If you don't pre-drill when boardiing out there is the POSSIBILITY that when the screw breaks through the board and goes into the substrate it can lift the board up the screw and thus leave a void between the substrate and board.
Pre drilling the BOARD eliminates this possibility if you pre-drill with a drill a fraction larger than the shank size of the screw. The board is then clamped into position wothout any void, thereby giving a guaranteed solid bed.
I know it takes a bit longer, but not as long as going back to the job sometime later to repair broken tiles.
Grumpy |