I tried repairing my mould last night as there were a few pin holes in the surface.

Give it some heat first,see if that kicks off the cure.

Would you suggest a heat gun over the surface for a period of time ?

Normally I would expect it to be cured now, but with the temperatures beginning to fall and potentially slight errors due to small batch sizes, it might well take longer. Heat will help to an extent to finish off the cure process.

If it is only tacky but otherwise hard, then you can sand off the tackyness and should be able to carry on with the repair as normal.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I tried heating the repair areas last night with a heat gun, but seemed to have the opposite effect and make the repair area more tacky than before.

Another method, that could also save you having to mix in the wax additive, is to create sticking plasters from flash or brown packing tape. By sticking a small square onto a larger piece of tape (so that the none sticky section covers the new gelcoat) you can seal-off the repair, which should allow full cure (as long as the catalyst is mixed appropriately).

If done carefully, you can also end up with repair sections that are just proud of the mould surface which should save time on flatting back also