@farmerman,
Ive lately made my own treated pastel surfaces. This I got from a few months of really screwing the mix up and from my above post getting me started.
Fmans Pastel Ground
Get some polishing pumice(its about 600) (I got mine from a mineral supply house at about 2.50 a lb-its pretty light)
Mix equal amount of the pumice with an acrylic gesso paste
Add about 2 T of water and mix it till it gets like smoot buttermilk.
SPread thinly on Bristol or clay board (roughen em up with some 200 grit sandpaper).
I make about 4 coats of thin mix with a light sanding between coats.
When done its a great ground for pastels.
I also add pigments to set up a base color for landscapes and still lifes.
Im sharing this because It was a problem solving thing that I wanted to get over. I think that prices of pastel boards are outrageous.
When I sand, I use and orbital sander with finer and finer grit pads until Im using about an 800 surfacer