Can anyone tell me what’s the best thing to skim my mould with. It’s made from epoxy resin and fibre glass but as I never used a gel coat for various reasons it needs a final layer that I can sand and polish to a mirror finish.
I could use normal epoxy resin but that’s going to be a task and a half to sand smooth.
Someone in previous post of mine that I could use pattern coat primer but that’s apparently polyester and won’t bond to well to my mould.
I’m a little stuck with the best thing to use, it’s obviously needs to be durable yet preferably easy to sand smooth, help please?

Duratec surface primer and hi-gloss clear are made for resurfacing moulds, so they would be your best bet.

But in all honestly man, speaking from 10 years of experience - nothing will work like you want it to. Resurfacing a mould is not an easy thing, especially when you have tight recesses like you do. Perhaps your one mould would be ok, the flatter one. But the other one with the deep 'canopy' section, you will never get an even coating on that and if you get a run or a sag or a brush stroke or anything like that then it becomes a physical lock. Given you used rattle cans to paint the moulds, I'm assuming you don't have proper spray equipment to apply any coatings well either? So you are really fighting a losing battle here.

Your best solution is to remake the moulds. You will waste less time and money just starting again. if you don't have the original part you used to make the moulds, then use your current moulds to make a fresh male copy that you can then paint and sand and rework nicely. You will need to find a way to spray PVA release agent in order for that to work though, I would suggest a Preval sprayer if you want something cheap and easy.