Just on with this now.  I've altered the plug quite a bit which has a polyester gelcoat finish. Just been through all the grits to 1200 - is it best to polish it and if so with what type of polish? Or just put on mould wax then a few layers of easy lease then do the uni moulding ?  When the part comes out, then wet sand and polish the mould?  The polish question still applies though. Would automotive T-Cut be ok for example? Or would it just be better for the finished result to get it painted in 2 pack polyurethane paint?

Lastly, I'm still up in the air about how many layers of reinforcement to use.  Resin is epoxy, standard wet layup (not infusion), my (3mm) coremat arrived from easy comp. plus the carbon etc.  so I'm wondering if one layer either side of the coremat will give a light but stiff enough fairing? Or better to use 3 layers etc?  Can anyone advise?  It definitely needs the coremat though as it'll be at high speed offroad (it's a rally fairing) so subject to a lot of vibration etc.

Hi Mike,

Just been through all the grits to 1200 - is it best to polish it and if so with what type of polish? Or just put on mould wax then a few layers of easy lease then do the uni moulding ? When the part comes out, then wet sand and polish the mould?

Always get your pattern as perfect as you can, it's far better and far easier to get a perfect finish on a male pattern than it is on a female mould. Female moulds are, by their nature, concave which is much harder to flat and polish than a convex shape. Also, it's nicer to not be rubbing bag the gelcoat on the mould surface if you can avoid it.

As for which polish, T-Cut is really not used at all in the composites industry and has an oily/solvent residue which doesn't work well with release agents. Also, it's too fine for most cutting.

We sell Mirka Polarshine which is a great cutting compound. T10 is our best seller because it can be used on its own, or you can go for a C20 (Coarse 20) and then an F05 (Fine 05). Other brands are Kovax Modente paste or Faracla Profile, both of which are excellent too.

Or would it just be better for the finished result to get it painted in 2 pack polyurethane paint?

Two-pack paint is great for a pattern surface but if you've got a polyester gelcoat surfaces pattern and you're using Unimould to make your moulds (which is a vinylester gelcoat) then there's no need to change to a paint finish. Polyester polishes up really well so I'd just polish up the polyester mould, clean it off, release prep it and pull your moulds!

Lastly, I'm still up in the air about how many layers of reinforcement to use.

I'd say probably two layers of carbon either side of the coremat but if you're in doubt I think it would be a good idea to make up a 'token' (a test sample) that you could bent and break to destruction so that you can know with confidence what layup is right. Start with 2 carbon either side of the coremat and just lay up a small sample. Cure it off and see how it feels. It's a good way to test out your other methods as well and ensure everything is right before the main event.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Cheers MAtt that's really helpful. I've ordered the polish and a few other bits.  I managed to get the plug to a reasonable standard with 1500 and lots of (mould release) wax coats and polish. The mould will need some work but it shouldn't be drastic. My only problem so far has been the pot (both coupling and reinforment resins) exotherming even with the % MEKP being right at the low end and I've only just been quick enough to get the layers on. I'm doing it in the garage without heating, the temperature is around 20 degrees I'd guess.

I have the fast hardener for the laminating resin so I may put the resin itself in the fridge for half an hour before mixing to try to increase the pot life .

I also suspect that the coremat is going to make the part too stiff but I'll make one of each and go from there.