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GusD said..
so am used to working with polyester resin
Epoxy resin is quite the same as polyester, but differ on some points:
- The mix ratio must be exact. With polyester, different mix ratio just slow or fasten the curing time. With epoxy, only the exact mix ratio will cure, the excess in one component will just stay encased in the resin, weakening it
- Curing time is thus less manageable, and exothermia is always a risk
- Epoxy doesnt wet as much the glass as polyester, so if you are used to "pull" resin a lot from the glass, you will leave pinholes with epoxy. In general bubbling during repairs is more a problem with epoxy
- Polyester is harder, so is easier to sand. Epoxy stays softer (which makes it more resilient than polyester, less brittle), and softens with the heat of the sanding. You will have to move about more when sanding epoxy to avoid heat to build up in one place
On the quantities, in my experience, the shelf life of a quality epoxy resin once opened is huge (many years), and you can find it in 1 kg kit. Whereas cheap ones (such as the ones found in the hardware stores) are unusable after some months once opened.