Mounting an Undermount Sink
An undermount sink offers a clean look, with no grout line visible between the sink and the counter. When cleaning food debris off the counter surrounding the sink, you can simply push the debris straight over the edge of the sink cutout, instead of having to gather the debris up in your hands.
Undermount sinks seemingly defy gravity as they sit against the underside of a counter, instead of hanging through the cutout hole from the top of the counter like other sinks. Because of the positioning of an undermount sink, they do need some extra help to cheat the gravitational pull that threatens to cause them to tumble into the cabinet below. This is especially true when the sink is loaded full of water and dirty dishes waiting to be washed.
If an undermount sink is properly installed, it will never separate from the counter. Rushed installation jobs, though, result in the sink separating from the counter within a year or two after the installation has been completed.
The first point sink installers might rush is properly cleaning the counter before starting the installation. This is especially important when working with stone countertops, such as granite. When the countertop installer cuts the sink hole, often the dust from the cutting gathers on the underside of the counter. Wiping the underside of the counter thoroughly with a microfiber cloth clean off the debris, and does not leave behind lint that can affect the sink’s adhesion to the counter.
A sink installer must use waterproof caulk around the top edge of the sink, such as kitchen and bathroom silicone caulk, to create a seal that does not break down when exposed to moisture. The caulk needs to be applied evenly to the sink, since areas of no coverage will cause that portion of the sink to sag.
Once the sink is pushed up against the underside of the counter and is lined up with the cutout, it must be held stationary. This can be achieved by placing a two-by-four board width-wise across the cutout. Bar clamps then must be slid through the drain openings in the sink, with one clamp against the underside of the sink and the other clamp against the topside of the board. The clamps then must be tightened all the way, holding the sink stationary.
An undermount sink should come with mounting hardware, which helps further hold the sink against the counter. If the sink did not come with hardware, check with the sink’s manufacturer or contact the business that installed the counter. Most installation hardware consists of metal bolts and clips. The sink installer must drill holes at the corners of the sink on the underside of the counter, where the bolts will be placed. A two-part epoxy that is waterproof is then mixed by the installer and placed on the ends of the bolts. The installer then inserts the bolts into the holes and slides the clips over the edges of the sink.
The sink, epoxy and especially the caulk must be left alone for a full twenty-four hours. This means the wood and clamps must stay put, and nobody should attempt to install the faucet or any other parts onto the sink. Without the proper cure time, the caulk will not adhere all the way to the sink or counter, causing separation later.