West System 105 Epoxy Resin

Choose based on temperature, working time, and project type:

• Best for cool temperatures or quick repairs.
• Ideal for general use in moderate to warm temps.
• For clear finishes and brightwork.
• Best for hot climates and large laminations.

It depends on your application:

• High-strength bonding
• Structural bonding
• Fairing (easy sanding)
• Ultra-lightweight fairing

Yes. Our chopped strand mat works with epoxy for repairs, tabbing, and flat or gently curved panels. The binder that holds the strands together is made to dissolve in polyester and vinyl ester, so in epoxy it stays put: the mat stays stiffer, does not drape as easily into tight curves, and can cure cloudy instead of clear. Roll it firmly until no dry white fibers remain, and for complex shapes use polyester or vinyl ester resin, or a stitched fabric like 1708 biaxial with epoxy.

Plan on about 4 oz of mixed epoxy per square foot of 1708 for a hand layup. A full yard off the 50 in roll is 12.5 sq ft, so that is roughly 50 oz per yard, per ply. Add 15 to 20% for waste, or run the layup through our resin calculator for the exact amount.

Yes. West System 105 must be used with a compatible hardener (205 Fast, 206 Slow, or 207 Special Clear) to cure properly.

Epoxy resin provides better adhesion, moisture resistance, and flexibility compared to polyester resin. While polyester is more economical and widely used in mass production, epoxy is preferred for high-performance applications, repairs, and situations requiring a strong bond.

Follow the specific mix ratio provided by the manufacturer (commonly 2:1 or 1:1 by volume). Mix thoroughly in a clean container, scraping the sides and bottom, until the blend is uniform and streak-free.

The ratio is fixed by the resin and hardener chemistry, not by strength, so each system has its own ratio you must follow exactly. West System uses 5 parts resin to 1 part hardener, while our Boat Suppliers hardeners come in 2:1, 3:1, and 4:1 versions. A lower ratio like 2:1 means more hardener by volume and is easier to measure. Choose cure speed by hardener type, never by changing the ratio.

Amine blush is a waxy film that forms on curing epoxy as it reacts with moisture and carbon dioxide in the air, most often in cool, humid conditions. Left on, it blocks adhesion of the next coat, paint, or gelcoat. Wash the cured surface with plain water and a Scotch-Brite pad, dry it, then sand. West System 207 hardener is formulated to resist blushing.

Hardener speed sets working time and cure time, not final strength. West System 205 Fast gives 9 to 12 minutes of pot life (100 g at 72°F), cures down to 40°F and suits cool shops and small batches. 206 Slow gives 20 to 25 minutes for warm shops and bigger layups, and 209 Extra Slow about 40 to 50 minutes. Always mix at the ratio the system specifies.

Yes, but cold slows the cure and thickens the resin. Below about 60°F most epoxies cure slowly and can stay tacky, and below freezing they may not cure at all. Warm the resin and hardener to room temperature before mixing, heat the work area, and choose a fast hardener for low temperatures. Never add solvent to thin cold epoxy, since that weakens the cured bond.

The best way is to warm it, not add solvent. Stand the resin and hardener in warm water or a warm room and the viscosity drops so it wets out and brushes more easily. Acetone or lacquer thinner does lower viscosity but weakens the cured epoxy and can stop it from fully curing, so keep solvents out of structural mixes. Warm the surface too for a thinner film.

Yes, epoxy resin can be tinted using compatible pigments or dyes. This is often done for cosmetic finishes, artistic projects, or color-coding repairs.

Generally yes, as long as it wasn't frozen repeatedly or for an extended period, but it depends on the product and how it was handled.

What freezing does to epoxy:

• Resin (Part A): Can cause crystallization or cloudiness. This looks alarming but is usually reversible, gentle warming (100 to 120°F water bath) and stirring typically restores it to normal.
• Hardener (Part B): More sensitive. Some hardeners (especially amine-based) can be damaged by freezing, becoming cloudy or separating in ways that don't fully reverse.
• Packaged kits: Pre-measured kits sitting frozen in a warehouse are typically fine, many manufacturers actually ship in cold weather without issue.

Yes. Unopened epoxy resin and hardener usually last one to several years stored cool and sealed, though hardener may darken without losing strength. Polyester resin and gelcoat are shorter lived, often three months to a year depending on the product, because the styrene and promoters break down. MEKP also weakens with age, and old catalyst can leave resin undercured, so check the label.