Resin Boat Talk
Revised by BoatUS editors in June 2012
Polyester, epoxy, and vinylester resins are the basis of barrier coats and fillers. The viscosity of all three allows for an easy, flowing application. Several types of thickening and strengthening products are available, such as reinforced short-strand glass fibers, micro balloons and powder like fillers, which turn the products from a thin, syrupy consistency to a thick putty.
How It Works:
Combines with the catalyst Methyl Ethyl Ketone Peroxide (MEKP) to create a hardened product.
Repairing any polyester product, including most fiberglass boats.
The least expensive of the three resins, polyester can be used over a broader range of temperatures than vinylester. It's not necessarily good for bonding to vinylester or epoxy. It's most suitable for above waterline repairs because it tends to let water pass through more easily than epoxy or vinylester, so it's more prone to blistering.
How It Works:
Cures basically in the same manner as two-part polyester resin, but uses different chemical bases that provide better adhesion, strength, hardness, durability and water resistance.
Wood, plastic, and fiberglass repairs above or below the waterline and as a barrier coat.
Epoxy won't blister like polyester because it absorbs less water. If your original repair was made with an epoxy, then it's best to stay with an epoxy. Epoxy is more expensive and tends to take longer to cure than polyester and vinylester — generally 24 hours between coats. Meticulous surface preparation is required. You must sand the surface free of amine blushes (which come to the surface during the curing process) before applying gelcoat, primer, and paint. Apply 4-6 hours after sanding. Not recommended for use when you have a minimum amount of time. Between applications the surface will become "waxy" if you wait too long, which will keep the next application from adhering as it should. Follow product instructions.