Are you having issues applying a gelcoat, resin or paint that uses MEKP as a catalyst? The first things you should evaluate are the ambient temperature and the temperature of your material.
When applying any type of coating it is important that you meet the temperature requirements specific to that product. This information can typically be found on the product's TDS (technical data sheet) or on the label.
Typically, coatings should be applied in good weather when air and surface temperatures are above 50°F for most paints and 60°F for epoxy, resin, and gelcoats. If possible, bring the material to the 70-80°F temperature range prior to mixing and application.
Store the coatings inside to avoid fluctuations in temperature. Don't let coatings freeze as this may alter the chemical integrity of the products, and in hot conditions be sure to keep the coatings out of direct sunlight.
Resins and gelcoats that require MEKP (Methyl Ethyl Ketone Peroxide) to cure will require more MEKP in cooler conditions, and less MEKP in warmer conditions. The table below shows generally appropriate guidelines, but be sure to double check the product's TDS sheet: