You can install your farmhouse sink 3 different ways...
Your installation options for a farmhouse sink are under-mount, flush-mount, or top-mount. Some sinks are designed specifically for a particular method and some are designed for any method. Check to see which method your sink is designed for before purchasing. Each farmhouse sink installation method comes with its own set of pros and cons:
Under-Mount: The countertop overlaps the edges of the sink so they are hidden.
Pros: It's easy to clean your countertop; just wipe right over the edge and into the sink.
Cons: Requires extra support during installation (not a huge downfall though)
Flush-Mount: The top edges of the sink and the countertop are the same height.
Pros: It's easy to clean your your countertop; just wipe right over the edge and into the sink.
Cons: The silicone sealer between the sink and countertop is visible.
Top-Mount: The top edges of the sink sit higher than the countertop.
Pros: You can decide how high you want to set your sink above your countertop.
Cons: It takes a little extra cleaning around the joints between your sink and countertop.
How To Install A Farmhouse Sink
In order to install a farmhouse sink, you need to have some basic "handyman skills" and a second person to help you lift and position the heavy sink. If you don't, it's best to let a professional do the installation for you.
Basically, you're going to make a platform inside your sink cabinet for your farmhouse sink to rest on since it is too heavy to support itself.
Tools and materials needed: Cut-out template or cardboard, marker, scissors, jigsaw, 2-by-4-inch board, 3/4-inch plywood, table saw, construction adhesive, wood screws, drill.
Note: always follow your sink manufacturer's instructions for installation.
Locate the cut-out template: a cut-out template is included with every farmhouse sink. The cut-out template is a paper or cardboard drawing of the front face of the sink. If you cannot find your template, place a piece of cardboard over the front apron of your sink and trace around the edge with a marker and cut the cardboard.
Remove the false drawer faces or flip-down drawers of your existing sink cabinet: If you have a new apron-ready cabinet, there are no false drawer faces, just a wood panel.
Position your template and cut: Decide what height you want your sink to be at (make sure the bottom of the sink is above the cabinet doors), then place the cut-out template centered on the front of the cabinet and trace the apron face onto the wood above the cabinet doors. If your sink is the same width as your cabinet, you will need to cut the front, sides and back of the cabinet for the sink to fit. Cut around the outline using a jigsaw.
Cut ledge boards for the farmhouse sink: Measure the inside depth (front to back) of the cabinet. Cut two pieces of 2-by-4-inch board to this length using a table saw. Now measure the inside width of the cabinet (side to side) and deduct 4 1/4 inches. Cut one 2-by-4-inch board to this length. Measure the depth of the sink. Calculate the depth of the sink in the cabinet based on the height you want your sink to sit at. Mark the depth of the sink plus 3/4-inch on the inside walls of the cabinet (each side). Use a level to draw a horizontal level line on both sides and the back wall at your mark.
Install farmhouse sink ledge boards: Apply construction adhesive to the back of one of the cut side boards. Set the board against the side wall so that the top of the board touches the line you drew. Screw through the boards into the side of the cabinet using 4 wood screws, evenly spaced. Repeat for the other side and the back pieces.
Cut platform for farmhouse sink to sit on: Measure the inside dimensions of the sink cabinet (width and depth) and deduct 1/4-inch from each measurement. Cut 3/4-inch plywood using to these measurements using a table saw. Set the board on top of the ledge boards you installed earlier and note the location of all the plumbing. Use a marker to draw on the plywood all the openings needed to be cut for plumbing. Cut out the openings. Cut the opening for the sink drain pipe slightly larger than the pipe. Test the fit.
Install the farmhouse sink platform: Apply construction adhesive to the top of the ledge boards. Place the plywood on top and screw through the plywood into the ledge boards with wood screws. Place a screw every eight inches or so. Then follow the manufacturer's instructions to mount the sink to the plywood.
Caulk around the edges of the sink once the countertop and plumbing are fully installed.