West System Epoxy: 105 With 205, 206 or 207 and When Each Applies

Boat Suppliers

24 September 2026

You are at the shelf with a can of West System 105 resin and three hardeners, and the job decides which one gets pumped. 205 Fast is 5:1 by volume, 9 to 12 minutes of pot life in a 100 g cup at 72°F (22°C), and it keeps curing down to 40°F (4°C): bonding and repair, small batches, cool weather. 206 Slow is the same 5:1 with 20 to 25 minutes, for laminating and big glue-ups in a warm shop, minimum 60°F (16°C). 207 Special Clear is 3:1, 22 to 26 minutes, blush-free with a UV inhibitor, and it exists for clear coating wood and carbon. Here is the full comparison, the mixing rules that keep the cure honest, and what to buy with the resin.

105 resin: the base of the whole system

105 is a clear, amber-tinted, low-odor epoxy resin that has been the marine standard since the Gougeon brothers put it in a can. It does nothing on its own; the 200-series hardener you pair with it sets the cure speed, the working temperature range, the finish clarity and, through the mix ratio, how you meter it. Mixed viscosity at 72°F is 975 cps with 205, 725 cps with 206 and 760 cps with 207, all thin enough to wet out 1708 biaxial and 6 oz cloth and to soak into end grain. Cured, the system runs 6,750 to 7,900 psi tensile depending on the hardener, with a heat deflection temperature around 117 to 123°F (47 to 51°C), which is why a dark epoxy deck in the Florida sun needs a topcoat. What most people type into a search bar as West Systems epoxy is this one resin and the choice below.

Hardener	Ratio by volume	Pot life, 100 g at 72°F	Solid	Working strength	Minimum temp	Blush	Cured tensile	Use
205 Fast	5:1 (5.19:1 by weight)	9 to 12 min	6 to 8 hr	1 to 4 days	40°F (4°C)	Yes	7,900 psi	Bonding, repair, cool weather, small batches
206 Slow	5:1 (5.19:1 by weight)	20 to 25 min	10 to 15 hr	1 to 4 days	60°F (16°C)	Yes	7,300 psi	Laminating, large glue-ups, warm shops
207 Special Clear	3:1 (about 3.7:1 by weight)	22 to 26 min	10 to 15 hr	1 to 4 days	60°F (16°C)	No	6,750 psi	Clear coating wood, carbon, bright finishes

Pot life is measured in a 100 g mass in a cup, and that is the number that matters for how you work. A full quart of 105/205 in a bucket at 85°F will smoke in five minutes. Pour the mix out into a roller tray or spread it on the work as soon as it is stirred and the open time on the surface is several times the pot life in the cup.

205 Fast: repair and bonding, especially when it is cold

205 is the hardener for the jobs where you want to sand or reload the part on the same day: bedding hardware, gluing a block, filling a drilled hole, tabbing a small patch. It cures to a solid in 6 to 8 hours at 72°F and it will still go off at 40°F, which no other hardener in the system does; a winter transom bond in an unheated shop is a 205 job. The tradeoffs are the short pot life, which limits you to cups of a few ounces, and amine blush, the waxy film it sweats in humid air, which must be washed off with water and a scrub pad before sanding or recoating. It is not for clear coating; the cured film has an amber cast and the blush clouds it. West System 205 Fast Hardener comes in A, B and C sizes that match the 105 can sizes.

206 Slow: laminating and anything with a lot of parts

206 doubles the working time to 20 to 25 minutes and cuts the mixed viscosity to 725 cps, which is what you want when you are wetting out four plies of 1708 on a transom, gluing up a laminated tiller with a dozen clamps, or coating a deck in July. It needs the shop at 60°F or better and takes 10 to 15 hours to go solid, so it is a next-day sand. It blushes like 205 and gets the same water wash. On a big layup, 206 is not optional: the fast hardener will gel in the cup before the third ply is wet. West System 206 Slow Hardener is the shelf hardener from May to October in the Southeast and the year-round laminating default in a heated shop.

207 Special Clear: bright finish and carbon

207 is a different ratio, 3:1 by volume, and a different chemistry: it does not blush, it carries a UV inhibitor, and it cures water-clear with a thin film that levels and needs little sanding. It is the hardener for clear coating a wood deck, a laminated tiller, a cold-molded hull, or a cosmetic carbon panel where a cloudy film would ruin the work. You can apply multiple coats in a day without sanding between them as long as the previous coat is still tacky. It is not a substitute for varnish: the UV inhibitor slows yellowing, and for a bright finish that lives outside you still topcoat with a UV varnish. It laminates and bonds fine too, but 205 and 206 are stronger and cheaper for structure. West System 207 Special Clear Hardener comes in SA, SB and SC sizes matched to the 105 cans at the 3:1 ratio.

Mixing: the pumps, the ratio and the stir

The ratio is not adjustable and off-ratio epoxy never fully cures, so meter it rather than eyeball it. The West System 300 Mini Pump Set threads into the resin and hardener cans and delivers the right ratio at one full stroke of resin to one full stroke of hardener, for both the 5:1 (205 and 206) and the 3:1 (207) pairs; the set includes one resin pump and two hardener pumps for that reason. Prime the pumps until a full stroke delivers a full shot, then count strokes. If you weigh instead, use the weight ratio, 5.19:1 for 205 and 206, and not the volume number. Stir for two minutes scraping the sides and bottom, and match the hardener letter to the resin letter: a 205-A or 206-A with a 105-A quart, B with the 0.98 gal, C with the 4.35 gal, so the cans run out together. Epoxy is a skin sensitizer and the dust is fine, so nitrile gloves, eye protection and a fitted P100 respirator with organic vapor cartridges for sanding and any solvent wipe.

404 High Density: the filler for hardware

Neat 105 runs out of a vertical joint and out of a screw hole. For anything that carries load, chainplates, engine mounts, cleats, drilled-and-filled fastener holes, hardware bedding, stir in West System 404 High Density Filler until the mix stands in peaks like peanut butter. 404 is the highest-strength adhesive filler in the range and it is built for cyclic load; it is not a fairing filler, and it sands like concrete, so keep it out of anything you plan to shape. Mix the resin and hardener fully first, then add filler, and you get the full pot life of whichever hardener you chose. For a structural fillet under a stringer tab, 404 with 206 gives you 20 minutes to tool it before the tape goes on. If you need a fillet that sands more easily, fumed silica added to epoxy produces a thickened mix that shapes well and finishes smooth.

What to buy

A repair shop stocks West System 105 Epoxy Resin in the B size, a 206 for laminating and a 205 for cold days and small bonds, a 300 pump set installed on each, and a can of 404. Add 207 only when a clear finish is on the calendar. For quantity, a transom skin of four plies of 1708 on a 20 ft outboard or a deck sheathing job is a resin-calculator problem, not a guess: put the fabric, ply count and coat count into the resin calculator and size the group from there. In cold weather choose 205, in a warm shop or on a big layup choose 206, and for anything you want to look at through the finish choose 207. If you are weighing marine epoxy against a table top system for a project that straddles both worlds, the differences in flexibility, blush and UV resistance are worth reading through before you commit.

Frequently asked questions

Can I mix 205 and 206 hardener together?

Yes. 205 and 206 are both 5:1 with 105 and can be blended in any proportion to land a pot life between 9 and 25 minutes at 72°F. Measure the combined hardener at the 5:1 ratio, not each separately. Do not blend 207 into either; it is 3:1 and a different chemistry, and the ratio math breaks. For most shops, keeping both cans and picking by the day's temperature is simpler.

What is amine blush and how do I get it off?

Blush is a waxy film 205 and 206 sweat as they cure in humid air. It clogs sandpaper and stops the next coat from bonding. Wash the cured surface with plain water and a maroon scrub pad, dry it with clean towels, then sand. Never solvent-wipe blush; it smears. 207 does not blush, which is why it is the hardener for clear multi-coat work.

Is West System epoxy UV resistant?

No. 105 with 205 or 206 chalks and yellows in sunlight within a season. 207 carries a UV inhibitor that slows it, but for a bright finish that lives outside you still topcoat with a UV varnish, two-part polyurethane, or paint. On a hull or deck, treat epoxy as the structure and the barrier, and put a finish over it before launch.

How long before West System epoxy is fully cured?

Solid in 6 to 8 hours with 205 and 10 to 15 hours with 206 or 207 at 72°F; working strength in 1 to 4 days; full cure and full strength around a week at room temperature. Sand and recoat once it is solid and washed, but do not load a bonded chainplate or launch a repaired hull the next day. Cold shops stretch every one of those numbers.

What is the minimum temperature for West System 105?

40°F (4°C) with 205 Fast, 60°F (16°C) with 206 Slow or 207. Below those the cure stalls and the epoxy stays soft for days. Warm the resin and hardener cans to 70°F before pumping, since cold resin pumps short and mixes off ratio, and keep the part warm for the first 24 hours with a lamp or a heated blanket if the shop drops overnight.

What You Need For This Job

West System 105 Epoxy Resin: the base resin, in A, B and C sizes
West System 205 Fast Hardener: 5:1, 9 to 12 minute pot life, cures to 40°F, for bonding and cold weather
West System 206 Slow Hardener: 5:1, 20 to 25 minute pot life, for laminating and warm shops
West System 207 Special Clear Hardener: 3:1, blush-free, for clear coating wood and carbon
West System 300 Mini Pump Set: meters 5:1 and 3:1 one stroke to one stroke
West System 404 High Density Filler: structural filler for hardware bonding and fillets