Undermount Sink Installation Question

[Jeff Wright]

I am designing our kitchen cabs and would like to minimize the width of the sink cabinet. We will be using a double bowl STAINLESS STEEL UNDERMOUNT sink 31.5" long. The mounting hardware that comes with it suggests you need some added space on the sides of the sink and the interior of the cabinet near the side walls to allow the hardware room to be installed. I am trying to gain some added design space to the side of the sink cab and would like to install the sink without having to use those hardware pieces, allowing me to set the sink edge adjacent to the cabinet's side walls.

Question: I noticed today at a kitchen showroom an undermount stainless sink installed with NO hardware but using ONLY a sealant (I suspect a type of silicone caulking). Is it an acceptable practice to install a sink like that and not using the provided hardware? With the weight of a garbage disposal the sink's weight, plus the sink loaded with some water . . . wouldn't the sink be at risk of detaching itself? And if using only an adhesive to mount the sink is acceptable practice, how difficult is it to remove the sink if a time comes to replace it?

[Jamie Buxton]

There's a number of ways to install an undermount sink. One of them is to support the sink with a plywood sub-top underneath the sink. A bead of caulk goes on the rim of the sink to seal it to the underside of the stone slab counter-top. You may seen an installation done like this.

[Ben Franz]

Jeff - I wouldn't trust any adhesive in this application - imagine setting a full stock pot with scalding water in the sink a little too hard as a worst case scenario that could delay Sunday dinner. The solid surface industry does bond their sinks to the countertop with a proprietary adhesive that fuses two identical materials into a single unit. A stainless sink bonded to a stone slab isn't the same.

Jamie's suggestion is a good one. If you are setting stone tops, they need a plywood underlayment anyway. I did many kitchens where I cut out the underlayment to allow the sink bowl(s) to drop in with the flange sitting on the plywood. I would trace the flange outline and then rout a shallow recess to allow the sink to sit flush with the plywood surface or slightly above it. The stone countertop sits on top with a caulk seal. This does make it a little harder to shift the sink if the countertop fabricator is a little bit off on the sink position.

If you don't have plywood underlayment, there are metal rail kits available that have screws or bolts to jack the sink up from below. Either of these methods allow the sink cabinet to be minimal width but in my experience, more room under there is better once you start adding water filters or heaters, gynormous disposers or less than minimal sized contractors trying to hook everything up. DAMHIKT. Good luck.

[Jeff Wright]

Great info and insight; thanks!

The stainless undermount I ordered requires a minimum of 33 inches between the cab's inside walls. I'll design one with about 34 1/2 inches.

Do you know of any good install instructions that show some photos of the ply underlayment using the recessed cut out idea you mentioned?

The sink kit comes with some mounting hardware which I will use in addition to any silicone sealant.

[Ben Franz]

Don't have any instructions - my method was homebrewed. Most sinks come with a template that can be used to cut the through hole in the plywood. This hole doesn't have to be exact - a little wiggle room allows you to fine tune the sink position. Once the sink is in the hole it should be sitting on the plywood, supported by its flange. Just trace around the flange perimeter and rout a shallow recess to lower the sink to be nearly flush with the plywood. This recess also keeps the sink from moving around during countertop installation. Some stainless simks that are designed for ONLY undermount applications have flat flanges that are only the thickness of the sheetmetal. These could be installed without routing a recess but I would still do it for stability. I don't think you'll need the sink HW if you do it this way.

[fRED mCnEILL]

On my sink I glued it in place using silicone but then built some cross braces underneath for added strength. Its been 5 years and no problems. I don't think you want to "trap" the sink beteeen the countertop(stone?) and the cabinet top as you would not be able to remove it should the need arise.

Fred Mc.

[Phil Phelps]

There is a big difference between silicone adhesive and sealant. Many say both adhesive and selant, but I wouldn't use it for an adhesive. Too many products on the market calim to do what they don't. CR Laurance makes a silicone glass adhesive that really works. However, I'd brace that sink so it would never fall out.

[Jamie Buxton]

... I don't think you want to "trap" the sink beteeen the countertop(stone?) and the cabinet top as you would not be able to remove it should the need arise...

I can't conceive of a situation in which the sink might need replacement. The thing is stainless steel. It doesn't rust. It doesn't chip. It has no moving parts. Heck, you can even buff it in place with sandpaper or steel wool.