It depends on the resin used in the fairing compound. Fairing compounds typically contain the following:
- Resin - Epoxy, polyester, or vinyl ester
- Hardener (for epoxy) or catalyst (for polyester/vinyl ester) - Activates the resin and ensures that it cures to a hard plastic.
- Low-density filler such as fumed silica (for epoxy resin) or chopped fiber (for polyester/vinyl ester resin) - Thickens the putty so it doesn't sag on vertical or overhead surfaces.
- Additive (such as phenolic microballoons) - Makes the compound easier to sand after curing.
Epoxy fairing compounds are waterproof, and provide better adhesion, superior strength, better resistance to crazing (micro-cracks), and offer the best post-cure bond strength, compared to vinyl ester and polyester fairing compounds.
TotalBoat TotalFair is an easy-to-use, two-component epoxy fairing compound with excellent sag resistance, and is easy to sand when cured—at 80°F, it's sandable in just 3 hours. Use TotalFair above or below the waterline on a variety of substrates, including fiber-reinforced plastics (FRP), wood, aluminum, and steel.
Polyester fairing compounds are great for filling fiberglass dings, dents, and gouges above the waterline, but are not waterproof when cured, so should not be used below the waterline.
Vinyl ester fairing compounds can be used above and below the waterline for filling dents and gouges in fiberglass. Vinyl ester repairs can be finished with gelcoat, or primed and painted.