# attaching undermount sink



## Daniel Holzman (Mar 10, 2009)

I have put in several undermount sinks in granite. In each case, the granite was drilled and tapped by the granite fabricator, and accepted a stainless steel screw that held a clip in place. Perhaps you can install using adhesive only, I have not seen it done.


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## tns1 (Jun 26, 2009)

The installer did not place inserts. Instead he mounted two wood rails in the cabinet to support the sink and then caulked the sink & cabinet and laid the granite on top. It seems very solid.


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## oh'mike (Sep 18, 2009)

I don't like that sort of install--I've seen it many times and most times it works well---However,I've seen several failures----

Chances are you are good-----I prefer the clips-----You will see----


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## Live_Oak (Aug 22, 2013)

Mechanical fastening is the preferred method. If you don't have room for clips, then your sink is too large for it's base and you should choose a smaller one.


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## tns1 (Jun 26, 2009)

Three years later, and no problems with this type of install. The method the installer used was to attach a 1x3 "rails" to the vertical cabinet panels (3/4 plywood) on each side of the sink. Since the sink just barely fit between these panels, the rails created plenty of support along the sink edge, and would be as strong as strongest part of the cabinet. The mounting was done so the sink rim sat proud of the plywood top by maybe 1/16". I was concerned that this could "high center" the granite adding stress but the installer seemed to know what he was doing, and it was only a 6ft countertop anyway. The sink was set in the cabinet first, then the granite was placed on top. 

An installer has got to love this since there is no drilling or waiting for epoxy to set. It does seem to take greater care/effort to align the cutout while you are setting the granite, and your framing has to be strong.

I am now making cabinets for a cast iron undermount kitchen sink and plan to do it in a similar way. I plan to router a step into the plywood top for full rim support, plus add framing underneath. My only question is if the sink should be flush with the plywood top or if it should sit proud as the prior installer had done. 

Thoughts?


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## ddawg16 (Aug 15, 2011)

Interesting....

In my case, I have a 3/4" plywood base the granite sits on. I trim the plywood so the sink sits in it. Granite goes on top.


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## 123pugsy (Oct 6, 2012)

tns1 said:


> ......................I plan to router a step into the plywood top for full rim support, plus add framing underneath. My only question is if the sink should be flush with the plywood top or if it should sit proud as the prior installer had done.
> 
> Thoughts?


I did this, and dead flush. The sink is going nowhere. No framing below though.

The installers used silicone. I wouldn't let it sit proud though. The silicone will fill a slight gap.


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## RickMacKay (Mar 23, 2016)

You will need a mechanical fastener--i.e. clips. A bracket might work, but something might happen to it down the road....stranger things have happened. If you rely on just silicone or adhesive, this will happen. To save money, a client hired some hack outfit to install tops and a sink.


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## MTN REMODEL LLC (Sep 11, 2010)

RickMacKay said:


> You will need a mechanical fastener--i.e. clips. A bracket might work, but something might happen to it down the road....stranger things have happened. If you rely on just silicone or adhesive, this will happen. To save money, a client hired some hack outfit to install tops and a sink.


And I've seen clips fail...... 

(I'm personally found of a sturdy designed rail frame system. But I think that many installers are reluctant to take the time and effort to complete that on site.... with each cabinet being different and in effect requiring a somewhat custom system. Rather they defer to universal type clip system. 

Note DAWGY and PUGZY did their own rail sysyem... obviously taking the time to construct it appropriately... I would be much more confident in Dawgs and Pugs system/work....)


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## 123pugsy (Oct 6, 2012)

Here's a pic of mine before the top was dropped on.


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## RickMacKay (Mar 23, 2016)

That system works great, unless of course the sink gets damaged and needs to be replaced .


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## 123pugsy (Oct 6, 2012)

RickMacKay said:


> That system works great, unless of course the sink gets damaged and needs to be replaced .


Lucky for me that I'm a stainless steel sheet metal guy........:wink2:
The repairman lives in the house.

I tell everyone to use the thickest sink they can find. This one is 16 ga so it will take a lot of abuse.


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## MTN REMODEL LLC (Sep 11, 2010)

RickMacKay said:


> That system works great, unless of course the sink gets damaged and needs to be replaced .


Rick..... I would agree.... that's a potential issue.... I've never really had a sink fail.... but I generally have installers (or myself) only minimally caulk/glue down the counter/granite/silestone.... more so if I would want to change out cabinetry in the future...

I still do that... although at my age.... I don't anticipate it being my issue in the future.:wink2:

(I just took out a vanity with a integral corian sink in it, and the cabinet was to be repurposed to a garage. The installers had caulked it in for an earthquake or I don't know what......:vs_mad

*But I think you bring up a great point..*..!!!!!!!! that in many applications, we should pay attention to disassembly if there may be likely changes in the future.

Best


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## 123pugsy (Oct 6, 2012)

Yep. The only way to do something is to be prepared to change out the whole top.


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## tns1 (Jun 26, 2009)

As far as using minimal adhesive, what do you recommend? Since the sink rim would be sealed with silicone, would it be OK to do the granite with a few beads of silicone rather than industrial adhesive?


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## 123pugsy (Oct 6, 2012)

tns1 said:


> As far as using minimal adhesive, what do you recommend? Since the sink rim would be sealed with silicone, would it be OK to do the granite with a few beads of silicone rather than industrial adhesive?


You can lay down silicone on the wood and drop the granite on top.
That will hold it.

Why does your sink look like a drop in?

Did you put a straight edge across to make sure it's not sticking up? This could have disastrous consequences. The granite could crack eventually.
A bit lower than the wood is preferred.


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## tns1 (Jun 26, 2009)

123pugsy said:


> You can lay down silicone on the wood and drop the granite on top.
> That will hold it.
> 
> Why does your sink look like a drop in?
> ...



The sink is a drop-in or "tile-in" type, but I am treating it as an undermount. There is more than enough added support under the plywood lip to guarantee it will never sag. The photo does not show it well, but this cast iron sink sits no higher than the plywood top, but because the sink rim is not perfectly flat the gap for the silicone might be almost zero in one spot but 1/16" at another. Also, all the granite slabs I have seen have a fiberglass netting on the underside. Is this netting normally sanded away in the area where the sink rim would contact? If so, it could add another 1/16" to the gap all around.


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## 123pugsy (Oct 6, 2012)

tns1 said:


> The sink is a drop-in or "tile-in" type, but I am treating it as an undermount. There is more than enough added support under the plywood lip to guarantee it will never sag. The photo does not show it well, but this cast iron sink sits no higher than the plywood top, but because the sink rim is not perfectly flat the gap for the silicone might be almost zero in one spot but 1/16" at another. Also, all the granite slabs I have seen have a fiberglass netting on the underside. Is this netting normally sanded away in the area where the sink rim would contact? If so, it could add another 1/16" to the gap all around.


Don't know. I've only seen quartz and marble.

Give your supplier a call and ask.


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