Estimating how much epoxy is required to wet out fabric is based on the fabric weight and square footage. The table below provides estimates of the amount of epoxy needed to apply 1 sq. ft. of fiberglass cloth followed by two fill coats.

Fabric Product NumberFabric Weight Per Yard*Mixed Epoxy Needed
740 Glass Fabric4 oz1.4 fl. oz.
742 Glass Fabric6 oz1.61 fl. oz.
729, 731, 732, 733 Glass Tapes9 oz1.94 fl. oz.
745 Glass Fabric10 oz2.05 fl. oz.
727, 737 Biaxial Fabric17 oz2.81 fl. oz.
738 Biaxial Fabric with Mat23.8 oz3.55 fl. oz.

*Includes 15% waste factor. More (or less) may be needed depending on the job and personal application technique. The epoxy is applied at room temperature, approximately 72° F.

Estimating Epoxy Amounts

This formula will help you when estimating the amount of mixed epoxy needed to wet out fiberglass cloth (assuming a resin-to-fiber ratio of 50:50) and apply three rolled epoxy coats to fill the weave of the cloth, i.e. “fill coats.” The formula includes a waste factor of approximately 15%; however, more (or less) may be needed depending on the job and personal application technique. The epoxy is applied at standard room temperature, approximately 72° F.

Gallons of mixed epoxy=A× [(Wf×0.00085)+0.0075]

Where:
A=Total area covered by fiberglass. Units are in square feet (ft2)
Wf =Total weight (W) per square yard of fiberglass (f) cloth used in laminate. Units are in ounces per square yard (oz/yd2), i.e. 6 oz fiberglass cloth weighs 6 oz/yd2.

Let’s use the Optimist pram as an example:

diagram of boat sections patterns for estimating epoxy coverage
Bow: 322 in2Transom : 507 in2Side×2:3784 in2Bottom:3444 in2Total sq in: 8057 in2
÷ 144Total outside sq ft:56 ft2

  • The INSIDE is covered with 6 oz fabric and three fill coats. The bow box is covered with 6 oz fabric on one side only.
Bow: 322 in2Bow box: 720 in2Transom:507 in2Side×2:3784 in2Bottom:3444 in2
Total sq in: 8777 in2÷ 144Total inside sq ft:61 ft2
  • Outside calculation 56 ft2 [(12 oz/yd2 × 0.00085) + 0.0075] = 0.99 gal
  • Inside calculation61 ft2 [(6 oz/yd2 × 0.00085) + 0.0075] = 0.77 gal

Total 1.76 gal mixed epoxy

Note: a Group Size B 105 Epoxy resin and hardener makes 1.2 or 1.3 gal of mixed epoxy depending on which hardener. —From “Estimating Epoxy Amounts” by Bruce Niederer, Epoxyworks #18