How do we convert our drop-in sink to an undermount one?

Question

We are in the process of remodeling our kitchen and are trying to narrow in on our sink for our new granite counters. We like the Kohler Staccato with unequal bowls and would like to have it undermount. However, there is a HUGE difference in price: drop-in is $250 vs. undercounter is $630. I know that there are some differences between the two, but not $380 worth, and if anything, the undercounter probably has less metal. I'm sure it is a premium tax for the undercounter option.

I ran across this post that mentions that they used converted a drop-in to undermount.

Does anyone know what is involved with that type of change? What are the things I need to be aware of?

Answer 1

Matt, there is a huge difference between an under mount and a drop in fixture. The first concern is the counter itself. what kind are you using? Some counter tops cannot be used with an under mount sink. The support and sealing of an under mount sink is completely different than a drop in. The holes for the faucet need to be in the counter, not the sink unit, and the edges of the sink unit have to be flat and are usually epoxied and clamped in place while the counter is upside down. If you are very clever, you probably can fit the drop in under the counter, but how are you going to finish the counter edges and drill your fixture holes? They will need to be polished. This is usually a production job, not a DIY unless you give the counter maker an exact template, not something you can simply cut out and do yourself.

Answer 2

I think it would be hard to use a drop-in in an undermount installation. There are come sinks that can be used for both, we just got one for our bar sink. You just have to knock out a few holes for the undermount. I don't know why that sink cost so much more however, they are the same depth and the same steel gague. That exact undermount sink is considerably cheaper on build.com however ($536 with free shipping).

Typically with a granite install, the installers will handle the sink for you, so I would talk to them before they come. They may even be able to take the sink back with then after they come out to measure, and before the cut the granite to see if it would work.

You also may want to consider using a Silgranite sink instead of a stainless steel one. This is becoming more and more popular per our granite installer. They are made from a composite granite and polymer mix, and do not scratch like stainless steel, and can match your counter in color. They also do not stain like granite can as they are not porous. The one I mentioned that we just bought for the bar that was over / under mount was a Blanco Silgranite. Looking at the collection, they are cheaper than stanless and have some designes that may match the style you want.

Answer 3

You also need to consider depth -- undermounting your sink may place it a 1-2+ inches lower than it was, and can alter your ability to drain properly (need to have room for things like venting, trap, etc.)

This could be further complicated by whether you will have a garbage-disposal unit mounted below the sink.

How about water filtration? Will you have room for any water filtration systems under the sink? Pre-heating hot-water heaters? Reverse-Osmosis?

Will the extra 1-2+ inches put more strain on your back when you have to lift something out of the bottom of the sink?

I hope these ideas helped...

Answer 4

I had a used drop in sink in Costa Rica and when I remodeled the contractor used a grinder with a metal blade to cut of the wide part of the over mount sink and then installed it as an undercount. When I commented, he said he does it all the time to save his clients lots of money! Looks great and you can’t tell the difference!

Answer 5

I am doing what I call a 'sandwich' mount, which invloves dropping the sink into one thickness unfinished mdf board, securing it in the typical drop-in fashion, then making my own faux stone finish from epoxy on another thickness, making just a slight alteration the mdf where the top layer will sit on the sink rim (1/4 inch higher). This will allow me to 'pour over' the edges with the epoxy on my top layer, giving it a proper finished edge where in the interior rim. Once in place, I will screw the two mdf layers together from below. Also, the bottom layer is cut to FLUSH with the cabinet fronts, and the top layer will have an additional strip of mdf running under any front edges to give me a full thickness of finished, poured-over front edge. So simple,tons of fun making this epoxy counter, and we can use any sink we want. You can only 'sandwich mount' if you are making your own counter, though. And soooo much cheaper and better than the big stores' cheapest laminate or solid-surface counter. My whole kitchen, including an island, is costing me less than $500 including mdf, epoxy and supplies, and the sink.

I came up with this when I realized that drop-in sinks and undermount sinks have more in common than differences. They all have a nice flat rim top, maybe just 1/4 inch more narrow a rim than undermount sinks.

Contact me for pics of this process if I didn't explain it sufficiently.

Answer 6

A drop in sink obviously uses a rough in with the granite. Therefore, the cut where the top installs is unfinished. Most likely, it's jagged and uneven because the lip of the top mount sink will cover it up. Whereas, with the undermount sink requires it to be polished smooth and have straight lines because that's going to be part of the finished look. The labor is much more intensive than it looks plus the tools to do the job properly. There's where most of the extra cost lies in doing the under mount vs top mount.

Answer 7

To be honest I would say if drop in sink's edge surfaces flat, it wouldn't be difficult to install that as under mount, just need few holes under the counter top to tighten the sink to the counter top and rather than using rubber sealer use adhesive type silicone between. I would suggest ask counter top installer guys do it for you,because they have lots of experiences and they know if that certain drop in sink also can be used as under mount.

Answer 8

You take a cutting wheel to the raised edges of the sink and cut it. You'll still be left with enough to support it. The counter people must have the sink ready to measure the opening in the countertop, so you must do this before they come to template the countertop. Then, if granite you can epoxy the sink right to the countertop. If soap stone, you can create some kind of small frame to support the sink and the countertop will just go above it. Like other posters said - the price of undermount is unjustified considering how easy it is to take a top mount sink and convert it into an undermount. The main thing is to have this done before they come to template it. Also have your new faucet ready - they'll need to drill holes into the countertop for it.

Answer 9

I've checked the specification sheets on the two versions of a Kohler Cast Iron sink, and the only difference is not the edge or flange, they are exactly the same, it is the hole diameter sizing. They make them much smaller for top mount so you don't need a large escucheon plate. Plus the faucet mounting hardware may not fit through the small holes of the top mount, once mounted below the granite or stone countertop. It will mount exactly the same, but you will have to really check all the extra hardware and how it mounts through the stone and sink.