The gelcoat you are buying is an Isophthalic, NPG gelcoat with or without wax additive.
The gelcoat without wax is used for layups when you want the initial layer of gelcoat to remain tacky to the touch while you're laying reinforcement plies on top in order to create a strong chemical bond in the laminate. If you use unwaxed gelcoat as the finish coating, you must spray PVA (polyvinyl alcohol) over it or use wax paper or some other means to effect a proper cure.
The gelcoat with wax is used for an air dry post-applied application. The wax additive rises to the surface, making a film that creates an air barrier, allowing the final gelcoat layer to cure properly.
Mixing instructions depend on the temperature and preferable dry times. The higher percentage of catalyst, the faster it will dry. Air and surface temperature will also affect the drying of the gelcoat. The colder the air temperature, the higher the percentage of catalyst you should use. Do not go below 1/2% or above 2%.
1 mL = 1 cc
If using a wooden mixing stick, place the stick in the resin before adding catalyst so the wood doesn't absorb the catalyst.
- 1/2% - (79-85 F)
Quart: 4-6 cc, Gallon: 23-26 cc, 5 Gallon: 110-130 cc
- 1% - (72-78 F)
Quart: 8-12 cc, Gallon: 42-47 cc, 5 Gallon: 220-230 cc
- 1 1/4% - (66-71 F)
Quart: 11-14 cc, Gallon: 55-60 cc, 5 Gallon: 275-285 cc
- 1 1/2% - (61-65 F)
Quart: 13-16 cc, Gallon: 65-70 cc, 5 Gallon: 335-345 cc
- 2% - (55-60 F)
Quart: 17-21 cc, Gallon: 86-94 cc, 5 Gallon: 450-460 cc
Directions for Wax Additive (sold separately)
Wax additive is a mixture of paraffin and styrene. When adding it to gelcoat, you must also add the MEKP catalyst/hardener. Wax additive is added to the gelcoat on the final layer of a wet layup to create a tack-free surface that sands easily before applying the finish coating. Wax additive is not needed when additional layers or gelcoat are applied on top. Note that in temperatures below 70°F, the paraffin can solidify in the container. Place the container in the sun or in front of a lamp to liquefy. USE CAUTION - WAX ADDITIVE IS FLAMMABLE!
Wax additive is available in 1 oz. and 4 oz. bottles. For convenience, the 1 oz. bottle is recommended for use with the Quart size container of gelcoat, and the 4 oz. bottle is for use with the Gallon container of gelcoat. Refer to the table below for how much wax additive to add to gelcoat without wax. Too much wax additive will result in fish eye and other undesirable results.