Making small repairs to fiberglass surfaces

When working with fillers it’s important to remember that epoxy fillers are recommended for both above and below the water areas; polyester fillers are suitable for use above the water only. Interlux® Watertite is a two-part epoxy filler, suited to most DIY repairs above and below water.

Step 1: Health and Safety

Before commencing preparatory work, ensure the area you are working in is adequately ventilated. Ensure you are wearing the correct PPE; we recommend safety glasses, goggles or visors, nitrile rubber gloves, overalls (ensuring skin is not exposed) and a face mask.

Step 2: Inspection

Inspect for damage. Small repairs can be tackled easily, but any damage affecting a large area, or affecting the structure or hull integrity, should be referred to a professional for proper assessment.

Step 3: Preparation and Priming

Remove any loose filler or gelcoat and abrade edges to remove loose material. Remove all debris and prime with InterProtect® 2000E or Epoxy Primekote, according to system recommendations provided elsewhere in this guide. Apply Watertite or Interfill® after the first coat of primer.

Step 4: Applying the filler

Mask off the damaged area and apply Watertite using a putty knife or spatula. Allow to cure, following the recommendations provided on the product label.







Once cured, sand with 80-220 grit paper. The finished repair should be smooth and level with the surface. If required a second layer of filler may be applied, repeating the same process. The repaired area can then be primed, ready for painting.

“Working with epoxy fillers?”

  • Two-part epoxy fillers are the most widely used fillers in the yachting industry. They are invariably solvent free. A benefit of being solvent free is that they do not attack the underlying primer.

  • Epoxies must be mixed in the proper ratio. Too much curing agent and they will leave a sticky film on the surface that is not suitable for overcoating. Too little curing agent will weaken the filler and cause it to crumble later on.

  • Below the waterline, epoxy fillers must be used. Polyester fillers should not be used as they have a greater propensity to absorb water.