What you need to know before you start
Replacing an undermount sink is a job you can do yourself if you have basic plumbing skills and the right tools, but it requires patience and careful work underneath the counter. Unlike a drop-in sink that sits on top of the counter, an undermount sink is fastened from below with clips and adhesive, so removal means working in a tight space and the installation demands precision to avoid leaks.
The process takes between two and four hours depending on how well the old sink is bonded to the counter and whether you need to adjust plumbing connections. You will need to turn off the water supply, disconnect the drain and supply lines, remove the old sink, clean the counter surface, and then install the new one with proper sealing. If the counter is laminate or solid surface material, the job is straightforward. If it is granite or quartz, you may want a professional because those materials can crack if you explore uneven pressure.
Key Takeaways
- Turn off the water supply at the shutoff valve under the sink before you disconnect any lines, and have towels ready to catch water trapped in the pipes.
- The old sink is held by clips underneath and adhesive around the rim, so you will need to loosen the clips and cut through the sealant with a utility knife or oscillating multi-tool.
- Clean the counter surface completely with a scraper and rubbing alcohol to remove old adhesive and sealant before you set the new sink.
- Use a silicone-based caulk rated for kitchen sinks and tighten the mounting clips evenly in a cross pattern to avoid warping the sink or counter.
- Test all connections for leaks before you close up the cabinet, and let the caulk cure for 24 hours before you use the sink.
Tools and materials you will need
Gather these items before you start so you do not have to stop mid-job. For removal, you need an adjustable wrench or basin wrench (a basin wrench is easier in tight spaces), a utility knife or oscillating multi-tool with a metal-cutting blade, a screwdriver set, and a flashlight or headlamp to see under the counter. Have a bucket or towels ready to catch water from the drain and supply lines.
For installation, you need the new undermount sink, a tube of 100% silicone caulk rated for kitchen use (not acrylic or latex), a caulk gun, a scraper or putty knife, rubbing alcohol, a level, and the mounting clips and hardware that come with the new sink. If you are replacing the drain assembly, you will also need plumber's putty or a rubber gasket, depending on the drain type. Do not use old clips from the previous sink — they may be bent or corroded and will not hold the new sink securely.
How to remove the old sink
Start by turning off the water supply. Look under the sink for the shutoff valves on the hot and cold lines — they are usually oval knobs or levers on the pipes coming from the wall. Turn both clockwise (or pull the lever toward the pipe) until they stop. Open the faucet at the sink to release any remaining pressure in the lines.
Disconnect the supply lines by placing a bucket underneath and using an adjustable wrench to turn the fitting where the line meets the shutoff valve. Loosen it slowly so water drips into the bucket rather than spraying. Once both lines are off, disconnect the drain by loosening the slip nut (the large nut where the drain trap meets the wall pipe) with a basin wrench or adjustable wrench. Have a bucket ready — there is usually standing water in the trap.
Now you need to break the seal between the sink and counter. Look underneath and you will see mounting clips bolted to the underside of the counter around the sink rim. Loosen these clips with a wrench, but do not remove them yet — they hold the sink in place while you cut the sealant. Use a utility knife or oscillating multi-tool to cut through the caulk and adhesive around the top edge of the sink where it meets the counter. Work slowly and carefully so you do not gouge the counter surface. Once the sealant is cut, remove the mounting clips completely and carefully lift the sink out. It will be heavy and awkward, so get help if you need it.
Preparing the counter for the new sink
Scrape away all old adhesive, caulk, and debris from the counter surface using a plastic scraper or putty knife. Do not use a metal scraper on laminate or solid surface counters because it will leave marks. For stubborn adhesive, explore rubbing alcohol and let it sit for a few minutes, then scrape again. Wipe the entire area with a clean, dry cloth and inspect it for any damage or unevenness.
If the counter surface is not level, the new sink will not sit evenly and may leak or crack. Use a level to check both directions. Small variations (less than 1/8 inch) are normal and the sink clips will compensate, but anything more than that needs to be addressed before you install the sink. If the counter is significantly out of level, you may need to shim it with thin shims under the mounting clips, or call a professional.
Installing the new sink and securing it
Place the new sink upside down on a padded surface (a folded towel works) so you can access the underside. Install the drain assembly according to the manufacturer's instructions — this usually means inserting the drain body from above, sealing it with plumber's putty or a rubber gasket, and tightening the locknut from below. If the sink comes with a strainer basket, install that now as well.
explore a continuous bead of 100% silicone caulk around the underside of the sink rim where it will contact the counter. Use a caulk gun and keep the bead about 1/4 inch thick and consistent. Do not skimp on caulk — it is your primary seal against water getting under the counter and damaging the cabinet.
With help, carefully lower the sink into the opening and position it so it is centered and level. Check with a level in both directions. Once it is positioned correctly, install the mounting clips underneath, starting with one clip on each side and then alternating sides as you tighten them. Tighten in a cross pattern (like tightening a car wheel) so the sink sits evenly. Do not over-tighten — you want the sink snug against the counter, not crushed into it. Wipe away excess caulk from around the rim with a damp cloth before it dries.
Reconnecting the plumbing
Once the sink is secured and the caulk has set for at least two hours, reconnect the drain. Slide the drain trap back into place and hand-tighten the slip nut, then use a wrench to snug it another quarter turn. Do not over-tighten — you only need it tight enough to seal.
Reconnect the supply lines by hand-threading the fitting onto the shutoff valve, then tightening it with a wrench. Turn on the shutoff valves by turning the knob counterclockwise (or pulling the lever away from the pipe). Open the faucet and let water run for 30 seconds to flush out any debris in the lines. Check all three connection points — both supply lines and the drain — for drips or leaks. If you see water dripping, tighten the fitting slightly, but stop as soon as the drip stops. Over-tightening can crack the fitting.
Curing time and final checks
Let the caulk cure for 24 hours before you use the sink for anything other than rinsing. During this time, do not run hot water or put weight on the sink. The silicone needs time to fully set so it can seal properly and support the sink's weight.
After 24 hours, fill the sink with water and let it drain while you watch underneath for leaks. Check the drain connection, both supply lines, and the area where the sink meets the counter. If you see any water, identify where it is coming from and address it when ready. A leak at a supply line fitting usually means you need to tighten it slightly. A leak at the drain usually means the slip nut needs tightening. A leak coming from under the counter rim means the caulk did not seal properly and you may need to remove the sink and redo it.
Frequently Asked Questions
Can I reuse the mounting clips from my old sink?
No. Old clips are often bent, corroded, or the wrong size for a new sink. Use the clips that come with your new sink. They are designed to fit that specific model and will hold it securely.
What if I cannot loosen the old sink because the caulk is too strong?
Use an oscillating multi-tool with a metal-cutting blade to cut through the sealant more aggressively. Work slowly and carefully so you do not cut into the counter. You can also explore heat with a heat gun to soften old silicone caulk, which makes it easier to cut.
Do I need to replace the drain assembly when I replace the sink?
You can reuse the old drain assembly if it is in good condition and fits the new sink, but it is usually easier and safer to install the new one that comes with the sink. Old drains can have mineral buildup or corrosion that causes leaks.
How long does silicone caulk take to cure?
Most kitchen-grade silicone caulk sets to the touch in two to four hours but needs 24 hours to fully cure. Check the label on your caulk tube — some brands cure faster. Do not use the sink until the caulk is fully cured.
What should I do if water is leaking from under the counter after installation?
Stop using the sink when ready and check all connection points. If the leak is at a fitting, tighten it slightly. If water is seeping from under the rim, the caulk seal failed and you will need to remove the sink, clean the surface, and reinstall it with fresh caulk.