Yes, you can replace an undermount kitchen sink yourself, even if you are a beginner DIYer, by following a few clear steps. Replacing an undermount kitchen sink involves careful removal of the old unit, cleaning the space, preparing the new sink, and securely mounting it under the countertop. This guide provides simple, step-by-step instructions to help you complete the job right.
Preparation: Getting Ready for Sink Replacement
Good prep work makes the whole job much smoother. Before you start pulling things apart, gather your tools and protect your kitchen space. This section walks you through the initial setup needed for a successful swap.
Essential Tools and Materials Checklist
You will need a specific set of tools for this job. Having everything handy prevents annoying mid-project searches.
| Tool/Material | Purpose |
|---|---|
| Safety Glasses and Gloves | Protect eyes and hands. |
| Utility Knife or Scraper | To cut old sealant. |
| Pliers or Basin Wrench | To disconnect water lines and drain. |
| Adjustable Wrench | For tightening connections. |
| Screwdriver Set | To remove or adjust mounting clips. |
| Shop Vacuum | To clean up debris and water. |
| New Undermount Sink | The replacement unit. |
| Silicone sealant for undermount sink | For a waterproof seal. |
| Mounting Clips and Hardware | Often come with the new sink. |
| Support Blocks (Wood) | Temporary support during drying. |
| Towels and Buckets | To catch water spills. |
Shutting Off Water and Power
Safety first! You must stop the flow of water before disconnecting any plumbing.
- Locate the Shutoff Valves: Find the hot and cold water valves under the sink.
- Turn Off Water: Turn both valves clockwise until they are fully closed.
- Test the Faucet: Turn on the faucet handles to release any pressure in the lines and confirm the water is off.
- Disconnect Power (If Applicable): If you have a garbage disposal, unplug it from the outlet or turn off the circuit breaker controlling the disposal power.
Step 1: Removing Old Undermount Kitchen Sink
Removing old undermount kitchen sink requires patience, as the old adhesive can be very strong. This is often the hardest part of the whole replacement.
Disconnecting Plumbing Fixtures
You must clear everything attached to the sink bowl before lifting it out.
Disconnecting the Drain and Strainer
- Place a bucket under the P-trap assembly to catch any remaining water.
- Use channel locks or pliers to loosen the slip nuts connecting the P-trap to the tailpiece and the drainpipe coming from the wall.
- Remove the strainer basket assembly. This often involves unscrewing a large locknut from underneath the sink bowl. Take your time; these parts can be stiff.
Disconnecting Faucets and Supply Lines
- Use an adjustable wrench or basin wrench to disconnect the flexible supply lines from the shutoff valves.
- If the faucet is mounted through the countertop (and not the sink rim), you may leave it in place, but check clearance first. If it’s mounted on the sink, disconnect the lines and remove the faucet assembly according to its manual.
Separating the Sink from the Countertop
The sink is held in place by clips and a heavy layer of sealant.
- Cut the Sealant: Use a sharp utility knife or a specialized putty knife to carefully cut through the silicone sealant for undermount sink that runs all the way around the rim where the sink meets the stone or solid surface countertop. Work slowly around the entire perimeter.
- Locate and Remove Clips: Look underneath the counter. You will see securing undermount sink clips screwed into the countertop material and pressing against the sink flange. Use a screwdriver or wrench to loosen and remove every clip. Keep the clip hardware organized; you might reuse some if they fit the new sink.
- Apply Gentle Pressure: Once the clips are off and the sealant is cut, gently push up on the sink bowl from below. It might not move right away. If it’s stuck, try tapping the rim gently with a rubber mallet.
- Remove the Old Sink: Have a helper ready. Slowly lift the old sink down and out of the opening. Undermount sinks are heavy, even when empty. Set the old sink aside carefully.
Step 2: Cleaning and Preparing the Countertop Surface
A clean surface is crucial for a strong, lasting bond. If you skip cleaning, your new sink might not seal properly.
Removing Old Adhesive Residue
- Scrape away any remaining large chunks of old caulk or adhesive using a plastic scraper or putty knife. Be very careful not to scratch the finished surface of your countertop, especially if it is granite or quartz.
- Wipe down the area with mineral spirits or rubbing alcohol. This dissolves the final traces of silicone and grease.
- Ensure the entire mounting surface is completely dry before moving on.
Inspecting the Cutout and Faucet Holes
Check the opening in your countertop. If you are replacing drop-in with undermount sink, you might find the opening is too small or improperly finished for an undermount.
- If you were replacing an old undermount with a new one of the same size, just inspect for damage.
- If you are switching styles or sizes, you may need professional countertop modification, which usually involves specialized tools for cutting stone. This guide assumes you are replacing one undermount sink with another of a similar or standard size that fits the existing hole.
Step 3: Dry Fitting and Prepping the New Sink
Before applying any glue or sealant, test how the new sink fits into the opening.
Testing the Fit
- Lift the new sink into the opening from below.
- Ensure the edges sit flat against the underside of the countertop surface.
- Check that the drain openings align correctly with your existing plumbing rough-in. Make minor adjustments now if needed.
- Remove the sink and set it aside.
Preparing the Sink for Mounting
If your new sink did not come with mounting hardware, you will need new clips. This is where the undermount sink installation guide provided by the manufacturer is most helpful for clip placement.
- Install Clips (Temporarily): Follow the manufacturer’s directions for positioning the mounting clips. Generally, they are spaced evenly around the perimeter. Do not fully tighten them yet; just get them in position. These are the securing undermount sink clips that will hold the weight while the sealant cures.
- Install Strainer and Flange: It is much easier to install the drain flange and strainer assembly onto the new sink before you mount the sink under the counter. Follow the drain manufacturer’s instructions, using plumber’s putty or a gasket as required for a watertight fit.
Step 4: Attaching Sink to Countertop
This is the moment of truth—permanently mounting your new sink. We use two main components here: strong adhesive/sealant and mechanical clips.
Applying the Sealant
The best adhesive for undermount sink applications is high-quality 100% silicone sealant designed for kitchen and bath use. It provides a strong, flexible, and waterproof bond.
- Apply a continuous, thick bead of silicone sealant for undermount sink directly onto the flat lip (flange) of the new sink bowl. Run the bead all the way around the perimeter where it will contact the stone. A generous, even layer is vital for waterproofing.
Raising and Positioning the Sink
- With your helper, carefully lift the sink up into the cutout opening.
- Align the sink so the drain holes are correct and the sink is centered in the opening.
- Gently press the sink flange up against the underside of the countertop.
Securing the Sink with Clips and Brackets
Now you will use the mounting hardware to pull the sink tightly against the countertop surface, ensuring the sealant makes full contact. This process involves attaching sink to countertop securely.
- Engage the Clips: Start with the clips opposite each other (e.g., front-left, then back-right). Use your wrench to tighten the mounting bolts or screws on the how to install sink clips.
- Adjusting Underneath: As you tighten one clip, check the sealant line above to ensure the sink is being pulled up evenly. You want to see a small, consistent squeeze-out of silicone all the way around.
- Adjusting Undermount Sink Brackets: If your sink requires specialized support brackets (common for heavy cast iron or deep sinks), follow the specific instructions for adjusting undermount sink brackets. These brackets often sit on the cabinet base or frame for added vertical support.
- Final Tightening: Work your way around the sink, tightening all clips gradually. Do not over-tighten, especially if you have a thin solid-surface countertop, as this can cause cracking. The goal is firm pressure, not crushing force.
Step 5: Final Plumbing Connections and Curing
The physical installation is done, but the plumbing needs reconnection, and the sealant needs time to set.
Reconnecting the Plumbing
- Check Alignment: Make sure the sink drain assembly lines up perfectly with the P-trap and waste pipe coming out of the wall.
- Connect Tailpieces: Reattach the tailpieces and slip nuts to secure the drain assembly. Hand-tighten first, then use pliers for a quarter-turn more. Do not overtighten plastic fittings.
- Reconnect Supply Lines: Reconnect the hot and cold water supply lines to the faucet stems. Again, tighten firmly but avoid excessive force.
- Garbage Disposal: If applicable, remount the disposal unit according to its instructions and plug it back in or restore power at the breaker.
The Curing Period
This waiting time is non-negotiable for a waterproof installation.
- Sealing Undermount Sink Edges: Wipe away any excess silicone that squeezed out around the perimeter using a damp cloth or a rag dipped in mineral spirits (check the sealant’s instructions first). Aim for a clean line where the counter meets the sink.
- Curing Time: Most silicone sealants require 12 to 24 hours to fully cure before they can handle weight or water exposure. Check your specific sealant product for the exact time needed. Do not run water or place heavy items in the sink during this period.
Step 6: Testing and Final Inspection
Once the sealant has cured, it is time to test your work.
- Test Water Flow: Slowly turn the water shutoff valves back on. Check immediately under the sink for any drips around the supply line connections. Tighten gently if leaks appear.
- Test the Drain: Run water into the sink for several minutes. Check all drain connections underneath again for any signs of leaks around the strainer or P-trap joints.
- Inspect the Seal: Look closely at the sealing undermount sink edges where the silicone meets the counter. The bond should look uniform, clean, and solid.
What If I Need to Replace Drop-in with Undermount Sink?
If you are replacing drop-in with undermount sink, the process is slightly different because drop-in sinks sit on the counter, covering a larger hole.
- Removing the Drop-in: Cut the caulk seal, unscrew the retaining clips underneath, and lift the sink straight up and out.
- Countertop Modification: The opening for a drop-in sink is usually too small or incorrectly shaped for an undermount. You will likely need a professional templating and cutting service to enlarge the hole safely, especially with granite or quartz. This step is complex and often requires specialized diamond tools.
- Installation: Once the counter is properly cut, proceed with Step 3 (Dry Fitting) of this guide.
Guide to Different Sink Mounting Hardware
When you are how to install sink clips, you might encounter different types of hardware depending on your countertop material.
| Countertop Material | Common Clip Type | Special Consideration |
|---|---|---|
| Solid Wood/Butcher Block | Simple metal screws and clips | Screws can go deep; watch for plumbing pipes. |
| Laminate/Solid Surface | Clips requiring longer screws or specialized anchors | Ensure screws don’t poke through the top surface. |
| Granite/Quartz/Marble | Clips often secured with epoxy or specialized anchors | Requires extreme care not to crack the stone during tightening. |
Adjusting undermount sink brackets properly is key for heavy sinks like cast iron or fireclay, as silicone alone cannot handle the static weight over time. These brackets often bear the main structural load.
Frequently Asked Questions (FAQ) About Sink Replacement
Q: Can I reuse the old clips when installing a new sink?
A: Only if the new sink has the exact same mounting points and thickness, and the old clips are not rusted or damaged. It is usually best practice to use the new hardware provided with your sink, as it is designed for that specific model.
Q: What is the difference between plumber’s putty and silicone sealant for sinks?
A: Plumber’s putty is used primarily to seal drain flanges and strainers to the sink bowl itself. It remains soft and pliable. Silicone sealant is used to create the waterproof bond between the sink rim and the countertop material. Silicone cures hard and waterproof, which is essential for supporting the sink’s weight.
Q: How much weight can silicone support under a sink?
A: While silicone provides a strong initial grip, it should not be relied upon as the sole support for a heavy undermount sink (like fireclay or cast iron). The mechanical clips and brackets bear the primary load. Silicone ensures a watertight seal and prevents shifting.
Q: Do I need to remove the garbage disposal to replace the sink?
A: Yes, generally, you must disconnect the garbage disposal and remove it from the old sink’s drain opening before you can lift the old sink out. Reinstall it onto the new sink’s drain assembly afterward.
Q: My new sink seems to be sagging slightly even after tightening the clips. What should I do?
A: This usually means the best adhesive for undermount sink (the silicone) needs more time to cure, or the clips are not applying enough upward pressure. First, let the silicone cure for the full 24 hours. If sagging continues, carefully loosen the clips slightly, apply temporary support blocks (2x4s propped up from the cabinet base against the sink bottom), and then re-tighten the clips, pushing the sink up firmly against the counter one last time before letting it cure fully again.