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TogaMan - 9/25/2020 6:57:38 PM

Hey composite peeps! I am trying out various approaches to gel coat and trying to avoid Polystyrene (though I do work with it). I have been messing with laminating epoxy mixed with black casting pigment with a PVA release. In other applications I use MANN release (more for casting) with excellent release and desired satin finish. (I should mention that I make specialized musical instruments which are a cross between guitar and viola). Generally I make them out of wood but am going over to hybrid CF & or Flax/Hemp with wood veneer in vacuum forms. I have had good results so far with my other parts molds. The neck section required a tricky lay up and I am using the gel coat as a pre-finish black look to bury the otherwise funky CF layup. I was hoping to use a water base polyurethane but that may not go well with some mold release agents without fish-eye. I have considered PVA but have concerns of the water in the urethane dissolving the PVA and either not releasing properly or. integrating into the finish itself. I am aware of some epoxy based upcycled gel coats and have been experimenting with Enthropy upcycled resin (with great results for other applications). Basically, I am looking for ease of repetitive application absent the hassles/odor of polystyrene. The idea is for an ample gel coat (preferably not so nasty stuff) followed by a wet vacuum layup (infusion doable as well) . followed by a urethane foam core. I am making the initial proof part with throw away bagging but generally make silicone vacuum bags for repeated use. Today, I am giving it a go with PVA/black epoxy. I would prefer an easy spray/release finish that won't fish eye (preferably not nasty stuff) as babysitting gravity and epoxy will get old   Any ideas? Thanks in advance!

Jonathan

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Hanaldo - 9/26/2020 1:40:51 AM

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TogaMan - 9/25/2020 6:57:38 PM

Hey composite peeps! I am trying out various approaches to gel coat and trying to avoid Polystyrene (though I do work with it). I have been messing with laminating epoxy mixed with black casting pigment with a PVA release. In other applications I use MANN release (more for casting) with excellent release and desired satin finish. (I should mention that I make specialized musical instruments which are a cross between guitar and viola). Generally I make them out of wood but am going over to hybrid CF & or Flax/Hemp with wood veneer in vacuum forms. I have had good results so far with my other parts molds. The neck section required a tricky lay up and I am using the gel coat as a pre-finish black look to bury the otherwise funky CF layup. I was hoping to use a water base polyurethane but that may not go well with some mold release agents without fish-eye. I have considered PVA but have concerns of the water in the urethane dissolving the PVA and either not releasing properly or. integrating into the finish itself. I am aware of some epoxy based upcycled gel coats and have been experimenting with Enthropy upcycled resin (with great results for other applications). Basically, I am looking for ease of repetitive application absent the hassles/odor of polystyrene. The idea is for an ample gel coat (preferably not so nasty stuff) followed by a wet vacuum layup (infusion doable as well) . followed by a urethane foam core. I am making the initial proof part with throw away bagging but generally make silicone vacuum bags for repeated use. Today, I am giving it a go with PVA/black epoxy. I would prefer an easy spray/release finish that won't fish eye (preferably not nasty stuff) as babysitting gravity and epoxy will get old   Any ideas? Thanks in advance!

Jonathan

I presume you mean polyester rather than polystyrene? Why not try an epoxy gelcoat?

The issue you are going to have, and you've already experienced it, is that epoxies are not thixotropic like polyesters are. So to use a laminating epoxy, you either have to continually brush it until it starts to gel, or you need to modify it with a thixo additive like fumed silica. But fumed silica will make the resin opaque, and mixed with a black pigment the best you will achieve is a dark grey. You could then try to use another filler like graphite powder to get the colour back, but this then won't be a straight black it will be a graphite black with a sort of metallic sheen, somewhat like carbon.

You can get epoxy gelcoats off the shelf though, so these will probably be your best bet.