How to Replace Undermount Kitchen Sink: DIY Guide

Can you replace an undermount kitchen sink yourself? Yes, you absolutely can! While it might seem like a daunting task, with the right tools, patience, and this step-by-step guide, you can successfully tackle an undermount sink installation as a DIY project. This kitchen sink replacement guide will walk you through the entire process, from undermount sink removal to making sure your new sink is perfectly in place. Replacing your kitchen sink is a great way to update your kitchen’s look and functionality without a massive renovation.

Replacing an undermount sink requires a bit more finesse than a top-mount sink because it’s installed from below the countertop. This means you’ll be working in tight spaces, often with limited visibility. However, the finished product – a sleek sink that appears to float on your countertop – is well worth the effort. We’ll cover everything you need to know, including how to detach undermount sink fixtures, properly secure undermount sink hardware, and the essential kitchen sink installation steps for a watertight and lasting result.

How To Replace An Undermount Kitchen Sink
Image Source: i.ytimg.com

Preparing for Your Undermount Sink Project

Before you dive in, proper preparation is key to a smooth and successful replace kitchen sink project. This involves gathering all the necessary tools and materials, and also making sure you have a clear workspace.

Tools You’ll Need

Having the right tools makes the job much easier and safer. Here’s a comprehensive list:

Safety Gear: Safety glasses, work gloves, a dust mask.
Wrench Set: Adjustable wrenches and pipe wrenches for plumbing connections.
Screwdrivers: Various sizes, both Phillips and flathead.
Pliers: Channel lock pliers are particularly useful for plumbing.
Utility Knife or Caulk Scraper: For breaking the seal around the old sink.
Pry Bar: A small to medium-sized pry bar can help loosen the old sink.
Putty Knife: For scraping away old sealant.
Bucket and Towels: To catch any residual water and clean up spills.
Stud Finder: To locate countertop supports if needed.
Drill/Driver: With appropriate bits for any screws.
Measuring Tape: To ensure accurate placement of the new sink.
Silicone Sealant: Specifically designed for kitchen and bath use.
Clamps: To hold the new sink in place while the sealant cures.
Plumber’s Putty or Wax Ring: For the drain assembly.
Caulking Gun: For applying sealant neatly.
Drop Cloths or Tarps: To protect your cabinets and flooring.
New Sink Clips/Mounting Hardware: Usually comes with the new sink, but good to confirm.
New Drain Assembly and Strainer: It’s often best to replace these with the sink.
Optional: Reciprocating Saw (Sawzall) with a metal cutting blade: If the old sink is particularly stubborn and you have a salvageable countertop. Use with extreme caution!

Materials to Gather

New Undermount Sink: Ensure it’s the correct size and style for your needs.
Faucet and Sprayer: If you’re replacing these as well.
Drain Pipes and P-Trap: If your old ones are worn or incompatible with the new sink.
Silicone Sealant: High-quality, kitchen-grade silicone.

Preparing Your Workspace

Clear Everything Out: Remove all items from beneath the sink and from the countertop around the sink area.
Protect Surfaces: Lay down drop cloths or tarps to protect your cabinet interior and flooring from water, debris, and sealant.
Turn Off Water Supply: Locate the hot and cold water shut-off valves under the sink. Turn them clockwise until they are completely closed. Test the faucet to ensure the water is off by turning it on. If you don’t have individual shut-off valves, you’ll need to turn off the main water supply to your house.
Disconnect Power: If you have a garbage disposal, unplug it from its electrical outlet or turn off the circuit breaker that powers it.

Step-by-Step: Undermount Sink Removal

This is often the trickiest part. The old sink is held in place by sealant and mounting clips.

1. Disconnect Plumbing

This is a crucial step in the undermount sink removal process.

Drainage: Place a bucket under the P-trap (the U-shaped pipe) to catch any water. Use your channel lock pliers or a pipe wrench to loosen the slip nuts connecting the drain pipes to the sink strainer and the wall pipe. Unscrew them carefully.
Water Supply Lines: Disconnect the hot and cold water supply lines from the faucet. Have a towel ready to catch any residual water. Use an adjustable wrench.
Garbage Disposal (if applicable): If you have a garbage disposal, it’s usually mounted to the sink flange. You’ll need to disconnect the disposal from the sink. There’s often a mounting ring that you can twist to release it. If it’s wired, ensure the power is off! You might need to support its weight as it’s heavy.

2. Loosen Mounting Clips

Undermount sinks are secured from underneath with clips that screw into the underside of the countertop or are attached to brackets.

Locate the Clips: Get into the cabinet space beneath the sink and look for metal clips around the perimeter of the sink bowl. They will be attached to the sink rim and screwed or bolted into the countertop.
Unscrew the Clips: Use a screwdriver or drill to remove the screws holding these clips in place. Some older installations might use adhesive or epoxy in addition to clips, which can make removal harder.

3. Break the Seal

The sink is also sealed to the countertop with silicone caulk.

Cut the Sealant: Insert a sharp utility knife or a specialized caulk removal tool between the sink rim and the countertop. Carefully cut through the silicone all the way around the sink. Try to keep the blade as parallel to the countertop as possible to avoid scratching it.
Scrape Away Old Caulk: Use a putty knife to scrape away any remaining caulk from both the sink and the countertop edge.

4. Gently Pry the Sink Loose

Once all plumbing and clips are disconnected and the seal is broken, the sink should be ready to come free.

Push from Below: If possible, gently push the sink upwards from the cabinet.
Pry Carefully: If it doesn’t budge, use your pry bar very carefully between the sink rim and the countertop. Work your way around, applying gentle upward pressure. Be cautious not to damage the countertop material, especially if it’s laminate, wood, or fragile stone.
Support the Sink: As the sink starts to loosen, be prepared for its weight. Have someone help you support it as you pull it down and out from under the countertop.

5. Clean the Countertop Opening

Remove Debris: Once the old sink is out, clean the countertop opening thoroughly. Scrape off any remaining sealant or adhesive with your putty knife and a mild cleaner. Ensure the surface is smooth and clean for the new sink’s installation.

Installing the New Undermount Sink

Now that the old sink is out, it’s time for the install new undermount sink phase. This is where we focus on the undermount sink mounting and ensuring a secure fit.

1. Prepare the New Sink

Inspect the Sink: Check the new sink for any damage.
Install the Drain Assembly: This is best done before you try to mount the sink.
- Apply plumber’s putty or a wax ring around the underside of the sink’s drain flange.
- Insert the flange into the sink drain opening.
- From underneath, slide the rubber gasket and then the friction ring over the flange.
- Thread on the locknut and tighten it firmly with pliers. Wipe away any excess plumber’s putty that squeezes out.
Attach Faucet and Sprayer (Optional but Recommended): It’s much easier to install the faucet and sprayer while the sink is accessible from below, before it’s permanently mounted. Follow the manufacturer’s instructions for your specific faucet.

2. Position the New Sink

This is a critical step for successful undermount sink installation.

Test Fit: Carefully lift the new sink into the countertop opening from below. Make sure it fits snugly and sits flush against the underside of the countertop.
Align Properly: Ensure the sink is centered and aligned correctly in the opening. Check that the drain hole is facing the correct direction for your plumbing.

3. Secure the Sink

This involves using clips or adhesive to secure undermount sink hardware.

Install Mounting Clips: Most undermount sinks come with specialized mounting clips. These typically screw into brackets that are either pre-attached to the sink or need to be affixed to them.
- Slide the clips into their designated slots on the sink’s outer rim.
- Tighten the screws on the clips that will press against the underside of the countertop.
- Important: Don’t overtighten at this stage. You want the sink to be held firmly but allow a little adjustment.

4. Apply Sealant

A good seal is vital to prevent leaks and keep your countertop protected.

Clean Countertop Edge: Ensure the underside edge of the countertop is perfectly clean and dry.
Apply Silicone: Run a continuous bead of high-quality silicone sealant around the entire perimeter of the sink rim that will contact the countertop. Use a caulk gun for an even application.

5. Final Sink Placement and Clamping

Press the Sink into Place: Carefully lift the sink and press it firmly against the countertop, ensuring the sealant makes good contact.
Tighten Clips: Now, go back and tighten the mounting clips securely. This will press the sink firmly into the sealant and against the countertop. You should see a small amount of sealant squeeze out around the edges – this is good!
Use Clamps: To ensure even pressure while the sealant cures, use clamps to hold the sink firmly in place against the countertop. Position the clamps between the sink rim and the cabinet base, or use specialized countertop clamps if you have them.

6. Reconnect Plumbing

Now it’s time to reconnect everything you disconnected earlier.

Water Supply Lines: Reconnect the hot and cold water supply lines to the faucet. Hand-tighten first, then give them a quarter to half turn with a wrench.
Drainage: Reattach the drain pipes and P-trap. Ensure all slip nuts are tightened securely but avoid overtightening, which can crack plastic pipes.
Garbage Disposal (if applicable): Rehang the garbage disposal, ensuring the mounting ring is properly secured. Connect the disposal’s drain outlet to the new sink drain assembly.

7. Test for Leaks

This is the moment of truth!

Turn Water On Slowly: Slowly turn the main water supply back on, or open the shut-off valves under the sink.
Check Connections: Carefully inspect all plumbing connections for any drips or leaks.
Run Water: Turn on the faucet and let water run for a few minutes. Fill the sink partially and then let it drain. Check all connections again, including the drain assembly and faucet base.
Tighten as Needed: If you find any leaks, gently tighten the connections.

8. Finishing Touches

Wipe Away Excess Sealant: Use a damp cloth or paper towel to wipe away any excess sealant that squeezed out around the sink rim before it cures. You can use a specialized caulk smoothing tool for a clean finish.
Clean Up: Remove all tools, drop cloths, and materials. Clean your work area thoroughly.
Allow Sealant to Cure: Check the sealant manufacturer’s instructions for curing time. Avoid heavy use of the sink or placing anything on the countertop that might shift the sink until it’s fully cured.

Table: Common Issues and Solutions During Installation

Problem	Cause	Solution
Sink won’t come loose during removal	Stubborn sealant, corrosion, or old adhesive.	Reapply heat with a hairdryer to soften sealant, use more force with a pry bar, or in extreme cases, a reciprocating saw with a metal blade (use with extreme caution and protect the countertop).
Leaks from drain assembly	Improperly seated flange, loose locknut, or bad putty seal.	Disassemble and reapply plumber’s putty to the flange. Ensure the rubber gasket is oriented correctly. Tighten the locknut firmly.
Leaks from faucet connections	Loose supply lines or improperly tightened fittings.	Tighten the supply line fittings slightly. Ensure rubber washers or seals are present and correctly seated.
Sink not sitting flush against counter	Uneven sealant application, debris on the surface, or warped sink.	Remove the sink, clean both surfaces thoroughly, reapply sealant evenly, and re-seat the sink. Ensure mounting clips are correctly positioned and tight.
Mounting clips won’t tighten properly	Stripped screw holes or incorrect clip type for the countertop.	For stripped holes, you might need to use a slightly larger screw or a wood filler/epoxy to rebuild the hole. Ensure you have the correct mounting clips for your countertop material.
Water backs up in sink	Clogged drain or improperly installed P-trap.	Check for clogs in the drain or P-trap. Ensure the P-trap is installed correctly with the U-bend facing downwards.
Countertop damage during removal	Too much force applied, sharp tools used carelessly.	For minor scratches, consider a countertop repair kit. For larger chips, professional repair might be needed. Prevention is key: use caution and the right tools.
New sink doesn’t fit opening	Incorrect measurements, or previous sink was slightly larger.	This is a major issue. If the opening is too small, you may need to slightly enlarge it with a router or jigsaw (carefully!). If it’s too large, you might need to use thicker sealant or a different mounting method, or consider a new countertop.

Frequently Asked Questions (FAQ)

How long does it take to replace an undermount kitchen sink?

The time it takes can vary significantly based on your experience level and the specifics of your old sink’s installation. For a DIYer, you can expect it to take anywhere from 4 to 8 hours. If you are also replacing the faucet and dealing with challenging plumbing, it could extend longer.

Do I need to replace my faucet when replacing my sink?

It’s not strictly necessary, but it’s often a good time to do so, especially if your faucet is old or doesn’t match the new sink. Installing a new faucet is much easier when the sink is out of the countertop.

What is the best type of sealant for an undermount sink?

High-quality kitchen sink installation steps always include using a premium kitchen and bath silicone sealant. Look for products specifically designed for sealing sinks to countertops. They offer excellent adhesion, water resistance, and flexibility.

Can I replace an undermount sink without removing the countertop?

Yes, the entire process of replace kitchen sink for undermount sinks is designed to be done without removing the countertop. This is a key advantage of undermount sinks.

How do I detach an undermount sink if it’s glued?

Some older installations might have used strong adhesives. If sealant alone isn’t working, you might need to use a solvent specifically designed for adhesives or carefully score the adhesive with a sharp utility knife. In very stubborn cases, a reciprocating saw with a fine metal blade, used with extreme care, might be necessary to cut through the bonding agent, but this carries a high risk of damaging the countertop.

What’s the difference between undermount sink removal and undermount sink installation?

Undermount sink removal involves disconnecting plumbing, breaking the sealant and clips holding the old sink in place, and carefully pulling it out. Undermount sink installation is the reverse: preparing the new sink, positioning it, securing it with clips and sealant, reconnecting plumbing, and testing for leaks.

How do I secure an undermount sink properly?

Secure undermount sink hardware typically involves specialized clips that screw into the underside of the countertop and press against the sink’s rim. Applying a generous bead of silicone sealant around the sink rim before pressing it into place is also crucial for a secure and watertight bond. Clamping the sink to the countertop while the sealant cures ensures a strong, even bond.

What are the main kitchen sink installation steps for an undermount sink?

The main kitchen sink installation steps for an undermount sink include: disconnecting the old sink’s plumbing, removing the old sink and all sealant/clips, preparing the new sink (installing drain, faucet), applying sealant to the new sink’s rim, positioning and securing the new sink with clips, reconnecting all plumbing, and testing thoroughly for leaks.

This comprehensive guide should equip you with the knowledge and confidence to tackle your undermount sink installation project. Remember to work patiently, prioritize safety, and don’t hesitate to consult additional resources or professional help if you encounter unexpected challenges. Enjoy your refreshed kitchen!