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

Most CSM is designed for polyester or vinyl ester resin because the binder in standard mat doesn’t dissolve in epoxy. However, epoxy-compatible chopped strand mat is available and should be used if you’re working with epoxy systems.

To wet out a full 50" wide yard of the 1708 biaxial fiberglass you'll need about 30oz of epoxy resin. This is a thick layup with stitched core and mat, which yields a strong result.

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 your working time and cure time, not the final strength. A fast hardener like West 205 gives a short pot life, around 9 to 15 minutes, and cures quickly, which suits cool weather and small batches. A slow hardener like West 206 stretches working time and cures well in heat. Match the hardener to your temperature and batch size, and keep the ratio the maker 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 (100–120°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, resin has a shelf life. 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 six months to a year, because the styrene and promoters break down. MEKP also weakens over time, so old catalyst can leave resin undercured.