Undermount Sink Installation

These days, kitchens are designed to look modern, sleek and more efficient, and this has made the undermount sink more popular.

Apart from its simplified look, homeowners favor it because of its ease of cleaning: simply wipe debris and food straight into the sink where it goes directly into a waste disposer.

Since the sink is connected beneath the countertop, the sink capacity – both its weight and that of its contents – must be carefully considered.

For instance, consider a regular 22” x 33” cast iron or stone sink, when filled 5” with water it can weigh up to 125 lbs before any pots, dishes or silverware go in.

At this weight, maximum caution and skill is required to secure this kind of sink.

The majority of undermount sinks are composed of cast iron, stone, stainless steel, or china.

Therefore, the material of the countertop has to provide support for the sink’s hanging weight and waste disposer (if any), together with that of its contents – dishes or water.

Note that there is the possibility of vibrations caused by the disposer on the sink and attached area on the countertop.

For this sink type, a solid counter of stone-like material, marble, or granite works best, and also a system for kitchen support.

Undermount Sink Installation: Preparation

One thing that distinguishes the undermount sink from a typical drop-in sink is the precise cut of the hole to fit the sink measurement.

Despite the obvious, it is noteworthy that having the sink available before cutting the countertop for mounting is most essential. This is to make sure of the cut accuracy.

Before mounting the sink you’ll have to prep the countertop.

Start by smoothing the hole edges with sandpaper so as not to cause any damage to the sink. Then, use acetone and a clean cloth to clean off stains and dust from the opening and the countertop.

Ensure that the surface material (wood, stone, granite, or concrete) dries properly after cleaning so that the adhesive can work effectively.

Use wooden braces from beneath the countertop to the cabinet deck to hold the sink steady as you glue it and as it gets dry.

Undermount Sink Installation: Getting Started

Installation of the sink can be by gluing it to the countertop with the use of sealant or having the sink attached to studs with tight-fitted brackets drilled into the bottom of the countertop, or even both.

Pro Tip:

We recommend using easy-to-install kitchen undermount sink rails which bypass a lot of the following steps. These kits have their installation guides which are easy to follow.

Gluing is preferred however, and more frequently used in bathroom sinks installation – where there’s no need to drill beneath the countertop for the support studs.

This could reduce the strength of the surface material and damage it.

If you choose to use glue, apply a constant bead (1/2” or so) of sealant – like latex or silicon, or whichever the manufacturer recommends – around the undermount sink perimeter.

Use clips to hold the sink to the counter.

Clips are available in different kinds: some have a drilled stud epoxied into the counter with a nut which tightens the clip, while others have a strong split epoxy mounting it to the counter.

Here, before tightening clips or leveling caps and bolts, you need to adjust the sink’s position. You should do this before the sealant has set, so you can fit it properly in the countertop hole.

Undermount Sink Installation: Post Install

Typically, 24 hours should be given for the epoxy and sealant to set properly before the wood braces are taken out, or plumbing is connected, or the sink used.

This would ensure the sink does not move and break the impermeable seal.

Read our article on garbage disposal maintenance next!