Can I install an undermount sink myself? Yes, you can install undermount sink units as a capable DIY homeowner. This guide will show you step-by-step how to do it right. An undermount sink sits beneath your countertop. This looks clean and makes wiping spills easy. It is a popular choice for granite, quartz, and solid surface counters.
Why Choose an Undermount Sink?
Many people like undermount sinks. They offer a sleek, modern look. There is no rim sitting on top of the counter. This means you can sweep crumbs right into the basin. This makes cleanup much simpler than with a drop-in sink.
Preparing for Your New Sink
Before you start the actual undermount sink installation guide, good planning is key. You need the right tools and the right sink.
Tools and Materials Checklist
Gather everything before you begin. Having all parts ready saves time later.
- New undermount sink basin
- Undermount sink template (usually comes with the sink)
- Measuring tape and pencil
- Jigsaw or specialized countertop cutting tool (if cutting new stone)
- Drill and appropriate bits
- Clamps or specialized undermount sink mounting hardware
- Plumber’s putty or silicone sealant (undermount sink adhesive)
- Adjustable wrench
- Safety glasses and dust mask
- Support system (if your countertop is not stone, like laminate)
Removing the Old Sink (If Applicable)
If you are replacing an existing sink, you must remove it first.
- Turn Off Water: Locate the shut-off valves under the sink. Turn both the hot and cold water lines completely off.
- Disconnect Plumbing: Use a wrench to disconnect the supply lines from the faucet. Then, disconnect the drain lines and garbage disposal (if present). Keep old towels handy for drips.
- Remove Clips/Sealant: Look underneath the sink. You will see clips or screws holding it up. Remove these.
- Loosen the Seal: The sink rim is glued to the bottom of the counter. Use a utility knife to carefully cut through the old caulk or sealant around the edge. Be gentle to avoid scratching the counter.
- Lift Out: Have a helper assist you. Push the sink up from below and lift it out of the counter opening.
Step 1: Marking and Cutting the Countertop Hole
This step is critical, especially if you have a solid surface counter like granite or quartz. Cutting countertop for undermount sink requires precision.
Using the Template
Your new sink should come with an undermount sink template. This cardboard or plastic guide shows the exact hole size needed.
- Positioning: Place the template exactly where you want the sink to sit. Make sure it allows equal space from the backsplash and sides.
- Tracing: Trace the inner cutout line onto the countertop surface using a fine-tipped marker. This line shows where the sink opening will be.
- Faucet Placement: If your faucet mounts on the counter (not the sink), mark those holes now too, using the template or faucet specifications.
Making the Cut
If you have a laminate counter, this is easier. If you have stone, you need specialized tools.
- Stone Countertops (Granite/Quartz): You must use a water-cooled diamond blade saw or jigsaw designed for stone. Always wear safety gear. Go slowly. Water cooling prevents the stone from cracking due to heat.
- Laminate Countertops: A standard jigsaw works well here. Drill pilot holes in the corners of your traced line first. This gives you a place to insert the jigsaw blade. Cut along the line carefully.
The Support Reveal
For an undermount sink, the opening must be slightly smaller than the rim of the sink. The rim needs something to rest on.
- Check your sink’s specific mounting instructions. Often, you trace the drain opening size, not the whole sink flange size.
Step 2: Preparing the Sink and Countertop Surfaces
Clean surfaces ensure a strong, lasting bond. You are sealing undermount sink to countertop, so everything must be dry and dust-free.
Sink Surface Prep
- Clean the Rim: Wipe down the top edge (the rim) of the sink basin thoroughly with rubbing alcohol. This removes any manufacturing oils. Let it dry fully.
- Dry Fit: Place the sink in the opening briefly without sealant. Check how it sits. Does the rim rest evenly on the counter surface?
Countertop Surface Prep
- Clean Underside: If you are dealing with an existing opening, clean the area under the counter where the rim will rest. Remove any old adhesive, dust, or grease.
- Test Fit Support: If you have a material that needs extra support (like wood cabinetry under laminate), ensure your support structure is ready now.
Step 3: Installing Faucet Hardware (If Applicable)
It is much easier to install undermount sink hardware like the faucet before the sink is mounted. Once it’s glued up, you can’t reach underneath easily.
- Faucet Assembly: Follow the faucet manufacturer’s directions to assemble the faucet body and handles.
- Mounting: Feed the water lines and mounting shank through the pre-drilled holes in the countertop (or through the sink holes if it’s a sink-mount faucet).
- Securing: From underneath, use the provided washers and mounting nuts to tighten the faucet firmly in place. Do not overtighten, especially on stone, which could crack.
Step 4: Applying Sealant and Mounting the Sink
This is the core step where you affix the sink permanently. We use undermount sink adhesive for this.
Applying the Sealant
- Choose Your Sealant: Most professionals use 100% silicone caulk designed for kitchens and baths. This remains flexible and waterproof.
- Application: Run a thick, continuous bead of silicone sealant along the entire underside rim of the sink. This bead should be generous enough to ooze out slightly when pressed, ensuring a full seal.
Positioning the Sink
- Get Help: This is a two-person job. Carefully lift the sink with the sealant applied.
- Lower Into Place: Slowly guide the sink rim up into the countertop opening. Align it perfectly with the traced lines.
- Press Firmly: Apply downward pressure evenly across the entire rim. You should see some excess silicone squeeze out around the edge underneath the counter.
Step 5: Securing an Undermount Sink with Mounting Hardware
Silicone alone is not enough for a heavy sink. You need mechanical fasteners. This is where undermount sink mounting hardware comes into play.
Types of Mounting Systems
Different sinks use different methods for securing an undermount sink:
| Hardware Type | Description | Best Used For |
|---|---|---|
| Clips/Brackets | Metal clips that screw into the cabinet base or underside of the counter overhang. | Granite, Quartz, heavier sinks. |
| Strap Systems | Long metal straps that loop around the sink basin and bolt to support braces. | Deeper sinks or weaker materials. |
| Adhesive Blocks | Epoxy blocks adhered directly to the counter, which the sink mounts onto. | Specific manufacturer systems. |
Using a Clip System for Undermount Sink
The clip system for undermount sink is very common.
- Install Support: If using wooden supports, screw them into the cabinet frame now.
- Position Clips: Place the metal clips or brackets around the sink flange. They should contact the underside of the countertop material.
- Tighten: Using a socket wrench or screwdriver, gently tighten the screws on the clips. Tighten them incrementally, moving around the sink in a crisscross pattern (like tightening lug nuts on a tire). This ensures even pressure.
- Goal: Tighten until the clips firmly hold the sink rim against the countertop. The silicone should be squeezed slightly, but the stone or counter material should not crack under pressure.
Alternative: Using Epoxy Support Blocks
Some high-end installations rely on specialized epoxy mounting blocks bonded directly to the stone. These require specific curing times before connecting the sink. Follow the block manufacturer’s instructions strictly.
Step 6: Installing the Drain Assembly and Flange
The drain assembly connects the sink basin to your plumbing. This involves the undermount sink flange installation.
Installing the Sink Flange
For most undermount sinks, you use a basket strainer assembly that includes a metal flange that sits flush against the bottom of the sink basin.
- Prepare the Flange: Wrap the threads of the sink flange with plumber’s putty or apply a bead of silicone sealant where it meets the sink bottom.
- Insert: Push the flange assembly up through the drain hole from the top side of the sink.
- Secure From Below: From underneath the sink, slide the friction ring (if provided) and then the large mounting nut onto the flange threads.
- Tighten: Hand-tighten the mounting nut first. Then, use channel locks to tighten it firmly until the putty/sealant squeezes out slightly around the flange top inside the sink bowl. Wipe away excess putty from the bowl immediately.
Connecting the P-Trap
- Tailpiece Connection: Attach the drain tailpiece to the bottom of the newly installed flange assembly.
- P-Trap Alignment: Connect the P-trap to the tailpiece and align it with the waste pipe coming from the wall.
- Assembly: Use slip nuts to join the pieces. Hand-tighten these connections first, then give them a slight turn with pliers to ensure a seal.
Step 7: Final Curing and Cleanup
Patience pays off here. You must let the adhesive set before testing for leaks.
- Curing Time: Allow the silicone sealant to cure completely. This usually takes 12 to 24 hours, depending on humidity and the specific product used. Check the tube instructions. Do not run water or put heavy items in the sink during this time.
- Remove Excess Sealant: Once cured, look at the seam where the sink meets the counter from above. If any silicone squeezed out onto the counter surface, use a razor blade held at a very shallow angle to gently scrape away the excess.
- Final Inspection: Once the silicone is cured, reconnect the water supply lines and run water down the drain. Check all drain connections (flange, tailpiece, P-trap) for leaks. If a leak occurs, dry the area and tighten that specific joint slightly more.
Comprehending Countertop Material Challenges
The material of your countertop greatly affects the undermount sink installation guide.
Granite and Quartz (Engineered Stone)
These are durable materials perfect for undermount sinks. They are very heavy, so robust undermount sink mounting hardware is essential. These counters are strong enough to support the weight and the clips. Cutting requires specialized diamond tools.
Solid Surface (Corian, etc.)
These materials are softer and usually installed using a combination of adhesive and specialized clips built into the material’s support structure. Cutting is easier than stone.
Laminate Countertops
Laminate is the trickiest. You cannot truly undermount laminate because the particleboard core will absorb water and swell if exposed, ruining the counter and the seal.
- The Solution: If you have laminate, you must install a custom sink flange installation lip that acts like a barrier or use a specialized sink designed to be “flush-mount” rather than true undermount. Most experts advise against true undermount sinks with standard laminate.
Troubleshooting Common Installation Issues
Even with careful work, problems can arise. Here are solutions for typical difficulties faced during the install undermount sink process.
Issue 1: Sink Sits Too Low or Too High
- Cause: Incorrect tracing or cutting of the hole, or using the wrong support system.
- Fix: If too low, you need thicker shims or different mounting brackets to raise the sink until the rim contacts the counter properly. If too high, the hole needs careful enlarging (difficult with stone).
Issue 2: Leaking Drain Flange
- Cause: Not enough plumber’s putty or silicone, or the securing nut was not tight enough.
- Fix: Drain the water. Dry the area completely. Reapply putty/sealant around the flange threads and tighten the mounting nut firmly.
Issue 3: Clips Won’t Tighten Properly
- Cause: Screws are hitting wood studs inside the cabinet, or the clips are not reaching the underside of the counter overhang.
- Fix: For metal clips that miss the stone, you may need to use small pieces of wood or epoxy anchors secured to the stone edge to give the screws something solid to bite into. Ensure your undermount sink mounting hardware is designed for your counter thickness.
Issue 4: Silicone Sealant Smears on Countertop
- Cause: Applying too much sealant or wiping it poorly during the initial setting.
- Fix: Wait for the sealant to fully cure (12-24 hours). Then, use a fresh, sharp razor blade held almost flat against the counter surface to gently shave off the cured excess.
Frequently Asked Questions (FAQ)
Q: Do I need a special garbage disposal for an undermount sink?
A: Generally, no. Most standard garbage disposals mount the same way. However, you must ensure the disposal flange fits securely into the drain opening and that you use the correct undermount sink flange installation technique for your sink material.
Q: Can I use construction adhesive instead of silicone sealant?
A: While some heavy-duty construction adhesives (like Liquid Nails) are strong, standard 100% silicone is preferred. Silicone stays flexible, which is important as the sink and counter expand and contract slightly with temperature changes. Flexible sealant prevents cracking the seal.
Q: How much space should there be between the sink rim and the cabinet wall?
A: You need enough room to access the undermount sink mounting hardware. For clips and brackets, you usually need at least 1.5 to 2 inches of clearance between the sink rim and any vertical cabinet structure so you can get a tool in to tighten the screws.
Q: What if my countertop material is only 1.25 inches thick?
A: Thicker stone (1.5 to 2 inches) is ideal. If your stone is thinner, you must use specialized hardware. Look for clips that grip the thinner edge securely or opt for heavy-duty epoxy blocks instead of traditional screws, as screws might punch through the thin stone edge.
Q: Is it harder to clean around an undermount sink?
A: No, it is easier! Because there is no rim lip, you can simply sweep all food debris and liquid directly from the countertop into the basin without stopping at an edge. This is one of the main benefits of this type of sink.