Epoxy calculator
How much epoxy to buy for a job: the area, the number of coats and the kind of coat in; liters, US gallons and kit sizes out.
Result
Buy: 1 × 6 gallon kit
100 sq ft (9.3 m²) × 3 coats at 80 sq ft a gallon is 14 liters. Plus 15% for waste.
How this is worked out
The area is multiplied by the number of coats and divided by how far a gallon of mixed epoxy goes for that kind of coat. Those spreading rates are middle-of-the-road planning figures for a laminating epoxy put on with a roller:
- Seal coat on bare wood or plywood: about 80 sq ft per US gallon (1.96 m² per liter).
- Wetting out 6 oz (200 g/m²) glass cloth: about 70 sq ft per US gallon (1.72 m² per liter).
- Fill or build-up coat over cured epoxy or cloth: about 105 sq ft per US gallon (2.58 m² per liter).
Bare wood drinks the first coat, cloth needs enough to fill the weave, and a build-up coat over cured epoxy spreads furthest. Heavier cloth, a warm day or a squeegee rather than a roller all move the number. Your epoxy maker’s coverage chart is the better figure once you have chosen a brand.
Fillets. A fillet is a cove of thickened epoxy, and the cross-section of a cove of radius r is r² × (1 − π/4), about 0.215 r². That times the length of the run gives the volume of the mix. Around a third or more of a thickened mix is filler powder, so counting all of it as epoxy overstates what you need a little, which is the right way to be wrong.
Waste. Some is always left in the cup, the roller and the brush. Fifteen percent is a sensible default; a first-time builder mixing small batches may want more.
For a sense of how long the glassing actually takes, the hours people logged are broken down by step, and the blog covers the work in more detail.
Epoxy boats people are logging here
Stitch-and-glue, plywood and strip-built designs with public build logs, where you can see how real builds went.
- Northeaster Dory · 3 logs
- Caladesi Carolina Dory · 2 logs
- Squirt · 2 logs
- 14 ft Rapid Robert · 1 log
- 15' Rangeley Lake Boat · 1 log
- Cabin Skiff · 1 log
Questions people ask
How much epoxy do I need per square foot?
As a planning figure, one mixed US gallon covers about 80 square feet of bare wood as a seal coat, about 70 square feet when wetting out 6 oz glass cloth, and about 105 square feet as a fill coat over cured epoxy. In metric that is roughly 0.5, 0.58 and 0.39 liters per square meter per coat. Your epoxy maker publishes its own figures, and they win.
How many coats of epoxy does a plywood boat need?
A common schedule is one seal coat on bare plywood, or one wet-out coat into the cloth where the hull is glassed, followed by two fill coats to bury the weave. Three coats in all is the usual answer, but follow your designer.
How much extra epoxy should I allow for waste?
Allow 10 to 20 percent. Epoxy left in the mixing cup, in the roller and on the gloves adds up, and running short in the middle of glassing a hull is far worse than having some left over.
How much epoxy do fillets take?
A fillet is a cove of thickened epoxy, and its cross-section is the radius squared times about 0.215. A 3/4 inch radius fillet uses about 1.45 cubic inches per foot, so a gallon of thickened mix runs roughly 160 feet. A third or more of that mix is filler powder, so this calculator overstates the epoxy slightly, on purpose.
What size epoxy kit should I buy?
Buy the fewest kits that hold what you need. Bigger kits cost less per liter, but epoxy has a shelf life once opened, so a small boat is usually better served by a kit close to the right size.