep bright whites and vibrant colors intact, even in high-sun environments.

Silmar 249-B is identical in performance to 249A but contains an additive with a subtle blue hue. When cured, the blue shifts into a brilliant white finish, enhancing brightness and giving boards a crisp, clean appearance. Perfect for surfboards and composites that need an extra visual pop.

For either resin, remember to use Wax Solution (Mod C) in your hot coat for a proper sanding and polishing surface.

• 249A: Water-clear, high UV resistance
• 249-B: Slight blue in liquid form, cures to brilliant white
• Both: Low viscosity, professional surfboard finish quality

3. How Thin Is Silmar Polyester Surfboard Resin, and Why Does It Wet Out Fiberglass So Well?

At 77°F, Silmar 249A and 249-B measure approximately 400–550 cps (Brookfield RV #2 at 20 rpm). This low viscosity lets the resin quickly saturate fiberglass cloth, ensuring smooth laminations and minimal air entrapment. Both resins cure with exceptional clarity (water-clear for 249A, brilliant white for 249-B).

Pro Tip: Pair with quality surfboard fiberglass cloth and add Wax Solution (Mod C) for your final coat to achieve a sandable, polish-ready finish.

• Viscosity (77°F): ~400–550 cps
• Benefit: Fast wet-out and easy squeegee work
• Finish: Clear or bright white, depending on resin choice

For more tips and technical data, visit our Fiberglass Florida FAQ page or shop our surfboard resins here.