Resins

Every fiberglass resin we stock, and how to tell which one you need

Three chemistries do the work on a boat. Picking between them comes down to what you are bonding to and what the job is worth. All three are here, from quart repair sizes up to 5 gallon, and every one ships with its hardener or catalyst.

Polyester is the default for boat work

Polyester resin is what nearly every production hull was built from, it is the cheapest way to put glass down, and it is the correct partner for chopped strand mat, whose binder needs polyester's styrene to break down. It catalyzes with MEKP measured by percentage, it shrinks as it cures, and it will not bond reliably to cured epoxy.

Epoxy when the bond matters more than the price

Epoxy runs roughly two to three times polyester per mixed gallon and earns it on adhesion. It sticks to wood, to cured polyester, to metal and to itself, it barely shrinks, and it is the only one of the three worth putting into a rotten stringer or a plywood transom. Our house epoxy ships in 2:1 slow, 3:1 medium and 4:1 fast so pot life matches the temperature you are actually working in, and the West System 105 system with 205, 206 or 207 hardener is here for anyone working to a published West schedule.

Vinyl ester sits between them

Vinyl ester catalyzes with MEKP and handles like polyester, but absorbs far less water. It is what to reach for on a barrier layer below the waterline or a blister repair, where polyester is too permeable and epoxy is more than the job needs.

The rule that saves the most rework

Epoxy goes over polyester. Polyester does not go over epoxy. If there is any chance the surface you are laminating onto was repaired with epoxy at some point, use epoxy, because polyester laid over cured epoxy can stay tacky or let go in sheets months later.

Working out how much

The resin calculator sizes the batch from your layup, and the MEKP calculator gives the catalyst dose for your batch and shop temperature. Both are free and neither asks for an email.