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View Full Version : How sanitary are undermount sinks?



Stephen Tashiro
06-21-2018, 12:01 PM
The undermount sink installations that I've seen leave a lip on the underside of the countertop. It seems to me that this hidden surface would get filthy after the sink has been used for awhile. Is this hidden area a standard feature of undermount sinks? - or are they supposed to be installed so the sides of the sink are exactly even with the countertop above them?

Bruce Volden
06-21-2018, 12:49 PM
I installed an over size farm sink 2+ yrs. ago. It too sits about 3/4" under the granite counter except for the front. Once the sink was installed, the area between sink and counter was filled
with RTV? /silicone caulk--can't remember--no problems to date. There is no "lip" per se because of the caulk. HTH

Bruce

Perry Hilbert Jr
06-21-2018, 1:56 PM
We had an undermount stainless sink mounted under a granite counter. The sink is scrubbed out at least once a week, including running a scrub brush around the lip. Had the sink for three years now, but with only two adults in the house, the sink tends to stay fairly clean anyway. When the adult children (slobs) are here, the sink gets a thorough cleaning more often. I really do not understand why someone would take a greasy frying pan, put it in the sink and then stack dishes and drinking glasses in it so they can get as greasy too.

Dan Friedrichs
06-21-2018, 2:52 PM
The ones I've had/seen never have a visible overhang of the counter into the sink bowl - they're flush. There is a small gap due to the necessary radius between the sink side and flange, but this is caulked.

Personally, I like the undermount sinks that are built with a solid-surface material making the sink and counter a contiguous unit.

Bob Grier
06-21-2018, 3:42 PM
A word of caution on some sinks. The stainless sink I purchased included a template for cutting the countertop. I gave this to the granite people along with a caution to cut the opening to match the template or the sink would not work properly. The sink included accessories like drain rack and cutting board that sit on a 45 ledge along the rim of the sink. The granite company cut the sink the way they prefer instead of the way the sink manufacturer specified. This left a small 1/16" to 1/8" granite overhang and the accessories could not be used. To fix the problem the sink area had to be tented off, exhaust fans installed in the tent, the sink removed, and the granite cut to the specified opening size. It was a real mess doing this in a nearly finished kitchen. The granite company was not happy but acknowledged that they had been warned to not do what they did. They like to leave a little ledge so that they have some tolerance to play with when installing the sink.

Bob Grier
06-21-2018, 3:47 PM
I failed to address the question. Sorry. I do not have a sanitary problem but I also think the way sinks should be installed is as Dan Friedrichs says he sees them. There is no reason the granite can't be cut to match the sink. It might be a good idea to give the sink or a template to the granite people with instructions to cut the granite to match.

Brian Elfert
06-21-2018, 8:19 PM
I have quartz counters with undermount sink. There is a lip about 1/8" or 3/16" wide around the edge. I always thought the lip was to help make sure water got into the sink.

I have only seen the integrated solid surface sinks with solid surface counters.

Curt Harms
06-21-2018, 8:43 PM
I have quartz counters with undermount sink. There is a lip about 1/8" or 3/16" wide around the edge. I always thought the lip was to help make sure water got into the sink.

I have only seen the integrated solid surface sinks with solid surface counters.

I don't know how one would make a stainless sink mounted under a stone counter as smooth as solid surface. We have a solid surface counter with integral sink. This was a DIY project and I made a plywood template to cut the opening slightly undersized then bought a large flush trim bit to flush the countertop opening to the sink. Follow up with a large roundover bit and the sink/countertop joint is absolutely seamless. The downside would be is if for some reason we wanted to change the sink. I'm told it's possible to separate the sink from the countertop but I suspect it would be neither easy nor cheap.

Dave Zellers
06-21-2018, 8:53 PM
I failed to address the question. Sorry. I do not have a sanitary problem but I also think the way sinks should be installed is as Dan Friedrichs says he sees them. There is no reason the granite can't be cut to match the sink. It might be a good idea to give the sink or a template to the granite people with instructions to cut the granite to match.

Well with a SS sink, there is going to be a transition with the counter top. Usually you allow a small overhang to hide the seam and caulk it as has been mentioned.

The one piece counter and sink is awesome but expensive and limited in sizes. And some don't want a Corian or other man made sink because it can scratch and wear and then become hard to clean.

Curt Harms
06-22-2018, 6:53 AM
Well with a SS sink, there is going to be a transition with the counter top. Usually you allow a small overhang to hide the seam and caulk it as has been mentioned.

The one piece counter and sink is awesome but expensive and limited in sizes. And some don't want a Corian or other man made sink because it can scratch and wear and then become hard to clean.

Corian at least can also be sanded back to near new condition. Changing the style or color, well that's another discussion.

roger wiegand
06-22-2018, 8:17 AM
Yes, there's often a crevice in there that is hard to clean or filled with caulk and ugly. I use a brush on ours when I think about it and keep the black stuff that grows there under control. An undermount sink wouldn't be legal in a commercial kitchen in most places because of the gap. I don't worry about it very much and clean as necessary.

Frank Pratt
06-22-2018, 12:45 PM
I've done 4 under mounted stainless steel sinks & all 4 have the counter cutout slightly larger than the sink. That leaves a small (about 1/8") ledge of exposed stainless around the perimeter that is super easy to wipe clean. I used epoxy tinted to match the color of the counter material to secure the sink. Wiping up the rim with a xylene soaked rag cleans up the epoxy line so it's smooth & just barely visible. The tinting probably isn't even needed.

The oldest one is about 10 years old & has had no issues. And when the adult (the men are slobs) children visit I don't have to worry about what they've left behind.

matteo furbacchione
06-23-2018, 11:02 PM
The concept of under-mount sinks is a great one except for the way in which they are stuck to the top. Silicone, no exceptions, will break down and come unstuck from the sink and or the counter top creating gaps of varying widths. Those gaps overtime will fill with moisture and organic material, which in turn will facilitate the growth of moulds. They are very difficult to impossible to clean. And trying to reseal is also nearly impossible to do right. Top mount sinks also have similar problems but can be slightly lifted, cleaned and fixed quite easily and they also, if installed right, have a gasket that seals them quite well. If I were going to go with a composite or stone top, and chose not to have a top mount sink, I'd have an incorporated basin to eliminate the silicone seam.

Ted Calver
06-24-2018, 10:10 AM
The concept of under-mount sinks is a great one except for the way in which they are stuck to the top. Silicone, no exceptions, will break down and come unstuck from the sink and or the counter top creating gaps of varying widths. Those gaps overtime will fill with moisture and organic material, which in turn will facilitate the growth of moulds. They are very difficult to impossible to clean. ....

Exactly what is happening to our 12 year old under-mount SS sink. Looks like a major job to make it right again. It's the silicone. I haven't found one yet that doesn't foster mold growth. The seal around the shower stall doors is silicone and mold loves it. There must be something better.

Frank Pratt
06-24-2018, 12:31 PM
I agree about the silicone & this being a terrible application for it. That's why I came up with the epoxy method.

greg Forster
06-24-2018, 7:59 PM
Ive had plumbing inspectors fail
sinks that were not sealed