Cobalt Naphthenate is the common accelerator (or promoter) in most polyester resins and should never be brought into direct contact with catalyst (MEKP), outside of the resin mix, as an explosion could result. For safety reasons, general laminating resins are usually supplied pre-promoted and extra accelerator can be added if you require a quicker setting time although, as they are pre-promoted, we usually have to adjust the catalyst level. In this instance, we should be using un-promoted resin and adjusting the amount of accelerator to suit the conditions.  Never add excessive amounts of the accelerator to any resin.