Catalyst – MEKP (Methyl Ethyl Ketone Peroxide) is normally a clear liquid and must be handled with extreme care. Polyester resin will not harden without catalyst. The amount of catalyst added to the resin is critical and it is normally used in a ratio of 1-2% by weight of the total polyester resin. As a rule of thumb, 20mls of catalyst is usually needed for 1kg of resin. Accurate measurement is important because a small increase or decrease of the amount of catalyst can have a large effect on the working time of the resin.

   The catalysts used with polyester resins are almost invariably organic peroxides.   These are unstable and should be treated with the greatest caution.  They are all irritating to the skin and cause burns unless washed off immediately.   Injury can be more serious if catalyst is splashed into the eyes.   Immediate treatment in such cases is to wash out the eyes continuously with plain water or weak bicarbonate solution.