Styrene - Thinner for Polyester Resins and Gelcoats

SKU:SM-STY010

$10.99 USD

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89 in stock

Size: Pint (16oz)

Pint (16oz) Quart (32oz) Gallon 5 Gallon

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Styrene monomer is the right thinner for polyester resin and gelcoat, and it is not interchangeable with acetone. Acetone dilutes and evaporates out, which weakens the cure. Styrene is reactive: it becomes part of the cured polymer, so thinning with it does not leave the laminate short of resin.

Spraying gelcoat. Around 10 percent by volume brings viscosity down to where a gun will atomize it properly.
Brush and roll flow-out. A small addition helps gelcoat lay down smooth instead of holding brush marks.
Penetrating porous surfaces. Thinned resin wicks into a porous substrate instead of bridging over it.
Dose: 5 to 10 percent by volume. More than that starts costing you cure and physical properties.
Not for epoxy. Styrene has nothing to react with in an epoxy system.
Sizes: pint, quart, gallon and 5 gallon.

Work outdoors or with real ventilation and a P100 with organic vapor cartridges. Read the SDS before you open it.

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Technical Specifications

Mix Thin 5-10% by volume (≈10% for spraying gelcoat)

Resin TypeReactive thinner for polyester resins & gelcoats (not for epoxy)

Mix RatioThin 5-10% by volume (≈10% for spraying gelcoat)

Best ForSpraying gelcoat, smoother brush/roll flow-out, penetrating porous surfaces

How do I thin gelcoat for spraying?

Thin polyester gelcoat with styrene, not acetone, at about 5% to 10% by volume. Styrene lowers viscosity so the gelcoat atomizes and flows out smoothly while keeping the resin chemistry intact, whereas acetone just flashes off and can leave the film weak and porous. Add the styrene before the MEKP, and stay at or below 10% so you do not weaken the cured coat.