Currently working on fibreglass repairs (cosmetic) a on Top Hat 25 (year 1982) and my local fibreglass supplier has recommended Vinyl ester resin base products. Reason being given vinyl ester is the best product to use on old fibreglass as it is compatible with all types of fibreglass resins. Reading other comments in this forum it appears opinions vary. Is vinyl ester compatible with all types of fibreglass materials?
Generally I prefer epoxy as it's compatible with all poly resins and a very simple set formula to mix. Easy to get correct. Never change the mix ratios though as this will weaken the result. Better to change the compound to a fast set kit instead (as opposed to simply adding more catalyst in a poly resin). I've been going marine repairs for years and work on fibreglass wind turbine blades for a living and it's all I use unless an engineer has a sulk about something.
Epoxy also bonds better to vinyl or poly resins that are cured. I prefer to run an angle grinder over the surface lightly to rough up when cured but if not used to doing that then 40 grit would suffice. Just more elbow grease required.
Just use epoxy. It's cheaper because there is less waste. Also the working time is a lot longer so there is no rush.
I've only ever used epoxy on my previous Top Hats, no bonding issues what so ever on everything from filling small screw holes in the cabin top to removing seacocks.
