Seriously. That ish makes great basing material and it's dirt cheap. Better you spend the 6 bucks at Home Depot than go steal it from a playground. No need to get arrested cause you're hanging around a kids' playground without a kid :p
So the pic above is an example of what my basing scheme will be for my small Cygnar force (although I reserve the right expand it in the future), in addition to showing the start of my work on Stryker. I'm really like the tan color for his cloak/robe thingy. Anyways, even though my 2 little tubs of GW basing material have lasted me for 4 years, I'm never buying them again. One last thing, if you're trying to do cobblestone or any kind of brickwork with GS, let it sit for at least 10 minutes before you start sculpting in it. My impatience always wins out, and now I have to go back and redo the GS on the medium base there.