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.

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

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.

Cheers Matt, I'll ring in the week and order the bits.

Hi Mike,

For none-vacuum use coremat will work fine and will add plenty of stiffness to your laminate; its inexpensive and easy to use. If you wanted something higher in performance you could use some closed cell pvc foam - the 3mm is very nice to work with and with a heat gun you can soften it and shape it in advance to follow the contours of your mould but coremat is still fine too.

I don't think I would worry too much about the exposed edge of the coremat for your switch appertures. You could also try to wet out and coat the cut edges with some more epoxy to seal them after you've cut them.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Cheers Dave

First two I make will be standard wet layup with carbon fibre. For stiffness and cost saving I had the idea to use coremat as it won't be under vacuum.  A snag I came across is that there needs to be an aperture for the lights of course, and I dont think coremat can be exposed at the edges ie, the ones I've made so far have been in glass and I've cut out the aperture for the lights.  If I use coremat, I guess I'll have to cut a hole in the coremat first, then leave a decent carbon overlap so as not to expose the edges of the coremat?  Could just do with some layup guidance really to give a stiff but light result without a resin infusion method.

You haven't specified what composite layup you will be replacing the part with/method of creating it but just in case...

Coremat is a lower end core that is used mainly in fiber glass layup. The main draw back is that it is compressible so if you are planning to use say an infusion method or any method that involves putting pressure on the layup then you will need a different core. Some to name are Soric or Closed Cell PVC which EC supply.

Dave.

to clarify, I mean coremat when i say "sandwich"

Thanks Matt.  With it being a fairing, it needs to remain pretty stiff at high speed, do you think two layers of carbon and a sandwich in between would be sufficient? Or more carbon? Its fixed at each edge with bolts so the bolt areas need to be robust as that's what carries the stress at speed.  The first couple I make will just be standard wet layups, not vac'd.  I plan to use peel ply on the back for a decent finish (I've done this before with wet layup to good effect).

Would you also use carbon tape around the edges between the carbon layers or not neccessary? I'm thinking that would give thickness and reinforcement to the bolt areas.

Hi Mike,

I think I'm with Joe on this one. Both systems woudl do the job well but if you're comfortable with slightly more conventional fibreglassing techniques then Uni-Mould would probably be the way to go. If you've not done fibreglassing before then the putty system tends you yield better results in the hands of a first-timer but neither are difficult and I don't think you would have a problem either way.

As for the flanges, again, this is a preference thing. If you did lay the part onto a flat board then you will indeed need a reasonable amount of clay to fill the gap from the part to the board (in places) but the clay is inexpensive and re-usable afterwards. The advantage to this method is that the flanges you're left with are flat which might actually make things even easier when it comes to laying your various bagging consumables etc. You can make them as big as you want (like Joe says, the bigger the better) by laminating plent of material onto the 'board', like a good 150mm. If you do it with signboard then again, make sure you make them plenty big enough. It will be just as easy to do it this way but you'll end up with flanges that come off at different angles which might just be a fraction less easy to lay your consumables down onto.

Both would be fine I'm sure.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales