Correct Gap Between Undermount Sink and Countertop


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An undermount sink should sit flush against the underside of the counter. Gaps between a sink and counter are a sign of poor installation or failing components. The issue will need to be tackled with caulking, replacing support clips, or replacing the sink or counter.

Undermount sinks offer a sleek and seamless look, a little extra counter space, streamlined cleaning, and you can hide the caulking that is often visible on drop-in sinks. But, your undermount sink is only as good as its fit to the countertop.

The question is not how large the gap between an undermount sink and countertop should be. The question is should there be any gap there at all. Gaps are a sign of poor or failing installation and need to be addressed. However, there are other “gaps” to consider, namely the distance between the top of the counter and the top of the sink, visible sink lips, and countertop overhang.

There Should Be No Gap Between Sink and Counter

An undermount sink is installed sitting against the underside of the countertop—or, at least, it should be.

Undermount sinks can have three different types of reveals:

  • Positive: the counter connects in a way that shows some of the sink rim.
  • Negative: the counter overhangs slightly beyond the sink rim.
  • Zero: the counter is aligned precisely with the sink rim without exposing or overhanging it.
Undermount Sink & Countertop Reveal Styles: Positive Rveal, Zero Reveal, Negative Reveal

You should never have a gap between the counter and the sink with any of these reveal styles. The sink should be installed flush with the bottom of the countertop.

Problems With a Gap

Any gaps will prevent you from sealing the sink edge correctly. This will result in difficulties with dirt and grime building up in the spaces (that are not easy to clean) and making the whole area a little less hygienic.

Gorilla 8090001 2.8 Ounce Squeeze Tube Clear Silicone Sealant, 1-Pack

In the kitchen, you might find that crumbs and bits of food can get in there and become stale and rot. In the bathroom, you will likely have to clean out the sludge of old soap and other products from the deep recesses of your sink lip.

Without proper sealing, water is also able to gather in those spaces. Having water there can cause the growth of mold and mildew. It can also potentially damage your countertop (if it’s more porous) and can get into your cabinets.

If water can get into and sit inside your cabinets, you will likely experience problems with the finishes inside, problems such as peeling and warping. The wood of your cabinets can even rot and require complete replacing.

Having water leaking into a cabinet will also make it challenging to use as anything you store there would have to stand in water or get wet. Not to mention the damp smell you will have to deal with. So, a gap between your undermount bathroom sink and the countertop affects what you can and cannot store beneath the sink

Why Would There Be a Gap?

It is important to install the sink (or make the cut-out) before fitting the countertops. If your sink is installed after the counters, the fit will be less precise.  

A poor fitting can result in gaps between the counter and sink. This will also make it difficult to seal the sink to protect it from water damage and mold.

Kraus KD1US33B Dex 33-inch Undermount 16 Gauge Stainless Steel Single Bowl Kitchen Sink, Radiant Pearl Finish

If the sink is incorrectly sized, you might end up with a large gap because of the difference between the hole cut from the counter and the too-small sink.

Another and more urgent potential cause might be the supports. Due to the weight of the undermount sinks, they are installed using supports and adhesives. If the supports are not securely in place or the adhesive is not permitted to dry fully, your sink may be separating from your countertop and be on the verge of collapsing entirely.

How to Fix a Gap Between Undermount Sink and Counter

Caulking

There is always going to be a small gap. That is because sinks aren’t designed to make an airtight seal with your countertop. However, this small space is intended to be caulked over and sealed. If you are struggling because the sealant is incomplete or damaged, you will need to remove and redo it.

After you cut and peel off the old caulk, you need to buy appropriate caulking, such as the GE Supreme Silicone Kitchen and Bath Sealant Clear (amazon link), and re-seal the sink. You can use your finger or a grout tool to smooth out the seal around the sink’s edge.

Replace the Supports

Undermount sinks are held up to the counter using support clips. If these clips are old, worn, or damaged, you may find that a gap has developed. You will need to remove the sink, clean up the area, and reinstall the sink with new supports.

If the gap is severe, you may need to consider replacing the sink with one of suitable dimensions. You will need to remove the sink and clean off all the previous silicone adhesives before installing the new sink.

Both the videos below and this video offer helpful advice on how to remove and install an undermount sink:

Redo the Countertop and Cut-out

Or perhaps, if your sink was the more expensive items between it and your countertop, you may consider replacing that section of countertop. If you replace the counter, you can install a countertop with an accurate cut-out for your sink.

DIY sink cut out in butcher block countertop:

DIY sink cut-out and polish with granite:

Distance Between Counter Surface and Top of Sink

The undermount sink is designed to sit below the level of your counter.

If you are looking for a sink that sits flush with the top side of your counter, then you might be interested in an integrated sink. These are designed for a continuous surface without the bulge of drop-in sinks or the dip of undermount sinks.

The distance between your counter surface and the top of your sink is going to depend on the thickness of your countertop material. If you are looking for a less prominent line of countertop around the sink, then I recommend looking at your options for the material you are interested in.

Kraus KHU100-32 Standart PRO 16 Gauge Undermount Single Bowl Stainless Steel Kitchen Sink, 32 Inch

Granite and marble, which are popular choices with the undermount sink style, are available in thicker and thinner sheets because the thin sheets still have the necessary strength.

Should the Undermount Sink Lip Be Visible?

Your undermount sink lip can be visible if you opt for a positive reveal installation. This reveal fits the counter to the outer edge of the sink rim and leaves the lip exposed as a stylistic choice.

Pros

  • It requires less precision for the fitting.
  • It makes cutting the counter easier.
  • It offers a professional finish.

Cons

  • It makes cleaning more difficult as dirty and grime tend to gather on the exposed lip.
  • It detracts somewhat from the convenience of being able to sweep crumbs and mess directly into the sink as these things get caught on the lip.
  • Water can gather on the lip, which increases the potential for mold growth.

Should the Countertop Overhang the Sink?

Another reveal choice is the negative reveal. This is when the sink is fitted so that there is an overhang of the countertop over the rim of the sink. It creates a more integrated look for the sink space, having the counter almost disguise the sink.

The standard length of overhang on a negative reveal is 1/8”.

Pros

  • It creates a cohesive and continuous look.
  • It is easy to clean as dirt doesn’t gather on the lip of the sink.
  • It offers more leeway with the fitting as the edges don’t need to align perfectly.

Cons

  • The edges of your countertop are going to experience more wear and, as a result, are prone to damage such as chipping.
  • The overhang can easily hide dirt, mold, and mildew.

Sources

https://graniteselection.com/blog/how-to-install-undermount-sink-on-granite-countertop/

https://www.sinaarchitecturaldesign.com/2019/01/1656/

https://mensarjor.com/blogs/news/everything-you-ever-wanted-to-know-about-undermount-kitchen-sinks

https://www.apartmenttherapy.com/undermount-sink-kitchen-pros-cons-257717

https://www.hunker.com/13719385/what-is-an-undermount-sink

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