Back To Basics: Resin Selections – Part 2 – Polyester & Vinyl Ester Resins

In Part 1 of this Back To Basics series on resins we examined Epoxy resins. Next up on the slate is Polyester resins, the most commonly used resin around & Vinyl Ester resins.

Because Epoxy resins are so expensive, much of the marine industry uses Polyester resins for larger parts and for fabrication of boat hulls. However, polyester resins are not limited to boat hulls or the marine industry. Polyester resins are in fact the most common resin used in the world.

Polyester resins generally have a lower viscosity and have a two-part curing system that is not controlled by air to cure. A “laminating resin” provides tack for layup and generally allows for heavier build-up of fabric layers before applying a final coat of “finishing resin” for cure. Polyester resin uses an acid (catalyst) to allow for accelerated curing at room temperatures. The selected mixture of these resin components allows for cure times to be manipulated for time needed of the part’s layup process.

Overall, polyester resins provide a lower cost solution that is compatible with impressive surface finishes such as gelcoat. However, polyester resins are weaker and have a shorter shelf time than epoxy. Shelf life of most polyester resins are less than a year compared to the three years of most epoxies. Polyester resins are typically not as waterproof as epoxies.

Vinyl Ester resins perform optimally when in conjunction with polyester resins. Vinyl Ester and Polyester are highly similar in chemical makeup and bond well to each other. For instance, it can be as an outer layer to provide chemical protection and additional strength and blister protection in a polyester resin system. These advantages together provide the opportunity for a high-performance composite whether using Kevlar or Fiberglass. High performance boat manufacturers across the nation continue to use these resins to push the limits of what is possible on the water.

Optimal use of Polyester & Vinyl Ester Resins: Most polyester and vinyl ester resins carry a much lower viscosity. This allows it to run through even the thickest Fiberglass (CSM). When used together the material will wet out easily, provide strength to a composite that will take a beating, all while providing a lower cost solution.

In the marine industry for example, FG CSM’s advantage lies within its ability to utilize the friction between each fiberglass strand to absorb most any energy placed upon it. Application polyester or vinyl ester resin is the most effective way to utilize this material.