I've never gone the IPA route because plain old water with a drop or two of Dawn in my atomizer works so well. I always pre-wet scenery and ballast before applying Elmer's white glue/water/detergent mixture of "glue" to the scene with a big dosing eyedropper...but, it's important when pre-wetting to have a very fine "atomized" mist, and not big drops raining down on freshly contoured ballast or dirt which will easily crater what you've spent your precious time getting just right, which means that large spray applicators such as old 409 sprayers or the equivalent you can buy brand new, always have much too coarse water droplets and too much velocity. An easy solution is the small spray applicators you can buy for CA "Zip-Kicker"/"Accelerator" at your LHS, which produce a very fine, low-velocity mist.
Cheerio!
Bob Gilmore
