How much epoxy to fiberglass a 4 × 8 sheet of plywood?
You need about 1.59 quarts (51 fluid ounces) of mixed epoxy to fiberglass one side of a 4 × 8 ft sheet of plywood with one layer of 6 oz cloth and two fill coats — 3.64 pounds by weight, including 15% waste. The cloth itself weighs 1.33 lb.
How to work it out
- 8 ft × 4 ft = 3.56 sq yd × 1 layer × 6 oz/yd² = 21.3 oz of glass
- Wet-out 21.3 oz + 2 fill coats 29.3 oz + 15% = 3.64 lb ÷ SG 1.1 = 1.59 qt
- Mix ratio 2 : 1 by volume, SG A 1.15 / B 0.97 (typical, not published by the maker — type your data sheet’s SGs for exact weights) → Part A 33.8 fl oz (40.6 oz) + Part B 16.9 fl oz (17.1 oz)
Glassing plywood is common for boat decks, cockpit floors, planters, truck-bed boxes and outdoor furniture. On a full 32 sq ft sheet, the two fill coats use more epoxy than the wet-out, because a single light layer of 6 oz cloth needs only its own weight in resin to saturate. The figure here covers one face; glassing both sides roughly doubles it.
Adjust for your project
More options: waste · ratio · SG A …
- Epoxy by weight
- 3.64 lb (58.2 oz)
- Glass weight
- 1.33 lb (21.3 oz)
- Cloth to buy (all layers + 10% overlap)
- 3.91 sq yd (35.2 sq ft)
- When mixing — Part A (resin)
- 33.8 fl oz (1,000 ml)
- When mixing — Part B (hardener)
- 16.9 fl oz (500 ml)
- Part A by weight
- 40.6 oz (1,151 g)
- Part B by weight
- 17.1 oz (485 g)
Epoxy for one layer on a 4 × 8 sheet, by cloth weight
| Cloth | Glass weight | Epoxy by weight | Mixed epoxy needed |
|---|---|---|---|
| 4 oz/yd² | 0.89 lb | 3.13 lb | 1.36 qt |
| 6 oz/yd² | 1.33 lb | 3.64 lb | 1.59 qt |
| 10 oz/yd² | 2.22 lb | 4.66 lb | 2.03 qt |
| 12 oz/yd² | 2.67 lb | 5.17 lb | 2.25 qt |
What to know about glassing a 4 × 8 plywood sheet
Cloth width decides whether you have a seam. Fiberglass cloth is commonly sold in widths around 38, 50 and 60 in. A 50 in roll covers the 48 in sheet in one piece with an inch to spare on each side, so you buy a single 8 ft length plus a little extra to wrap the ends. Narrower cloth means a seam down the sheet: overlap the two pieces an inch or two and feather the step when you sand, or butt them and fair the joint later.
Mix in several small batches, not one big one. The whole job is about 3.6 lb of mixed epoxy, and a full quart sitting in a deep cup heats up from its own exotherm (the heat the resin gives off as it cures) and can start to set long before you reach the far end of the sheet. Pour each batch onto the cloth promptly and spread it with a squeegee, working from the middle out.
Bare plywood is thirsty. If you wet out the cloth straight onto dry wood, the veneer wicks resin out of the glass and leaves white, starved patches. A thin seal coat on the bare wood first, left to go tacky, stops that — budget roughly one extra fill coat’s worth of epoxy for it. Round over the edges with a small radius, too: cloth will not lie flat over a sharp 90° corner and peels up into an air bubble along the edge.
Compared with WEST SYSTEM’s published formula for 6 oz cloth (about 1.61 fl oz per square foot, with three thinner fill coats), this sheet works out to about 51.5 fl oz — within an ounce or so of the calculator’s figure, so either is a sound basis for ordering.
Different size? Use the full Fiberglass Epoxy Calculator.
What you’ll need
- Marine laminating epoxyPremium price
Thinner, stronger-bonding epoxy for wetting out fiberglass and repairing wood. Many use metering pumps at 5:1 or 2:1.
See options on Amazon (opens in a new tab) - Fiberglass cloth (6 oz)Mid-range price
Woven cloth for glassing and repairs. 6 oz is a common all-rounder; lighter cloth drapes better over curves.
See options on Amazon (opens in a new tab) - Notched spreaders & foam brushesBudget price
For pushing a flood coat to the edges and brushing drips off the sides evenly.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much fiberglass cloth do I need for a 4 × 8 sheet of plywood?
One layer on one face is 32 sq ft, about 3.6 sq yd. The calculator adds 10% for overlaps and shows 3.91 sq yd; with 50 in wide cloth you can usually cover the whole face with a single 8 ft length plus a little for wrapping the ends.
How much epoxy to glass a 4x8 plywood sheet with three fill coats?
About 2.04 quarts of mixed epoxy (4.69 lb by weight) for one layer of 6 oz cloth with three fill coats on one face, including waste.
How much epoxy for two layers of 6 oz cloth on a 4x8 sheet?
About 2.25 quarts — 2.67 lb of glass wet out 1:1, plus two fill coats and 15% waste.
How many WEST mini-pump strokes to glass a 4x8 sheet?
About 64 strokes of the WEST SYSTEM 300 mini pumps with 105 resin and 205 or 206 hardener (about 0.8 fl oz mixed per stroke of each pump) for 1.59 qt of mixed epoxy. Pump a few strokes at a time into a cup rather than all at once.
How much epoxy to glass a 4x8 sheet with 4 oz cloth?
About 1.36 quarts. Lighter cloth needs less wet-out resin, but the two fill coats stay the same, so the saving is smaller than the drop in cloth weight suggests.
Sources
- WEST SYSTEM — Estimating Epoxy Coverage for Fabric Application (opens in a new tab) — Coverage formula for cloth: 50:50 resin to fiber, three fill coats, about 15% waste; 6 oz cloth ≈ 1.61 fl oz per sq ft
- Epoxyworks — Calculating Epoxy for Fiberglass Laminates (opens in a new tab) — About 50% resin by weight hand laid, about 38% vacuum bagged; add 15% for waste
- WEST SYSTEM — 300 Mini Pumps (opens in a new tab) — One full stroke of the resin pump and one of the hardener pump: about 0.8 fl oz of resin/hardener with 105/205–206, about 0.9 fl oz with 105/207–209
- Epoxyworks — Avoiding Respiratory Irritation (opens in a new tab) — Dust protection when sanding; never sand partially cured epoxy