Blushing is only a problem if the surface is directly exposes to air (carbon dioxide & moisture). If the part is made in a mold the exterior surface isn't exposed to the atomosphere. If the part is fabricated using some kind of assistance (vacuum bag, bladder, press) then the inside won't blush either. When making a mold, the only surface that is exposed to carbon dioxide and humidity is the back of the mold. If you're doing laminating over open structures then the blushing could be an issue if your environement very humid.

I haven't used West Systems for the last 10 years and have never used JGreer so I can't comment on those. I don't use WS because of it's rather low HDT (Head Deflections Temp) and Tg (Glass Transition Temp). The HDT of USC 635 is better than WS but isn't quite as good as Proset. When is comes to the physical properties, USC is very good compared to other budget resins. I use MGS for all my part fabrication which is a very premium resin that is suitable for full sized aircraft construction. Here is a link of my comparison of US Composites, Resin Research, MAS against MGS: Epoxy Comparison. You can jump to this page for the final room temp cure after 7 days. HERE are the results after a 125*F post-cure (done after the 7 day room temp cure). The downside to USC is that it's a little more difficult to use than some premium resins due to its higher viscosity.


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