Measure the length and width of the top of the base cabinets. Add 5/8 inch to the width to allow for the front overhang. Add extra to the length if you want the countertop to extend over the ends of the base cabinets.
Reinforce the walls of the cabinets with 1-by-4-inch lumber. Measure and cut the wood to the depth and width of the cabinets using a circular saw. Attach the lumber on the insides of the cabinet sides and back so the edge of the lumber is flush with the cabinet edge. Use screws to secure the 1-by-4s on inside pieces of cabinetry. For exposed ends of the cabinets, apply carpenter’s glue to the 1-by-4 and hold it in place with wood clamps until it dries.
Cut 3/4-inch exterior-grade plywood to the dimensions you determined in Step 1. Set the plywood pieces on the base cabinets. Check that the plywood is level front to back and side to side using a carpenter’s level. Add wood shims under the plywood and on top of the base cabinets to level the plywood, if necessary.
Secure the plywood to the base cabinets with screws placed approximately 6 inches apart, using 1 5/8-inch screws. To keep the wood from splitting, pre-drill the holes before attaching the screws. Set all screws below the surface.
Cut 1/2-inch cement backer board the same dimensions you cut the plywood. Measure the thickness of a tile. Add the thickness of the plywood and the backer board to tile’s thickness for the depth of the backer board strips you need to cut for the edge of the countertop.
Mix thinset mortar according to package directions. Apply thinset 1/4-inch thick to the top of the plywood, using a notched trowel. Set the backer board on top of the plywood and mortar. Secure the backer board with 1-inch shingle nails placed 6 inches apart along the edges and 8 inches apart across the rest of the countertop area. Set all nails below the surface with a nail set.
Apply a 1/4-inch layer of mortar to the front and side edges of the countertop. Place the backer board strips along the mortar and secure them with 1-inch shingle nails, spaced 6 inches apart. Continue installing the tiles on your raised countertop.