Carbon Fiber Fabric Layup Guide: Plies, Epoxy Ratio and Cut Size

Boat Suppliers

15 October 2026

Laying up carbon fiber fabric by hand is a resin-control job, not a strength job. The fabric carbon fiber shops use for skins and small parts is 5.7 oz/yd2 (193 g/m2) 3K 2x2 twill, it cures to about 0.010 to 0.012 in (0.25 to 0.3 mm) per ply, and it wants roughly its own weight in mixed epoxy. Count plies to reach thickness, mix by the weight ratio on the can, and squeegee until the fabric is translucent with no white spots. Here is the sequence, the numbers and the cut to buy for each part.

Cutting carbon without wrecking the weave

Twill moves on the bias the moment a tow is cut loose. Lay the fabric flat on a clean board, run 1 in masking tape along both sides of every cut line, and cut down the center of the tape with a rotary cutter or sharp shears. The tape stays on until the ply is placed and half wet out, then peels off the trimmed edge. Our strips and panels arrive with taped edges for exactly this reason. Keep 1 in of trim past the finished edge on every side and carry the fabric rolled, never folded; a fold crease shows through a clear finish forever.

Resin: epoxy only, mixed by weight

Carbon sizing is formulated for epoxy. Polyester and vinyl ester cure on it but bond poorly, so treat them as cosmetic only. A thin laminating epoxy with a 20 to 30 minute pot life at 77F (25C) gives you time to place a 24 x 60 panel; a thin 2:1 laminating kit is built for wet-out, and its pot life and cure schedule are on the TDS in the box. Mix in a graduated cup, weigh both parts if the can gives a weight ratio, and pour the mixed resin out into a shallow tray so it does not exotherm in the cup.

Cut	Area	Mixed epoxy per ply	Plus one fill coat
12 in x 12 in square	1 sq ft	0.6 oz (18 g)	1 oz (28 g)
6 in x 5 ft strip	2.5 sq ft	1.6 oz (45 g)	2.5 oz (70 g)
12 in x 5 ft strip	5 sq ft	3.2 oz (90 g)	5 oz (140 g)
24 in x 60 in panel	10 sq ft	6.3 oz (180 g)	10 oz (280 g)

Those figures assume a 1:1 fabric-to-resin weight in a hand layup. A practiced squeegee hand gets close to 0.8:1; vacuum bagging gets to 0.6:1 and pulls the ply thinner. Whatever you plan, add 15% for the cup and the brush and confirm the total in the resin calculator.

Wet-out sequence that avoids pinholes and dry spots

Seal and release the mold or the part surface: mold wax buffed dry, or a coat of PVA if you do not trust the wax.
Roll a thin coat of mixed epoxy onto the surface first. Dry fabric on a dry surface is where pinholes start.
Lay the ply from one edge, letting it fall onto the resin. Do not drag it into position; lift and re-set.
Squeegee from the center out with light pressure. The weave goes from dull black to glossy translucent when it is wet through. White specks are dry filaments; add a little resin there, never more pressure.
Stack the next ply while the first is still wet, orienting it 45 degrees to the ply below for a stiffer, more isotropic panel.
Finish with a squeegee pass that pulls the excess off the surface. A resin-rich skin looks glossy in the cup and cloudy after cure.

Work between 65 and 85F (18 and 29C). Cold epoxy climbs in viscosity and leaves air in the tow crossovers; hot epoxy kicks in the cup. On a big panel, mix 8 oz at a time.

How many plies for the part

Part	Plies of 3K twill	Cured thickness	Fabric to buy
Cosmetic skin over an existing part	1	0.010 in	One uncut piece sized to the surface plus trim
Dash face, hatch lid, cover panel	3 to 4	0.035 to 0.045 in	12 in x 5 ft strip cross-cut into plies
Bracket, seat pan, structural panel	6 to 8	0.06 to 0.09 in	24 in x 60 in panel
Tube or tiller wrap	2 to 3 wraps	0.02 to 0.035 in	6 in x 5 ft strip cut to the circumference plus 1 in overlap
Knife scales, small trim	8 to 12 over a core	0.09 to 0.14 in	12 in squares

For a first part, the Carbon Fiber Square 12 in x 12 in - 5.7oz 3K 2x2 Twill is cheap tuition. For a panel with a show face, buy the Carbon Fiber Fabric Strip 12 in x 5 ft - 5.7oz 3K 2x2 Twill, Taped Edges and cut the plies from it; for anything that needs six plies or a 24 in dimension, the Carbon Fiber Fabric Cut 24 in x 60 in - 5.7oz 3K 2x2 Twill, Taped Edges is the buy.

Cure, fill coats and finishing a show surface

Leave the layup alone until it is hard enough that a fingernail does not mark it, typically 12 to 24 hours at 77F depending on the hardener, then recoat with a fill coat while it is still within the recoat window on the TDS, or wash off the amine blush and scuff with 220 if you missed it. Two fill coats bury the weave texture; sand the second one flat with 320 then 400 wet, never touching the fibers, because a sanded tow turns gray and cannot be fixed. Top with a 2K urethane clear with UV absorbers, since epoxy yellows and chalks in sunlight while the carbon under it does not.

Carbon dust is conductive and gets into everything, so cut and sand cured parts wet or under extraction, and wear a fitted P100 respirator with organic vapor cartridges, nitrile gloves and eye protection for the epoxy.

Frequently asked questions

How much epoxy do I need for carbon fiber fabric?

Plan on the fabric's own weight in mixed epoxy per ply: 5.7 oz (160 g) per square yard of 3K twill, which is about 6.3 oz for a 24 in x 60 in panel and 0.6 oz for a 12 in square. Add 15% for waste and a fill coat equal to about half a ply's resin on any show surface. A 48 oz kit covers a 4-ply 24 x 60 panel with fill coats and waste.

Why does my carbon fiber layup have white spots?

White specks are dry filaments at the tow crossovers, caused by placing fabric on a dry surface or squeegeeing with too much pressure and too little resin. Roll a thin coat of epoxy on the mold before the first ply goes down, keep the shop above 65F (18C) so the resin stays thin, and dab resin onto a dry spot rather than pressing harder. A ply is done when the whole weave reads glossy and translucent.

Can I sand carbon fiber after it cures?

Sand the fill coats, never the fabric. Build two clear fill coats over the last ply, then sand with 320 followed by 400 wet until flat, staying at least 0.005 in above the weave. A tow that gets sanded turns gray and shows through any clear. If you sand through, add another fill coat and start over; there is no other fix.

Do I need to vacuum bag carbon fiber fabric?

Not for panels under about 6 plies or cosmetic skins. A careful hand layup reaches roughly 45% fiber volume, a bag gets to 55 to 60% and pulls each ply from 0.011 in to about 0.008 in. Bag when the part is structural and weight matters, or when it has deep compound curves the fabric will not hold by itself. For a first part, hand lay it and add one extra ply.

What cut size of carbon fiber fabric should I buy?

Match the show ply to the largest surface dimension plus 1 in of trim per side, and cut inner plies from a strip. A 6 in x 5 ft strip does a tiller or a set of tubes, a 12 in x 5 ft strip cuts into five 12 in plies for a dash face, and a 24 in x 60 in panel gives you 10 sq ft for a seat pan or a day of parts.