Expert advice

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 only suitable for use above the water.

Step 1: Health and safety

Before commencing preparatory work, please ensure the area you are working in is adequately ventilated. Ensure you are wearing the correct Personal Protective Equipment (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 roughen edges to remove any loose material. Remove all debris and prime with an International primer. For an osmosis protection scheme use Interprotect®.

Step 4: Applying the filler

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

Once cured, sand with 80-220 grade paper. The finished repair should be smooth and level with the surface. You may need to apply a second layer of filler, if so, repeat 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. Most of them are solvent free. A benefit of this is that they don’t 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’s not suitable for overcoating. Too little curing agent will weaken the filler and cause it to crumble later on. 
  • You must use epoxy fillers for anything below the waterline. Polyester fillers shouldn’t be used for this as it’s very likely they’ll absorb water.

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