Chip Brushes for Resin Work: Sizes, Bristles and How Many to Buy
10 November 2026
A 2 inch natural-bristle chip brush is the one you buy by the gross, and the decision on everything else is which narrower widths your work actually needs and how many brushes a job burns. The rule that sizes the order: one brush per batch. Epoxy kicks in the bristles in 20 to 40 minutes and polyester in 15 to 25, and a chip brush that has gone stiff is trash, not a cleanup project. A transom rebuild with 3 to 4 plies of 1708 uses 15 to 20 brushes. Count batches, then buy.
Why natural bristle and not synthetic
Chip brushes are china bristle, which is hog hair, set in a tin ferrule on a raw wood handle. That build is the whole point. Hog bristle does not soften in styrene, acetone, or MEK, so it holds its stiffness in polyester and vinyl ester where a nylon or polyester brush goes limp and starts dragging fibers. It is stiff enough to push resin down through 17 oz biaxial and stipple air out of chopped strand mat. And it is cheap enough that cleaning one in acetone costs more in solvent than the brush is worth.
The one complaint is shedding, and it is real on the cheap end of the market. Before the brush touches resin, flex the bristles back and forth against your palm a dozen times, tap the ferrule on the bench, and pull off anything loose. Wrapping a turn of masking tape around the bristle base right at the ferrule and pulling it off takes the rest. For a stiff stipple brush that moves mat, cut the bristles down to about 3/4 inch (19 mm) with shears.
Chip brush sizes, by what each one does on the bench
1/2 inch. Detail work. Wetting out the edge of a piece of 2 inch tape into a corner, touching in varnish along a masked line, buttering a small bond line, coating a screw hole in a cored deck before the fastener goes back. Rod builders live on these.
1 inch. Patches under 6 inches, hardware bedding, the last inch of a fillet where a spreader cannot reach, and epoxy touch-ups on a coated hull. This is the brush for a 2 oz batch.
1-1/2 inch. Tabbing with 4 and 6 inch tape, small pieces of 1708 on a stringer cap, and wetting out 6 oz cloth around a curve where a 2 inch brush lays too flat.
2 inch. The workhorse. Wetting out 1708, mat, and cloth on flat and mildly curved surfaces, applying a coat of laminating resin ahead of the fabric, brushing gelcoat into a mold corner, and priming. If you only stock one width, it is this one.
2-1/2 inch. Coating. Two or three coats of epoxy on a plywood sole, priming a panel, varnishing a hatch. Wide enough to lay a coat down fast, still cheap enough to throw away.
| Width | Typical batch it matches | Best jobs | Pack |
|---|---|---|---|
| 1/2 in (13 mm) | 1 oz or less | Tape edges, corners, screw holes, rod guides | 36 |
| 1 in (25 mm) | 2 to 4 oz | Small patches, bedding, fillet ends | 36 |
| 1-1/2 in (38 mm) | 4 to 8 oz | Tape tabbing, cloth on curves | 36 |
| 2 in (51 mm) | 8 to 16 oz | 1708, mat, cloth wet-out, gelcoat, priming | 24 |
| 2-1/2 in (64 mm) | 16 oz and up | Coating soles and panels, varnish | 12 |
How many chip brushes a job takes
One brush per batch, and a batch is whatever you can spread before it kicks. In a 75°F (24°C) shop that is 8 to 12 oz of laminating epoxy or about a pint of polyester at 1.5 percent MEKP. From our own job sheets:
A transom rebuild on an 18 to 22 foot outboard boat, 3 to 4 plies of 1708 plus tabbing, runs 15 to 20 two inch brushes and 4 to 6 one inch brushes for the corners. A stringer and floor job on the same boat, mat bed plus two plies of 1708 on each stringer and the sole, runs 25 to 35 two inch brushes. Sheathing a 16 foot canoe in 6 oz cloth with three fill coats runs 8 to 10 brushes, mostly 2-1/2 inch. A 5 yard 1708 and gallon kit uses about 10 brushes. Whatever the count, add 30 percent, because a brush that hits the floor or gets a chunk of cured resin in it is done.
Which packs to buy
For a shop, keep six boxes of 2" Chip Brushes, 24 Pack under the bench; that gross covers a season of repairs at the counts above, and the 2" master case of 24 boxes is the bulk buy. For one transom or a single project, one 24 pack is the right size with a few left over. Add the 1" Chip Brushes, 36 Pack for corners and hardware, and the 1/2" Chip Brushes, 36 Pack if you do tape work, rod work, or varnish lines. The 1-1/2" Chip Brushes, 36 Pack earns its place on tabbing-heavy jobs, and the 2-1/2" Chip Brushes, 12 Pack covers coating and priming.
Using a chip brush on resin
Load the brush a third of the way up the bristles, not to the ferrule, or it drips down the handle and onto your glove. On 1708 and cloth, lay resin ahead of the fabric, set the fabric into it, then push resin through from the top with the flat of the brush and chase the air to the nearest edge. On mat, stipple straight down; stroking pulls the strands apart and leaves a resin-poor spot. Do not go back into a batch that has started to gel, and do not put a used brush back in the can. When you sand cured laminate or work near styrene, wear a fitted P100 respirator with organic vapor cartridges, nitrile gloves, and eye protection.
Frequently asked questions
What size chip brush is best for fiberglass?
Two inch, for almost everything. It matches an 8 to 16 oz batch, wets out 1708, mat, and 6 oz cloth on flat and gently curved surfaces, and it is the size sold by the gross. Keep 1 inch brushes for corners and patches under 6 inches, and 1/2 inch for tape edges and screw holes. A 2-1/2 inch brush only earns its place on coating jobs.
Are natural bristle chip brushes better than synthetic for epoxy and polyester?
Yes for resin work. Hog bristle stays stiff in styrene, acetone, and MEK, so it pushes resin through heavy fabric and stipples mat without going limp. Nylon and polyester bristles soften in polyester and vinyl ester within a batch or two. Synthetics only win for water-based paint, which is not what you are doing with a chip brush in a boat shop.
How do I stop a chip brush from shedding bristles into resin?
Flex the bristles hard against your palm a dozen times, tap the ferrule on the bench, then wrap one turn of masking tape around the bristle base at the ferrule and pull it off. That removes 90 percent of the loose hairs. Any that show up in the laminate get picked out with the brush tip while the resin is still wet; after cure they sand off.
Can I clean a chip brush with acetone and reuse it?
You can, but it does not pay. Cleaning a brush takes 2 to 4 oz of acetone, and once epoxy has started to gel in the bristles, the brush is never fully soft again and drops fibers on the next job. Use one brush per batch and throw it out. The math only changes for a 2-1/2 inch brush on a varnish job where you are recoating every day.
How many chip brushes do I need for a transom rebuild?
Plan on 15 to 20 two inch brushes and 4 to 6 one inch brushes for an 18 to 22 foot outboard transom with 3 to 4 plies of 1708 and tabbing, at one brush per 8 to 16 oz batch. Add 30 percent for drops and a brush that catches a cured chunk. A 24 pack of 2 inch plus a 36 pack of 1 inch covers it.
What You Need For This Job
- 2" Chip Brushes, Master Case: 576 brushes, the shop stock for 1708, mat, and cloth wet-out
- 2" Chip Brushes, 24 Pack: one transom or one project with a few spares
- 1" Chip Brushes, 36 Pack: corners, patches, and hardware bedding
- 1/2" Chip Brushes, 36 Pack: tape edges, screw holes, and varnish lines
- 1-1/2" Chip Brushes, 36 Pack: tabbing with 4 and 6 inch tape
- 2-1/2" Chip Brushes, 12 Pack: coating soles and panels
