Could someone explain to me the differences between gel coats and coating resins ?

Hi Ben,

The differences between the two are subtle I guess and are as much to do with individual company's naming proceedures as anything else so I'll only speak for what the differences are between a coating resin and a gelcoat in terms of our range (although this certainly applies to many other resin suppliers that come to mind).

In our range, a Coating Resin is a resin that can be applied onto the surface of a part and will go on without problems of fish-eying away from the material underneath. It can then also be applied over itself again without fish-eying or losing clarity. This might sound quite simple but it doesn't apply to many epoxies and so in general, the ones that it does apply to can be described as coating resins. Coating resins will often have higher viscosities (which helps them with not fish-eying) and also the tend to be quite pure in terms of their chemistry; free from wetting agents, accellerators and viscosity modifiers that can 'blush' to the surface when epoxies are painted onto the surface of a part rather than being used against a moulds surface (and therefore away from air contact). We have only one resin that we sell for such a purpose; our Epoxy Coating Resin.

Gelcoats are generally designed to be applied, on their own, directly to the surface of a mould. They can be filled (almost always the case with tooling gelcoats) or unfilled (as with all clear gelcoats). The purpose of a gelcoat is to provide a solid, unbroken resin layer which sits between the reinforced laminate and the surface of the part creating a smooth, shiny and often protective layer on the part. Gelcoats necessarily have thixotropic additives (often fumed silica but sometimes other additives) which make them thick and allow them to be applied onto a mould's release coated surface without fish-eying.

Either a gelcoat or a coating resin could be used in your application though whether a coating resin would go down onto a release coated mould-surface without fish-eying rather depends on how repellent the release agent is. PVA would probably be fine (but would leave your parts with visible swirls on the surface that would need polishing out), mould release wax might be OK but chemical release agent might be so repellent (so slippy) that the coating resin would fish-eye away.

In either case, you should be experimenting with applying the gelcoat (or coating resin) to the mould first and allowing that to tack-off nicely before adding your main laminate and then pressing it all together. This will ensure that the 'coating layer' can remain in tact, rather than have reinforcement push through it and to the mould's surface.

I suspect GC50 would give you the best results used in this way. It's a nice flexible gelcoat which bonds incredibly well to epoxy and affords a good level of UV protection at the same time.

I hope this helps.

Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales