Vinyl ester resin is chemically similar to polyester resin and they both bond well to each other. Vinyl ester resin also requires a catalyst, MEKP, to be mixed in to initiate the curing process, and the resin and catalyst must be mixed thoroughly before adding any fillers or thickening agents.

When to Use Vinyl Ester Resin 

Vinyl ester resin can be used on the outer laminate layer for blister prevention (instead of iso-polyester resin), and the less expensive polyester resin can be used on the inner laminate layers to add bulk.

Advantages

Vinyl ester resin is much stronger and less prone to blistering because although it’s not as impermeable as epoxy resin, it’s much more water resistant than polyester resins.

Because polyester and vinyl ester resin are compatible chemically, they can be used together in a layup to best advantage.

Vinyl ester resin is also compatible with CSM (fiberglass chopped strand mat), so it dissolves the binder in the CSM and cures to a strong composite. CSM is typically the last laminate layer beneath the gelcoat paint due to its strength and smoothness.

Disadvantages

Not as strong, flexible, or waterproof as laminates created with epoxy resin. Shelf-life should be monitored carefully, because this resin will eventually harden in the container. Once opened, it can harden in approximately three months.

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