#70 Styrene Monomer is the recommended and accepted thinner for polyester resins and gel coats. Most gel coats can be thinned 2-5% to make them suitable for heavy spray equipment or other special purposes.  

#69 MEKP is required with all Polyester Resins, Gel Coats and Vinyl Ester Resin. It is required in different concentrations as defined for each resin product. Each resin product is available as a kit with the correct amount of hardener. However, hardener may be purchased individually as shown here. 

# 71 Styrene Wax is a 5% solution of paraffin dissolved in styrene that may be added to non waxed polyester resins and gel coats to prevent the prolonged tackiness associated with thin sections of polyesters. If the resin contains paraffins, the wax will rise to the surface and protect the curing resin from the inhibiting action of the air. However, if the resin is allowed to fully cure, the paraffins on the surface will prevent adhesion of further coats of resin and must be sanded off prior to additional applications. We recommend adding #71 at 5% for thin coatings. Use with #1040 Hi-Gloss Additive when performing repairs below the water line.