Prepare the vapor barrier or underlayment for the butcher block. While butcher block needs this barrier between it and the cabinetry top to avoid wood rot, it also needs to breathe. Cut three to four small holes that are approximately 3 to 4 inches across into the barrier.
Lay the vapor barrier or underlayment on top of the plywood and attach it with a staple gun. Make sure there are no wrinkles in the fabric and that it is tightly attached to the plywood.
Lay the butcher block on top of the counter. You may need a friend to help you position the block -- they are quite heavy.
Screw down the butcher block from underneath with a cordless screwdriver and screws. Choose screws that will penetrate the block without breaking through it. For example, if the butcher block is 3 inches thick, use 2-inch screws. Deduct at least 1 inch from the thickness of the block to help you decide what length of screws to use. Attach one screw every 6 to 8 inches along the frame, working from the underside.