Hi,

I'm a teacher and work with teenagers and am considering building a kayak with one particular class group. I already have a mould from which one successful polyester/glass boat was pulled about two years ago. The mould is also polyester/glass with a polyester gelcoat. The mould needs some minor modifications to change aspects of the kayak design that have become apparent in the meantime. Basically, I'll need to cut six slots, remove some material and then re-glass up the mould to make it rigid again. The total area of the modifications will be 6 slots each about 1 inch by 3inches. I intend to make the new boat from resin infused epoxy with a mixture of reinforcements including carbon, diolen, glass and kevlar with soric as a core material.

I understand that a polyester mould is risky to be using with epoxy, so my first question is whether the epoxy compatible gelcoat will lessen the chances of the new component sticking to the old mould?

The second question is whether I should use other materials to modify the mould to prevent there being any fresh polyester in contact with the new component? (if so, which materials?)

Third question, what release agent should I use? (the mould has a good finish and was well prepared with release wax previously),

Thanks,

Donnacha.

Hi Donnacha,

Sorry for the delay in getting back to you. Matthieu, thanks for deputising!

I understand that a polyester mould is risky to be using with epoxy, so my first question is whether the epoxy compatible gelcoat will lessen the chances of the new component sticking to the old mould?

Firstly, using the GC50 Epoxy Compatible Gelcoat will get round your problem of releasing an epoxy part from a polyester mould. There is no likelyhood that you will have any release problems if you use the GC50 on your mould, even after making the polyester repairs, when you subsequently lay up the boat using epoxy resin infusion. Put simply; this is a good idea.

The second question is whether I should use other materials to modify the mould to prevent there being any fresh polyester in contact with the new component? (if so, which materials?)

This is a good question but I don't think it will be neccessary to treat these freshly repaired areas differently providing you are using the GC50 gelcoat. The key is always to allow the a new mould (or mould repairs) to cure as fully as you possibly can before using the mould. This might mean putting the mould somewhere warm for a few days (if possible). A good way to check how well cured a mould or repair is is to smell it! - If it still smells quite noticibly of styrene then it's best to hold off with your laminating for a while.

Third question, what release agent should I use? (the mould has a good finish and was well prepared with release wax previously)

Since I don't think you'll have any trouble releasing the GC50 gelled part from the mould, the choice of release agent is totally up to you. You could go with mould release wax again (be sure to thoroughly wax over the repaired area lots of times!) or you could strip the wax off using some mould cleaner and go with a chemical release agent instead. I think either would be fine.

One final tip; for total peace-of-mind you could always check the combination (mould, release agent, gel, epoxy) on a small area to check compatibility before doing the main layup. Although this takes an extra day, it will ensure you don't go through the heartbreak of a sticker should any of the above materials present a suprise incompatibility.

I hope this helps and look forward to working with you.

Best regards, Matt


Matt Statham
Easy Composites / Carbon Mods - Technical Sales