Clear Polyester Surfboard Resin - Silmar 249 with Hardener

Silmar 249 is the industry standard polyester laminating resin for surfboard construction. It’s also used in other composite projects where a clear, durable finish is required.

Yes. Each Silmar 249 clear polyester surfboard resin purchase includes the right amount of MEKP catalyst for the volume you buy. Polyester takes catalyst, not hardener, so you add MEKP by percentage to control cure speed. Follow the catalyst chart for your working temperature, and mix only what you can use before it kicks.

Epoxy resin provides better adhesion, moisture resistance, and flexibility compared to polyester resin. While polyester is more economical and widely used in mass production, epoxy is preferred for high-performance applications, repairs, and situations requiring a strong bond.

Polyester resin is widely used for building and repairing fiberglass boats. It is ideal for laminating fiberglass cloth, molding parts, and creating gelcoat finishes. It’s cost-effective and works well for general-purpose repairs.

At the standard 1.25% MEKP dose and about 77°F, polyester resin gels in roughly 15 to 30 minutes and cures hard over several hours. Warmer temperatures, thicker pours and more catalyst shorten that, and cold lengthens it, so adjust the MEKP dose for your shop temperature.

The standard dose is 1.25% MEKP by volume at 77°F, about 12 cc per quart or 47 cc (1.6 fl oz) per gallon. Use more when it is cold and less in heat, but stay between 1% and 2%: below 1% the resin can stay soft, and above 2% it can crack, smoke or kick before you can work it. Measure in cc with a dispenser, not drops.

Laminating (layup) resin stays slightly tacky as it cures so the next layer of glass bonds chemically without sanding. Finishing resin has a wax or surfacing agent that rises to the top, sealing out air so the last coat cures hard and sands clean. Most marine polyester is laminating resin, so add surfacing wax to the final coat when you are ready to sand and finish.

Yes, polyester resin can be tinted using compatible pigments. This is often done to match gelcoat colors or create custom finishes.

No, you should not use polyester resin on EPS foam (expanded polystyrene). Polyester resin contains styrene, a solvent that dissolves EPS foam on contact. This reaction will ruin your foam core and release harmful fumes. If you're working with EPS foam, for example, in surfboard shaping or foam core laminates, you should instead use epoxy resin, which is chemically compatible and safe for EPS.

Yes. Unopened epoxy resin and hardener usually last one to several years stored cool and sealed, though hardener may darken without losing strength. Polyester resin and gelcoat are shorter lived, often three months to a year depending on the product, because the styrene and promoters break down. MEKP also weakens with age, and old catalyst can leave resin undercured, so check the label.