Can anyone tell me how I can get rid of the tacky surface on polyester? When I laminate stuff, it gets completely hard, and isn't tacky. But when I paint a layer on something, as a top coat, it stays tacky. Even when I apply more hardener than usual!

you need topcoat!

When you laminate, the wax in the mould should cure any tackiness, but if you are painting on resin or gelcoat, you need to add wax to the resin to stop the tackiness.

CFS's website explains all:

CFS

it is air inhibited so that when you are laminating it doesnt fully cure untill the next layer goes on, then the last layer needs to be top coat which isnt air inhibited and cures normally and allows the previous coat to cure.

Thanks.

What's the difference between gelcoat and topcoat? Is topcoat thinner?

gelcoat is also air inhibited like the resin, top coat just has the activator in it to make it cure normally.

Cover it with plastic sheet?