Does any one no the maximum open time is before coupling coat can be applied can the open time be days.

Hi, assuming you are talking about the Uni-Mould System. I usually apply the coupling coat when the gel coat is tacky 5/6 hours. But recently I left it for two days (not intentionally). I have also quickened the process by using heat ( 6/7 hours for the whole mould). I am not suggesting that either would be recommend by EC but both moulds have been used for Infusion multiple times and are holding up well.

I usually make my molds from epoxy so the open time is crucial,this is first time using unimo

I have used 2% Catalyst in the past on the gel coat because at 1% the gel coat was taking too long to go off and eating/attacking  the plastic part I was moulding off. 

Carbon Copies Ltd

I having given it two gel coats first coat catalized at 2% and second gelcoat at 1% because I wasn't sure of open time for coupling coat,I think am going to bring part to work and give it coupling coat mid morning then apply main reienforcement about 6 that should be sufficient time.