Why do you want to thin it? I found that if you heat it the viscocity drops drastically, but so does pot life. That may or may not be a problem.
Very warm runny resin is a great way to seal a surface. It soaks into anything porous and you can soak or squeegy off the excess to avoid packing on the weight. The resulting surface is very well sealed.
West recommends warming the surface that you're applying the resin to, instead of thinning the resin. This helps the resin flow better when its applied.
Your Doris's old hair dryer is perfect to waft over the epoxy. Don't forget - once you have mixed it thoroughly for 2 minutes, pour it onto a paper plate or similar to stop it going off too quickly.
Other hair dryers are available depending on your gender and - er interests.
The hair dryer allows you to heat it quickly and thin it down.
Acetone is an alternative, but you get terrible amine blush with it - not good.
Shouldn't be too big an issue with the WEST stuff. My highlight.
From their literature -
Amine blush forms as a result of the curing process.
1.1. Blush is water soluble. Remove with water. See Special Preparation?Cured Epoxy page 28 of the WEST SYSTEM User Manual.
And way much less of a problem in Arizona vs. Yorkshire.
1 I'd suggest you contact West and get the info direct from them,
1-866-937-8797
2 In the EZ community, alcohol is suggested by some if you must thin it, never tried it myself.
3 Ditto on the heat. If your having issues wetting out the glass I'd first look at your shop temps, and keep things at room temp or better for several hours before attempting a layup.
A hair dryer is your friend if you need to help it along.
Tim Andres
Thinning is wrong as a soup sandwich. If you actually need a low viscosity epoxy, just buy one.
West is in the 700~800 cps range. I've used a lot of System Three's Clear Coat to seal wood wing skins and fiberglass. At 400 cps it seems like water compared to West. There are epoxies available as low as 200 cps.