This is a common question that has no simple answer. The coverage or yield you get from your mixed epoxy or polyester resin depends partly on your application—are you using it to seal porous wood? Wetting out fiberglass cloth for a layup? Filling the weave? Yield also depends on your experience level because usually, if you have more experience, you'll be more efficient. Greater efficiency usually means less wasted product. But even though epoxy has minimal shrinkage, you should still add in about a 15-20% for waste allowance (from individual technique, drips, spillage, measuring/mixing mistakes, or contamination).
The following are some basic guidelines for epoxy coverage dependent on whether you're sealing wood or wetting out fiberglass.
Sealing bare wood - Coverage will vary based on how porous the wood is. Hardwoods such as teak and ipe are not as porous as woods like marine plywood. Even with a porous wood, some planks or areas will absorb more epoxy than others. Coverage will also depend on how thickly the mixed resin is applied. For example:
- One gallon of mixed epoxy (no waste, no loss) yields:
- About 25.6 square feet at 1/16" thickness
- About 12.8 square feet at 1/8" thickness
- About 6.4 square feet at 1/4" thickness
Wetting out fiberglass - There are different types and weights of fiberglass reinforcement materials, and some take more resin to wet out than others. In general, the heavier the fabric, the more resin you need for wet out.
| Type of Reinforcement | Calculating Mixed Epoxy Amount Needed | Example |
| Fiberglass cloth (rated in oz. per square yard) | Resin amount should equal the total weight of the cloth. | 1 square yard of 6 oz. cloth weighs 6 oz. You need 6 oz. of mixed epoxy to wet out 6 oz. of cloth. |
| Chopped strand mat (CSM) (rated in oz. per square FOOT) | Resin amount needs to be 2 times the total weight of the cloth. | 1.5 oz chopped strand mat requires 2 times its weight in resin, per square foot. 1.5 oz. of CSM needs 3 oz. of mixed epoxy resin for wet out. |
| Biaxial fiberglass cloth (rated in oz. per square yard) | Resin amount needs to be three times the total weight of the cloth. | One square yard of 17 oz. biaxial cloth needs 51 oz. (17 oz. x 3) of mixed epoxy for wet out |
The information above shows how much epoxy you need to wet out one layer of reinforcement material (with 1 coat of epoxy). Keep in mind that it typically takes 3 coats of resin for a typical hand layup: 1 coat of epoxy to wet out the fiberglass, and 2 more coats of epoxy to cover the cloth so no weave pattern is showing (also called 'filling the weave').
The following are general estimates for epoxy coverage when wetting out some common types of fiberglass material. Note that these estimates are based on wetting out one layer.
- 4 oz. fiberglass cloth - One gallon of mixed epoxy wets out approximately 37.5 square yards
- 6 oz. fiberglass cloth - One gallon of mixed epoxy wets out approximately 25 square yards
- 10 oz. fiberglass cloth - One gallon of mixed epoxy wets out approximately 15 square yards
- 1708 biaxial fiberglass cloth with mat backing (23.75 oz per square yard) - One gallon of mixed epoxy wets out approximately 4 square yards
- Fiberglass CSM - One gallon of mixed epoxy wets out approximately 5 square yards
- Fiberglass 18 oz. woven roving - One gallon of mixed epoxy wets out 4.5 square yards
- Fiberglass 24 oz. woven roving - One gallon of mixed epoxy wets out 3.5 square yards
In addition to sealing and wet out, if you'll also be using epoxy to create a filleting material or fairing compound, you need to factor that into your estimate. It's important to note that, if working with polyester or vinyl ester resin, the weight of the resin is on the container, and that's the weight you use in your calculations; if working with epoxy resin, you must factor in the hardener component, and use the weight of the mixed epoxy (resin and hardener). Actual resin coverage varies based on your experience and your fabrication technique.
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