Undermount kitchen sinks have a sleek configuration that can showcase a countertop and make cleaning easier. They can also be more challenging to install than drop-in sinks. This guide reviews how to install an undermount sink as well as the different types of installation.
What is an Undermount Sink?
- An undermount sink, as the name suggests, is a sink that is mounted underneath a countertop in a kitchen or other room. Drop-in sinks are mounted to the top of the counter top.
- The “hidden” edge of the undermount sink has an attractive, streamlined appearance, and the lack of crevice or a lip makes the edges less likely to catch dirt.
- Popular materials for undermount sinks include stainless steel, cast iron and copper, and they can come in single-bowl and double-bowl varieties.
- Undermount sinks are recommended for granite, solid surface and quartz countertops, but may not be as effective with laminate. They can be more expensive than drop-in sinks.
How are Undermount Sinks Attached?
There are three types of undermount sink installation, distinguished by their different “reveal style,” referring to how much of the sink’s rim remains visible once installed.
- Zero reveal ensures that the edge of the countertop is flush with the opening of the sink.
- Positive reveal ensures that some of the sink’s rim is visible past the edge of the countertop.
- Negative reveal conceals the sink’s rim entirely beneath the countertop, so the countertop edge overhangs.
- Generally, sinks with zero reveal are easier to clean than those with positive or negative reveal. Otherwise, choose a reveal style based on personal preference.
Prepare and Cut the Countertop
- Chose the location for the bathroom or kitchen sink installation, which may be dictated by the location of the water supply lines and other plumbing fixtures in the room.
- Measure the hole for the sink. The easiest way is to turn the sink upside down and trace the outline directly on the countertop with a pencil. Some sinks include cardboard templates, which can be used to trace the sink hole.
- The outline will be slightly larger than the sink’s opening, so make a second outline about 1/2 inches smaller than the original for the hole.
- Cut the hole with a circular saw or jigsaw while wearing safety goggles and work gloves.
- Use a power drill if additional holes for the faucet and other accessories are needed.
- Clean the sink and countertop with denatured alcohol.
Tip: Given the expense of granite countertops and those made of other materials, as well as the risks of causing damage with improper cuts, strongly consider hiring a professional to cut the hole.
Installing an Undermount Sink to an Unattached Countertop
There are two methods to installing an undermount sink. It's easier to install the sink to a countertop before the countertop is attached to the base cabinets. This is particularly useful when attaching a sink with a garbage disposal. You will probably need an additional person to help you turn the countertop.
- Confirm clearance on all sides under the countertop before installing the sink.
- Flip the countertop so the underside is facing up.
- Center the sink over the hole and trace an outline.
- Position sink mounting clips at each corner and at 10-inch intervals along the sides.
- Use construction adhesive to glue the sink clip studs in place. Follow instructions for drying time.
- Using a caulk gun, apply a thick bead of silicone caulk to the countertop along the inner edge of the outline.
- Place the sink down and clip it to the countertop by twisting the wingnuts that come with the clips.
- Wipe up excess caulk with a rag and denatured alcohol. Allow remaining caulk to dry for 24 hours or to manufacturer’s instructions.
- Turn countertop over and finish installation. Attach faucet fittings, garbage disposal and water supply lines as needed.
Tip: If possible, take this approach when considering how to install an undermount sink to quartz countertops.
Installing an Undermount Sink from Under an Attached Countertop
- When replacing or re-installing a sink, begin by shutting off the water supply, disconnecting all faucet and pipe fittings and removing the old sink. Disconnect the garbage disposal.
- Detach any old sink brackets and remove old epoxy with adhesive remover and a scraper.
- Install sink clips to the underside of the counter as needed.
- Set up boards (such as 2- x 4-inch boards) underneath the countertop as a stand for the sink.
- Use a caulk gun to apply a thick bead of caulk around the edge of the countertop.
- Raise the sink so it presses against the underside of the countertop and forms a watertight seal. Add boards and shims as needed to ensure the sink stays in place.
- Use the sink clips to attach the sink to the counter.
- Wipe up all excess silicone sealant you can reach with a rag and denatured alcohol. Allow remaining caulk to dry for 24 hours or to manufacturer’s instructions.
- Remove shims and boards.
- Reconnect faucet, drain, pipe fittings and garbage disposal and turn on water supply.
Learning how to install an undermount kitchen sink has challenges, but following directions when placing these types of sinks can ensure your room has a stylish look. Consider The Home Depot's installation services for projects involving undermount sinks in your kitchen or bathroom.