To apply TotalBoat Gelcoat by brushing, use a natural bristle brush, with tapered bristles, that's not too stiff and that can tolerate the solvents in the gelcoat. When rolling, we recommend a 1/8" or 1/4" solvent-safe roller cover that won't shed hairs or lint.
If you're using TotalBoat Gelcoat without wax, add paraffin wax as an air-dry additive. For best results, use only the amount of MEKP catalyst needed for the amount of gelcoat you're using and the temperature conditions.
Thinning should not be required for most brushing/rolling applications, but if needed, thin with styrene - don't add more than 15% or yellowing can occur.
Always apply gelcoat in proper conditions - 50-95°F (70-80°F is ideal), with 0-90% relative humidity (RH). So the coating flows properly and self levels, do not apply gelcoat in direct sunlight.