I started a second mould (Unimould system) a few days ago, and the gelcoat is not hardening as it did the first time.

Hi,

It sounds like it's just under-cured (at this point). This is most likely to be a result of incomplete mixing of the MEKP catalyst into the gelcoat but I'd have to see exactly the location of these undercured areas in order to see whether they're consistant with this cause.

If the gelcoat that's not fully cured is feeling a bit rubbery and part cured and you've already got a first layer of gelcoat underneath it (providing a hard surface for the mould) then I think I would take the chance and go ahead with the coupling layers and backing layers. If you've got 27'C ambient plus you run a decent catalyst level (but don't overdo it on the catalyst for the tooling resin otherwise you'll run out of time for the layup!) then I hope and expect there's a good chance that the exotherm from the main reinforcement will cure finish the cure off but I can't guarantee it.

The only worrying thing is that it's not cured after a couple of days which might mean that it's 'stalled' altogether and won't get finished off by the exotherm from the reaction. However, I think I'd be tempted to give it a go!

If you don't want to risk it then the easiest method of removing the gelcoat from the mould is to put a single layer of Chopped Strand Mat and standard GP polyester laminating resin on, wait for it to cure and then pull the whole lot out before starting your gelcoating again.

I hope this helps,

Best regards, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales