Install a Cast Iron Sink

Cut the sink hole out of the countertop using the previously marked line as an indicator. Use the spade bit to drill a hole anywhere on the line to get a starter point where the jigsaw can fit into the indicator and begin cutting without having to break any blades. The most important aspect of this cut is that an area is left for the lip, so the sink hole must accommodate this lip on the edges.

A cast iron sink is much heavier than other drop-in sinks. Extra supports aren't always necessary, but they will prevent any major catastrophe if the structural integrity of the kitchen countertops fails. Measure the depth of the bottom of the sink, and mark this with lines on either side of the cabinets beside the sink hole for side brace placement. The plywood will fit on top of these braces, so account for this extra material. The sink is barely held up by the complete support system so it doesn't lift off the countertop. Measure and mark from the back of the cabinet to the front to give ideal support for the cast iron sink.

Cut the 2-by-4 piece of wood into two support beams for either side of the sink base. Place the sized support on the marked template below the sink hole, and drill a hole through both the 2-by-4 and cabinetry according to these markings. Screw a wood screw to hold up the wood to the template on the cabinet. Repeat this step on the opposite side. Allow the supports to hang freely, and check the level across the two pieces. Once the supports are level, drill three more holes in each. Secure the supports to the cabinets with three more wood screws in each support.

Find measurements for a middle piece between the two support braces. Cut the piece so that it will sit flush with the two support braces. Check the level of the piece across the braces to make sure there's no incline / decline. Drill a diagonal hole into each side of the middle support brace through the side support brace. Screw in a wood screw to brace the middle support to either side.

Measure and mark the plywood so it will fit squarely on the support system. Round down on measurements to make sure the plywood support will fit inside the cabinetry. Cut a hole out of the plywood to give the water lines the best access to the sink. Most sinks will have the sink connect to the water lines either in the center of the sink or in the rear, so cut accordingly. Don't cut directly in the center of the plywood, as this is where the sink needs support. Cut the plywood so it will fit in the cabinetry. Drill matching brace holes in both the plywood and 2-by-4 boards. Screw the plywood cutout into the support system.

Inspect the sink flange to decide if caulk or plumber's putty is the best option to seal the sink. Spread caulk (with the caulk gun) or plumber's putty around the perimeter of the sink hole. The lip of the cast iron sink will sit on the caulk or plumber's putty to secure it to the countertop. This step is time-sensitive because it will begin to dry quickly, so put the sink down soon after placing the caulk or plumber's putty. You'll need help placing the sink in the sink hole evenly. Use the putty knife and rag to clean up any caulk or plumber's putty that seeped out from under the sink lip. Watch our Video: How Do I Use Caulk?

Install the water lines, faucets and drain lines into the cast iron sink through the hole cut in the plywood support. Use the thread sealer on the threads before you screw the lines into the sink or connection lines. Replace any washers with new ones that may have come with the sink.