West system on top of MAS epoxy?

Has any one had a problem coating MAS epoxy with West System epoxy or vice versa? I may run out of MAS but have slow acting West in the shop.


Dave Metcalf

4 replies:

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RE: West system on top of MAS epoxy?

As long as the first coat has fully cured you're guaranteed OK. I think that nemochad once posted that he's had success with less than full cures, but find the post, don't take my word for it.

Note that a full cure means sanding between the coats.

Good luck,




RE: West system on top of MAS epoxy?

   Yep, I frequently do fillets with West and fast hardener, followed by tape or glass wet out with somebody else's resin with slow hardener. I like having the fillet a little firm when laying down pre-wetted tapes, or when wetting glass - the fillets don't get as mushy when the runnier straight resin is applied to the cloth.

If you mix each brand seperately (the epoxy cross-linking occurs in the cup, while mixing), you can then combine the two mixed brands in one cup even. Useful if you want to add some speed to a mix, just mix and add some 5 minute stuff to your already mixed regular brew to get an extra quick kick (and consequent very short pot life, beware).

The resin I buy in the largest quantities is pretty slow- at least 36 hours in my heated but pretty cool shop, so for tasks that don't need as much open time, but do take a large amount of epoxy (so the cost of West in my case, becomes prohibitive), like a batch of fairing putty that I want to sand in the morning, I'll mix my bulk slow epoxy, add thickeners, then mix a little fast stuff, add it to the bulk mix, slightly adjust with thickeners if needed, dispense onto a cardboard palette (more surface area, slower exotherm, but make sure it's thick enough to be truly 'non-sag' first), and apply.

There may be some epoxies out there with fundamentally different chemistries, but nothing I've been able to buy hasn't intermixed just fine. I'm pretty sure the solvent laced epoxy paints, or the single part 'epoxies' are pretty different than our standard resins - don't mix those in.

RE: West system on top of MAS epoxy?

Thanks guys.  


RE: West system on top of MAS epoxy?

   I have used West System over MAS with no apparent problem.  There is usually plenty of cure time in my shop.

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