After covering studs with cement board we did a trial stack of the single vertical run of glass blocks we were installing. They seemed to fit. After sealing the adjacent wallboard and the seams of the cement board, now some of the blocks won't go in the frame anymore. I have been trying to file back the seams and the board for a few hours and not making any progress. Any ideas how to fine tune my cement board and shave it back so the blocks will fit again? I'm not sure the file method is working. Thanks!