Estimating Epoxy Coverage for Fabric Application

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 Number Fabric Weight Per Yard* Mixed Epoxy Needed
740 Glass Fabric 4 oz 1.4 fl. oz.
742 Glass Fabric 6 oz 1.61 fl. oz.
729, 731, 732, 733 Glass Tapes 9 oz 1.94 fl. oz.
745 Glass Fabric 10 oz 2.05 fl. oz.
727, 737 Biaxial Fabric 17 oz 2.81 fl. oz.
738 Biaxial Fabric with Mat 23.8 oz 3.55 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:

Estimating Epoxy Amounts on an Optimist Pram

 

Estimating Epoxy needed to fiberglass an Optimist pram.

 

Bow: 322 in2 Transom : 507 in2 Side×2:3784 in2 Bottom:3444 in2 Total sq in: 8057 in2
÷ 144 Total 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 in2 Bow box: 720 in2 Transom:507 in2 Side×2:3784 in2 Bottom:3444 in2
Total sq in: 8777 in2 ÷ 144 Total 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