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A popular choice in both bathroom and kitchen designs, an undermount sink is mounted below the countertop for a continuous flow from the countertop into the basin. This type of sink not only offers a distinct, seamless look, but creates uninterrupted counter space and easy maintenance.
If you’ve opted for an undermount sink installation, follow our simple step-by-step instructions to ensure a smooth process. While DIY-friendly, if you’re unfamiliar installing fixtures of this type, we recommend consulting a professional.
Tools & Materials
Pencil
Soft Cloth
Sandpaper
Denatured Alcohol
Silicone Sealant*
Mineral Spirits
*Copper sinks require a Neutral Cure Silicone Sealant
Make sure that the water supply has been shut off and the plumbing fixtures have been disconnected before you begin to install the sink.
Carefully turn the vanity top over so that it rests upside down on a stable, cushioned surface. One of the differences between an undermount sink and a standard drop-in sink is that the cutout must be cut precisely to match the sink dimensions.
Smooth the edges of the hole with sandpaper so it won't damage the sink. Clean the dust from the vanity top and the opening with a clean cloth and denatured alcohol. Be sure to allow the surface material to dry completely after cleaning for the adhesive to be able to work properly.
Position the undermount sink over the cutout on the vanity top. Make sure the sink is centered with the faucet hole and is evenly spaced between the bolt holes. Ensuring it’s correctly aligned is critical before moving to the next step.
Using a pencil, draw an outline of the sink on the vanity top, once the ideal position is determined.
After tracing the outline, remove the sink from the vanity top. With the sink flipped upright, apply a generous bead of silicone to the perimeter of the sink’s rim. Ensure the bead of silicone is a uniform amount all around.
Use denatured alcohol again to clean the edge around the sink hole where the sink will be positioned. This will remove any grime to ensure proper bonding with the silicone.
Carefully place the sink upside down on the vanity top cutout, positioning it within the outline that was previously traced.
Press the sink firmly to ensure the proper spreading of the silicone. The weight of the sink should push against the vanity top, but if it’s very light, consider using a weight or another person to help press it down.
While one person raises the sink up and places it on the vanity top, the second person should make sure it’s positioned properly.
Attach the sink clips (if included) by placing the long end of the bracket flat against the sink lip. Screw the wing bolts through the brackets and bolt holes and tighten snugly.
Before you tighten the sink clips, adjust the position of the sink. You want to do this before the silicone sets, so you have the opportunity to make it align perfectly with the cutout in the vanity top.
After the silicone has fully dried, carefully turn the vanity top and attached sink over. Make sure there aren’t any gaps between the undermount sink and the vanity top. If you notice a gap, the sink clips may not be tight enough.
As you push the sink against the countertop, it may cause some of the silicone to squeeze out. Wipe it up right away to prevent it from hardening. Remove any excess silicone with a cloth moistened with water or mineral spirits. Let the silicone dry according to the manufacturer’s instructions.
You may have to wait for up to 24 hours for adequate drying of the silicone before proceeding to install other fittings, such as the faucet.
An undermount sink is mounted below the countertop, creating a continuous flow from the countertop into the basin.
When installing an undermount sink, a popular method attaches the sink to the countertop before adding to cabinetry for a precise and secure fit. Alternatively, you would need to install your undermount sink before the countertop.
Installing an undermount sink is something most DIYers can do, though it’s a bit more involved than installing drop-in sinks. Cutting the countertop to the sink’s precise measurements is often considered the trickiest part, with the rest fairly straightforward.
An undermount sink can have a positive, negative, or zero reveal. A positive reveal is where the countertop edge sits back from the edge of the sink and a small portion of the sink rim is exposed. A negative reveal is when the countertop extends slightly over the top edge of the sink on all sides. A zero reveal is when the sink and the countertop align perfectly flush on top of each other. These options give you more flexibility to better customize your look.
Undermount sinks are best suited for solid surface countertop materials like granite or marble. They are less suited for laminate or tile countertops, which have too many weak points along seams and grout lines to support the weight of the sink.
Besides its streamlined appearance, homeowners enjoy this style because it makes cleaning much easier than drop-in sinks, for example. Since the edge of the sink is hidden below the vanity top instead of sitting on top of the counter, the lack of a lip makes the edges less likely to catch dirt.
Installing an undermount sink in your bathroom can take 30 minutes or less with the correct tools and materials at hand. If it’s your first time taking on this type of project, it can take longer depending on how many people are assisting. Make sure that the bathroom is not essential when you decide to complete the installation, so there is less foot traffic and interruptions.