Fiberglass Supply Depot Wax Additive for Gelcoat and Polyester Resins — 4 oz Surfacing Agent, Leaves Sandable Tack-Free Finish

Fiberglass Supply Depot Wax Additive is a surfacing agent mixed into final gelcoat or polyester resin coats to produce a hard, tack-free, sandable finish.

When finishing marine, fiberglass, or composite parts you need the final coat to cure fully to the surface so sanding and polishing are straightforward. This wax additive is formulated to migrate to the top of the cure, creating a thin oxygen-barrier layer that prevents surface tackiness and leaves a smooth, sandable topcoat. It’s designed for use in final gelcoat or polyester resin coats only and is compatible with common formulations when used at recommended dosages.

How does this additive create a tack-free finish?

During the curing process the wax component separates and rises to the surface of the gelcoat where it forms a microscopic film. That film blocks oxygen contact so the resin can cure all the way to the exterior without staying sticky. The end result is a surface that responds well to sanding, polishing, and cosmetic detailing.

• Migrates to surface during polymerization to form a thin barrier
• Prevents oxygen inhibition that causes tackiness
• Leaves a sandable and polishable surface when fully cured

What is the correct way to mix and use it with gelcoat?

Add the wax additive only to the final gelcoat or final polyester topcoat — never to laminating or build-up layers that must chemically bond later. Mix thoroughly at the recommended ratio and still add your usual MEKP catalyst; the wax does not replace hardener. Too much additive can cause surface irregularities, so stick to the guideline or test small batches first.

• Typical dosage: ~4 oz per gallon of gelcoat (about 1 oz per quart)
• Always include MEKP catalyst per gelcoat instructions
• Use only in the final cosmetic/top coat, not in bonding layers

Will this affect sanding, polishing, or subsequent coats?

The wax makes sanding and polishing easier by producing a cured surface free of stickiness, but it creates a barrier that prevents proper chemical bonding for additional gelcoat layers. If you plan to apply more coats, you must mechanically abrade or sand through the wax layer before re-coating. For polishing, the wax layer polishes to a good cosmetic shine once properly sanded and compounded.

• Provides a sand-friendly cured surface for finishing work
• Requires sanding to remove wax barrier before re-coating
• Polishes to a smooth cosmetic appearance after finishing

Are there compatibility or troubleshooting tips I should know?

It’s broadly compatible with polyester gelcoats and resins but always test on a small sample to confirm cure time and surface appearance. Watch dosage carefully: over-adding can lead to defects like fish eyes, uneven migration, or surface mottling. Store and handle per resin safety guidelines and follow catalyst instructions precisely.

• Test small batches for cure time and surface look before large runs
• Avoid excessive dosage to reduce risk of finish defects
• Follow resin and MEKP safety and handling recommendations

Who is this for: Fiberglass builders, marine repair shops, mold makers, and DIY composite enthusiasts aiming for professional cosmetic results on boat hulls, molds, and finished parts. If you need a dependable way to achieve a non-tacky, sandable topcoat for polishing or final cosmetic work, this wax surfacing agent helps speed finishing while producing consistent, high-quality results when used as directed.