Gelcoat Repair, Epoxy Vs. Poly

Although the debate is still on as to whether polyester or epoxy resins are best for repairing wood and fiberglass boat hulls and car bodies, the majority of hobbyists and professionals now lean toward epoxy resins rather than polyester. The advantages for the craftsman, as well as for the vehicle, make epoxy the more logical choice, although some still use poly resins. The type of fiberglass cloth used, and how it is used, is as important as the choice of resin in boat repairs.

  1. Safety

    • The epoxy resin is a non-flammable substance, as rated by the Department of Transportation, making it safer to use and store than poly, which is rated flammable, both in liquid and gas form. The fumes from epoxy resins are less offensive and toxic than poly. Craftsmen working with poly resin must always wear a respirator. Small or large epoxy jobs completed outdoors do not require a respirator, although many craftsmen still use them. Epoxy is also safer to ship, handle and store, because the components are less volatile. Bonds are long-lasting, and do not delaminate, crack or split over time. Since an epoxy bond is mechanical, rather than chemical like a poly bond, it works best for repairs.

    Curing Time

    • Epoxy resins require the addition of hardeners that range from #1 to #3, or slower curing to faster curing. Poly resins cure more quickly than epoxy, and do not have the flexibility in curing times. Epoxy resins can cure at temperatures as low as 35 degrees Fahrenheit, with no restrictions on the humidity allowed in the air at the time of use. This makes the product more versatile and easier to use.

    Storage

    • Epoxy resins can be stored indefinitely without danger or harm. Poly resins have a shorter shelf-life of about six months to a year, and limited storage flexibility. Poly resins should be kept at temperatures above 60 degrees Fahrenheit, or they lose effectiveness.

    Cost

    • Poly resin has been a staple in the marine industry for decades, and the costs for the product are low. Epoxy is much more expensive by comparison. For example; in 2011, 1 gallon of poly resin was about $26, while a gallon of epoxy resin was about $110. The cost advantage clearly goes to poly resin products.