Hi, I have been asked to make an item in carbon but the guy already has the mould. However, the mould is made from polyester so how can i protect his mould?

My moulds are polyester gelcoat with vinilester tooling resin from unimould system of ec.

I use 8 layers of easylease and 2x wax on top on the first pull.   Then i just wax it every pull.

Im using epoxy resin to make my parts.

Modern release systems have somewhat alleviated this issue, as they treat both the physical and the chemical bonding sites of the mould surface. Older systems like wax only treat the physical bonding sites, which is why chemical incompatibilities used to be such a big thing because you could still get chemical cross-linking. 

So in most cases, polyester mould surfaces will be fine with epoxy as long as you are using a good chemical mould release system (ideally with a sealer as well). Still considered somewhat risky, which is why you won't get suppliers telling you its fine. If in any doubt, do a test before pulling the trigger. If still in any doubt, spray PVA release agent to prevent any issues and just refinish the part.