An undermount kitchen sink can add a sleek, modern look to your kitchen, but you need to make sure it’s properly secured. A loose or improperly installed sink can lead to water damage and costly repairs.
In the video above, This Old House plumbing and heating expert Richard Trethewey demonstrates how to secure an undermount kitchen sink and provides tips for dealing with common issues. In this particular project, Richard reattached an undermount sink to a granite countertop.
Common Causes of Loose Undermount Sinks
Undermount sinks attach to the underside of the countertop, creating a seamless look. They’re typically held in place with a combination of strong adhesive and mounting clips. However, over time, these attachments can deteriorate and fail, causing the sink to separate from the countertop.
Several factors can make an undermount sink become loose:
- Improper initial installation
- Deterioration of adhesive over time
- Corrosion of mounting hardware
- Excessive weight or stress on the sink
Typically, it is pretty obvious when your undermount sink is coming loose. You’ll start to see gaps between the sink and the countertop and water seepage around the sink edges. You’ll also notice unusual movement or shifting of the sink when in use.
Tools and Materials Needed
Before you start securing your sink, gather the following tools.
Screwdriver- Wrench
- Caulk gun
- Putty knife
You’ll also need these materials:
- Silicone caulk
- Undermount sink clips
- Wood braces
Steps To Secure an Undermount Kitchen Sink
Follow these steps to properly secure your undermount kitchen sink.
Step 1: Turn Off the Water Supply
Locate the valves under the sink and turn them off. If there is no valve under the sink, turn off the main water supply line.
Step 2: Disconnect Plumbing Connections
Using an adjustable wrench, disconnect all plumbing connections from the sink, including the faucet supply lines and drainpipe. After loosening the pipes, carefully pull them away.
Step 3: Remove Remaining Sink Clips
From underneath the sink, use a screwdriver to remove the metal clips that are holding the sink against the countertop. If these clips are corroded or damaged, you might need a pair of pliers for extra leverage.
Step 4: Lower and Set Aside the Sink
Once all clips and connections are removed, carefully lower the sink. Be cautious, as the sink may still be attached with adhesive. If needed, use a putty knife to gently pry it away.
Step 5: Clean Off Old Caulking
Using a putty knife, scrape off the old silicone caulking from both the sink and the underside of the countertop. This helps the new caulk adhere better.
Step 6: Insert New Sink Clips
Align new undermount sink clips with the existing holes on the underside of the countertop. If holes are not available or damaged, carefully drill new ones, taking care not to crack the countertop.
Step 7: Loosely Screw Machine Screws
Put the machine screws into the brass insets but do not tighten them all the way. This allows some adjustment when positioning the sink back into place.
Step 8: Apply Silicone Caulk
Using a caulk gun, apply a thick bead of silicone caulk around the rim of the sink. Make sure the bead is even, as this creates a watertight seal between the sink and the countertop.
Select a high-quality, waterproof silicone caulk specifically designed for kitchen use. This type of caulk provides excellent adhesion and flexibility. To ensure a proper seal:
- Clean and dry the surface thoroughly before applying caulk.
- Cut the caulk tube nozzle at a 45-degree angle.
- Apply a consistent bead of caulk around the sink rim.
Step 9: Lift the Sink Back into Place
Carefully lift the sink and fit it back into the cutout from underneath, aligning it with the countertop.
Step 10: Tighten Machine Screws
Once the sink is in place, tighten the screws from below. This will pull the sink tight against the countertop, creating a secure attachment.
Step 11: Place Wood Braces Below the Sink
Use wood braces or any reliable supports under the sink to hold it up firmly while the caulk cures. This ensures that the sink doesn’t shift or fall out of alignment.
Step 12: Smooth Out Excess Caulk
Use a damp cloth or your finger to remove any excess caulk that squeezes out from the rim.
Step 13: Reconnect the Plumbing and Turn the Water Back On
Finally, reconnect all the plumbing connections you originally disconnected. Restore the water supply and check for any leaks or issues.
Step 14: Wait 24 Hours Before Use
Wait 24 hours before removing the wood braces or using the sink to allow the caulk to cure.
DIY vs. Professional Installation of an Undermount Kitchen Sink
You can secure an undermount sink on your own, but be honest about your skill level and the job’s complexity first. We recommend hiring a pro if you aren’t familiar or comfortable working with plumbing, or if the countertop material is delicate, expensive, or significantly damaged.
Professional installation often includes warranty protection for both labor and materials, providing valuable peace of mind. Plus, professionals are equipped to address any unexpected issues that may arise during the installation, securing all components and minimizing the risk of future problems.
Maintaining Your Undermount Sink
Regular maintenance can help prevent your undermount sink from becoming loose again. To prevent undue stress on the sink, follow these recommendations:
- Avoid sitting or standing in the sink
- Don’t overload the sink with heavy pots or appliances
- Use a sink grid to distribute weight evenly
Keep your sink clean and dry when not in use. Wipe down the sink and countertop regularly, especially around the edges, where water can seep and damage the adhesive or mounting hardware. Periodically check for signs of loosening or water damage:
- Look for gaps between the sink and countertop
- Check for moisture or water stains under the sink
- Test for any movement or shifting of the sink
If you notice minor issues during your inspections, address them before they become significant problems. For instance, reapply caulk if you detect any gaps or cracks, and retighten any loose screws or clips.
