An undercounter sink's design allows its lip to mount to the bottom of a countertop instead of resting on the counter's surface. This leaves only the sink's basin and wastebasket showing. An undercounter sink can mount to countertops made of any type of material, including granite or other types of stone. All the undercounter sink's sealant, epoxy and mounting brackets are hidden from view. A properly-installed undercounter sink maintains the same structural integrity and load-bearing capabilities as a sink positioned on top.
Position the countertop so its finished surface lies on a solid surface. The underneath side should face up.
Lay the undercounter sink manufacturer-supplied template on the underneath side of the countertop. The template gives the mounting bracket positions.
Drill pilot holes into the countertop, using the template as a guide. Follow the undercounter sink manufacturer-recommended hole size and depth, as stated on the template. The size and depth of the holes depend on the countertop material. Often, stone countertops require 3/8-inch wide and 1/2-inch deep holes for each mounting bracket. Wood or particle board countertops usually need 1/8-inch wide and 3/8-inch deep holes.
Set the mounting bracket studs in a stone countertop. Fill the pilot holes with an epoxy and press the studs into the holes with the threaded ends showing. Give the epoxy 24 hours to dry before continuing. Skip this step when installing an undercounter sink on a wood or particle board countertop.
Clean the bottom of the countertop around the undercounter sink's hole with a rag. If a rag will not remove the debris, then scrape the bottom of the countertop with a putty knife before wiping it with a rag.
Apply a continuous bead of silicone to the undercounter sink's mounting lip.
Position the undercounter sink over its hole in the countertop. Press the sink onto the countertop.
Install the mounting brackets. Place the mounting brackets over the stone countertop's studs and tighten the mounting bracket's nuts with an adjustable wrench. Place the mounting brackets and its screws into a wood or particle board countertop's pilot holes, then tighten the screws with the correct type of screwdriver.