Things You'll Need
Fast-drying epoxy (optional)
Sink extension pipe
Installing a Kohler cast iron undermount sink to your newly installed granite countertop does not require the assistance of a professional installer. Because there are many different styles and shapes for kitchen sinks on the market, the manufacturer of your countertop will ask you what type of sink you plan to use. When the manufacturer makes your countertop, they cut the hole in the countertop to fit the style of sink. They also drill and install threaded inserts under the counter to help you attach the sink's mounting brackets. Your biggest concern is to take steps to ensure the sink does not leak.
Place a bead of 100 percent silicone caulk around the top edge of the sink, center the undermount sink under the hole in the countertop and then press the sink up against the bottom of the granite countertop.
Place a 2-by-4-inch board across the top of the opening in the countertop and secure a bar clamp through the hole in the bottom of the sink to the board. This holds the sink in place while the silicone dries and while you attach the brackets.
Secure the sink to the underside of the countertop with the supplied mounting brackets. In most cases, you need a screwdriver to thread the screws into the inserts on the bottom of the countertop.
Remove the bar clamp and the board from the countertop.
Place a bead of plumber's putty around the opening in the bottom of the sink and then tighten the sink strainer into place with a pipe wrench. Remove excess plumber's putty with a wet rag.
Slide the extension pipe onto the downpipe extending from the strainer and then slide the other end of the pipe into the trap. Tighten the compression nut on the extension pipe and trap by hand.