I'm laying 6x6 1/4" thick tile for the majority of my tub. Halfway up
though, I'm putting a 3" high strip of 1/8" thick glass tile inlay
around the interior of the tub. This is the type of tile that comes on
the 1'x1' sheets and each tile is 1" sq.

Because I have to build up the thinset to get it to level with the 6x6,
i'm having problems getting the glass tile to set-in without moving
around. I'd like to cut a 3" strip of backboard and put it behind the
glass, but I can't find one thin enough.

Any ideas?

Thanks,
D