Gelcoat & Filler

Gelcoat is the right choice if the surface needs to regain a hard, glossy topcoat (e.g., scratches, small chips in the gelcoat). Filler is ideal when material is missing or a surface needs to be built up and shaped first (dents, breakouts, edges). The standard practice is often to first fill and shape the area, then finish with gelcoat or paint as a topcoat.

In the boating industry, 2K systems are standard because they are durable and resilient. Polyester gelcoat is typically used as the original surface on many fiberglass boats. Epoxy filler is frequently used when maximum adhesion and moisture resistance are required or the substrate is critical. The decisive factors are the substrate, the location (above/below the waterline), and the desired final appearance.

Many repair kits are available in common white shades, e.g., pure white (RAL 9010) or cream white (RAL 9001). In practice, gelcoat can deviate from the original shade due to UV aging and polishing. For visible areas, it’s worth doing a test dab in an inconspicuous spot. On older boats, a slightly “warmer” shade is often closer to the existing finish than a very pure white.

Adhesion depends entirely on the preparation: Clean and dry the damaged area, sand it down (to increase the surface area), and thoroughly remove dust and grease. Remove any loose or chalky layers. For deeper damage, lightly chamfer the edges. Only then should you mix and apply the product—2K products have a limited pot life.

1) Prepare the damaged area (sand/degrease). 2) Mix the material correctly (2-component, observe mixing ratio). 3) Apply in thin layers, slightly overfilling if necessary. 4) Allow to cure. 5) Sand in stages (coarse → fine). 6) For gelcoat: polish to finish or protect with paint/coating depending on the finish. This creates a smooth, visually clean surface.

In general, gelcoat is a robust surface, but below the waterline, moisture resistance and a suitable system configuration are particularly important. For continuous contact with water, epoxy-based systems (e.g., epoxy filler + barrier coat) are often the safer choice. Therefore, check the manufacturer’s specifications for the specific product and the planned system (primer/barrier coat/antifouling).

After curing, clean the surface regularly, remove salt and dirt, and—above the waterline—polish or protect as needed. Occasionally inspect heavily used areas (cockpit, deck edges, swim platform) for new cracks or chips. If repaired early, damage remains minor and the surface is maintained long-term.