Bill, The only model I've done it on was this Tamiya T34. Mainly because if I screwed it up I wouldn't have much invested in it.
The wooden looking thing in the previous post was done pretty much the same. I took a piece of styrene and scribed in some grooves for boards and some wood grain. I brush painted it in various acrylic browns and a bit of dark gray. I helped speed up the drying by using a hairdryer.
Then I sprayed on some hairspray, TRESemme, with a couple of coats drying each in between with the hairdryer.
I airbrushed on some Tamiya Medium Blue and let that dry about 15 minutes.
Brush on some water on the surface and let that sit a bit then use a short bristle brush and go to work. Sometimes it comes off in bigger chunks.
You just got to play around with it some. A lot of it depends on how thick the hairspray coat is and how much paint you put on. I don't remember for sure but I don't think it took much more than an hour to do the whole process from start to finish on this little project. Hans is a figure I picked up that was in a blister pack already painted up. I used to put him in all my WIPs just for fun.
I'm really thinking about trying to do the hairspray whitewash on my Sturm I'm working on. Like I said, I've only done it on the T34 above.