How To Install an Undermount Bathroom Sink

Table of Contents

Fitting an under-mount bathroom sink on a countertop is our goal today. We will guide you to install them on your own that will save a lot of money and also allow you to increase your budget on the sink. During the installation you have to take a lot of precaution during fitting as the weight of an under-mount sink can be massive and yes, it won’t be easy as installing a bathroom faucet. Most of the top quality bathroom sink come with the brackets and all the required accessories so it won’t cause you any a headache.

So without further indulging anymore in the introduction, let’s start with the tools that you will need during the entire installation process.

Step by Step Guide to Install an Under Mount Bathroom Sink

Tools You Will Need

Calking gun.
Transparent Silicone or Epoxy resin adhesive.
Utility knife.
Nut driver.
Mounting hardware tape.
Electric drill.
Screw gun.
Bar Clamps.
80 grit sandpaper.

1. Making Space for Sink Top on The Counter

1.1 An under-mount sink is different than standard vessel sinks. It needs you to create a designated hole in the counter to install them. Moreover, the under-mount sink comes in different sizes and types, and you need to have them in your possession before beginning your cutting process.

You should adequately measure the breadth and length of the sink, and then compare it with the measurement given in the manual book of the pan. However, for safety purposes, you should flip the bathroom sink and mark the area of the drill. This will help you to cut the space for the sink in the countertop precisely.

You should cross-check your measurement with the marking on the countertop because a single mismatch can jeopardize the whole installation process. You should also make a hole or space for installing your new high-quality bathroom faucet along with the sink.

1.2 After taking the correct measurement, begin your cutting process, and it is advisable to accept help from family members or friends. You should use an electric drill with a 3/8inch bit and saw to cut the specific area for the sink. While cutting down the hole for the pan, you should use keyhole saw for accurately slashing the corners. You shouldn’t hurry during this time and try to cut it from the top because it will notch down the chance of error.

Although if you have massive granite or some other stone on your countertop, we would suggest you take help from professionals. They carry the technical skills and equipment to cut massive granites or marbles without causing damage to other parts.

2. Preparing The Countertop

2.1 Now, it is time to prepare the countertop for the mounting the under-mount washbasin but before buckle yourself to attach to you need perform some prior tasks. First, you need to use sandpaper and smoothen the edges of the hole so that it won’t damage the sink body.

Then use clean cloth and acetone or regular wet cloth to clean all the dust as well as stains on the countertop. After cleansing the top, you should also use acetone to wipe around the edges of the lower section of the countertop as debris or dust can hinder the adhesive prowess.

You should allow the granite, wood or any other material to get dry after cleaning otherwise the adhesive might not work correctly on a wet surface.

2.2 Now, flip the countertop and mark the areas where you will make holes for mounting the sink. Then with the help of an electric drill make a hole for attaching clamps or screws and clean the holed area with acetone as it will make the surface smooth.

2.3 Apply an adequate amount of silicone or latex with the help of caulking gun around the top edges of the under-mount basin. To stay safe, you can even apply silicone on the edges of the hole that you have made on the countertop. Then precisely place the under-mount washbasin on the shaft of the countertop and check whether it is the center position.

You can even take help from someone so that the washbasin can line up correctly with the hole on the countertop as they are quite heavy. Now, either you can apply a little amount of pressure or leave it as it is so that it can adhere appropriately to the silicone.

You can even glue the sink with the countertop without flipping it, but it would take the right amount for the seal to get thick. Moreover, you will need sturdy mounts to hold the sink securely, and it is quite hectic to continue the installation process from the underside of the tub.

There are many occasions, where a user tried to install a basin from the lower side of the counter and due to gravitational pull, the sink fell down on the ground as the sealant didn’t get time to get dried up.

2.4 After the sink gets attached to the lower section of the countertop, it is time to place the mounting clips that will secure the position of the pan. These mounting clamps are metal clips that can hold heavy washbasin easily without damaging the countertop.

Then mark the areas where you put the mounting clips and then make a hole in those areas with the drill. Then you have to use screws to the mounting clips that will attach both bodies together; however, it might cause some silicone to come out due to pressure. You can use a drill bit as it will properly tighten the screws properly which might not be possible standard screwdrivers.

So after mounting the clips, you should allow the adhesive to get dry for at least 8 hours, but it would be ideal if you will enable them to rest more than 20hours.

While drilling holes and tightening screws, you should be careful with the pressure otherwise you might damage the top layer of the countertop. After you sink down the screws in the hole, it will squeeze out some silicone so you can use acetone or normal wet cloth to clean them.

2.5 With the sink installed in the countertop, now it is time to fix your new faucet and for that place the tap on the counter for marking the area. Then with the help of drill and hand saw make a proper hole for inserting the lower section of the faucet. Be careful while you prepare the hole as a single inch mismatch will create a gap that won’t be suitable for the installation.

Even if you replace a bathroom faucet, we will recommend you correctly measure the diameter because once the countertop is flipped, you won’t be able to do much.

3. Putting The Sink In Place

3.1 When the silicone adhesive gets dries up after a long hour, slowly flip the countertop on the bathroom vanity with the sink attached to the bottom. Before flipping, take your caulking gun along with silicone and apply them on the edges of the base counter.

You should use a thick layer of silicon on the base counter so that it properly get attached to the top shelf. Ask one of your family members to hold one side of the countertop and another member to keep the sink properly. Then carefully place the pan over the bathroom vanity or base counter.

While you place the top counter over the base counter it will spill some silicon on the edges of the top, so you need to clean them immediately otherwise it would get thick. Some specific countertop models might require screws and clips for attachment to the base counter, so it would be ideal to follow the manufacturer’s instruction before applying glue.

3.2 Once you have placed the countertop over the base counter, you are ready to install your faucet in the hole. First, you have to attach plastic or rubber gasket attach to the table and then place the tap over it. Next, use the washer along with nut to bolt down the faucet in place, and you should use your wrench to secure them properly.

Then move to the lower side of the base counter and attach the tail end of the faucet with another washer and bolts. You can even use putty or silicone adhesive to keep the lower section intact in its position. This same step should be applied to other handles only if you are installing a widespread faucet on the countertop.

3.3 After attaching the valve in place, you will have to opt for the installation of a washbasin drain or pop up drain. First, you will have to take the drain cover and apply silicone or putty on the lower section of the pipe. Then quickly place the drain cover over the drain opening and apply pressure so that it gets adequately placed in the hole.

Wipe out the excess silicone or putty from the basin otherwise, it will look tacky. After putting it, go to the lower section and use screws to tighten the drain cover. Once all the equipment is in their respective, you should allow the base counter adhesive, bathroom faucet silicone and drain cover adhesive to get dried.

4. Assembling The Lines

4.1 In this phase, you will have to connect all the water lines and drain lines so you can complete the whole setup. First, attach the drain line with the drain opening, and it is advisable to use connectors to seal the connection areas. You can even use plumber’s tape for sealing the connection as it will slash down any leakage.

4.2 With the faucet end pipes in position, hook all the water lines with the faucet but remember you shouldn’t get confused between cold water and hot water line. The water line alignment should be correct otherwise you might not get a proper force. Similarly, it would be ideal to use the P trap as it will be safe and will secure connectivity.

5. Test What Have You Done So Far!

5.1 So, now when everything is in the order you will first turn on the central water knob and then open the faucet to check the water flow. It will also allow you to check if there is any leak in the connectivity. However, if you face any leakage in any area, then you can either tighten the screw in that section or else you tape or putty to seal them.

Some Considerations:

You can also attach your under-mount sink to the counter-top without making drills, and you just need to use some silicone sealant along with epoxy. However, it entirely depends upon the weight of the under-mount sink, and it is only applicable for lightweight to middleweight sinks.
Although it is altogether a simple DIY process it is advisable to keep one family members or friends to accompany. As you will be dealing a lot of heavy equipment and it is not easy for everyone to handle them by self. A silly miscalculation cause damage to the bathroom equipment and your health.

Related Articles:

Pat Abbaticchio

Pat is the former Luxury Sales Specialist of Groupe Deschenes. He has experience of 15+ years in the home improvement industry. He is now the Senior Sales Officer at The Rubinet Faucet Company.