# Undermount Sink - Amount Lip Overhang



## dw85745 (Aug 9, 2014)

I'm doing an oval undermount bowl and wondered:

1) What the "standard" overhang (lip) distance should be from the bowl edge to the edge of the counter top oval opening? 

2) Whether a "drip edge" need to be routed into the underside of the counter top between the bowl edge and the edge of the countertop oval opening so that if water gets underneath it drips off before it hits the bowl edge i-- if so, depth and width of cut appreciated?


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## Steve Neul (Sep 2, 2011)

dw85745 said:


> I'm doing an oval undermount bowl and wondered:
> 
> 1) What the "standard" overhang (lip) distance should be from the bowl edge to the edge of the counter top oval opening?
> 
> 2) Whether a "drip edge" need to be routed into the underside of the counter top between the bowl edge and the edge of the countertop oval opening so that if water gets underneath it drips off before it hits the bowl edge i-- if so, depth and width of cut appreciated?


What kind of counter is it? Normally they are a natural stone material or something like cultured marble where it doesn't hurt anything for water to get to the edge before it gets to the bowl. If it's formica you would be better off with a top-mount bowl. There would be no real way to keep water out of it. I don't know if there is a standard overhang. It would vary depending on how the sink was made. 

You don't need to route a lip, the sink just glues on the underside of the cabinet with an polyester adhesive. It can also be done with a silicone adhesive however I've seen them come loose. To be on the safe side better make a wooden bracket to screw to the underside of the counter to hold the weight.


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## dw85745 (Aug 9, 2014)

Mr. Neul:

Counter top is Corian. Bowl is porcelain. 
While I agree water on underside won't hurt counter top, I do want an overhang to try and keep water from deteriorating the bowl seal. I was looking at between 1/2 and 3/4 inch. But thought -- like a outside window sill -- a drip point underneath might be of benefit.

Will check into "polyester adhesive" -- not familiar with it -- had planned to use silicone as a seal but not for mounting.


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## Trav (May 30, 2011)

I leave an 1/8 of an inch. This leaves a little bit of wiggle room. If the top is natural stone, There is also no way I would mount it with anything other than silicon. Be sure and polish the underside of the stone at least up to a 200 pad. Clean both the underside of the stone and the sink with denatured alcohol and let it dry. Apply a bead of silicon to the rim of the sink then pull it tight to the stone with a bar clamp. Let it dry over night. 

I would stand in any of the 1,000 or so sinks I have installed with silicon.


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## Steve Neul (Sep 2, 2011)

If you can buy it you could also use Corian joint adhesive. Some time ago they made a rule only certified fabricators could buy the Corian sheets but I don't know if that applies to the Joint adhesive. The joint adhesive is the same material as the Corian. Both the Corian and bowl would need to be roughened a little. This would also apply to the polyester adhesive. The polyester adhesive is what the granite people are installing the stone to the cabinet and the undermount sinks to the stone. Its a thick paste which mixes kinda like bondo but hardens hard as a rock. 

Not long ago I had a customer that had a stainless sink once mounted under a granite top. When I saw it, it had come completely loose and hanging. It had been installed with silicone. I cleaned as much of it off as I could and re-installed it with silicone again however after it dried I went in and installed 2x4's all the way around the sides of the cabinet under the sink to prevent it from coming apart again.


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## Trav (May 30, 2011)

You do not want to leave that much over hang. How much water do you expect to come from the counter top into the sink bowl anyway? If you put much more than 1/4" you will find that it will actually cause moisture to accumulate in the corner and promote mild/algae growth. 

Build a frame to support the sink, if you have a pocket hole jig this is a perfect place to use it, use silicon to adhere it to the corian. This is what I do for a living. If the silicon failed on Steve's job it was improperly installed.


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## dw85745 (Aug 9, 2014)

Thanks both for input:



> Corian joint adhesive


Your right still tough to get, but you can get it. Super glue works just aswell.
Had this material left over from a bath I did years ago. Finally found a use for it. At that time used a one piece top with sink so didn't have to deal with this issue.



> 1/8 to 1/4 inch.


Was going on what I thought i remembered from being in restaurant lavatories. 



> If you put much more than 1/4" you will find that it actually cause moisture ... and promote algae growth.


I had given that a thought and was part of the reason I posted the question.
(In your part of the country -- which I always enjoyed -- may be more of a consideration than Arizona.)

-------------

Sink comes with under mount brackets, however Corian recommends glue on -- or -- using heli coil if
screwed to underside. Thought I try and find some glue on supports. If not will go the heli coil route. Also like the silicon better than then polyester adhesive. From my readings based on your post, it sets up 'hard" which would leave little flex if needed for whatever reason.


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## 2lim (Aug 30, 2009)

Every undermount sink that I have come across(that is MANY considering I work almost entirely with new home builders) has been epoxy glued(polyester) at 4-6 points around the the bowl, and the remainder siliconed on to seal. The polyester glue is designed for just this purpose, as well as gluing granite/cultured stone/etc components together. I would highly recommend that you go that route.

Simon


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## dw85745 (Aug 9, 2014)

I just read on article and I may have things backward.

They talked about a positive reveal as having some of the sink edge showing -- from the counter top you step down to the sink where the sink lip (edge) shows about 1/8 to 1/4 inch.

They referred to what I'm doing -- the sink edge (lip) is completely hidden under the counter top as negative reveal.


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## Trav (May 30, 2011)

2lim said:


> Every undermount sink that I have come across(that is MANY considering I work almost entirely with new home builders) has been epoxy glued(polyester) at 4-6 points around the the bowl, and the remainder siliconed on to seal. The polyester glue is designed for just this purpose, as well as gluing granite/cultured stone/etc components together. I would highly recommend that you go that route. Simon



This is so that they don't have to leave it clamped. The 2 part polyester resin cures in around 20 minuets and serves the purpose of the clamp, holds the bowl in place till the silicon sets.


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## Trav (May 30, 2011)

dw85745 said:


> They referred to what I'm doing -- the sink edge (lip) is completely hidden under the counter top as negative reveal.


If you install with a negative reveal it will afford you the opportunity to rework the edge if it is damaged. This is not true if the sink is proud.


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## dw85745 (Aug 9, 2014)

> If you install with a negative reveal it will afford you the opportunity to rework the edge if it is damaged. This is not true if the sink is proud.


So with a negative reveal do you still suggest 1/8 to 1/4 or something wider?

Another question I have is regarding getting a "perfect" oval template. I made one out of plywood,
cut the oval out with a fine tooth scroll saw, used a file, then some sand paper, but still Not "perfect" -- has a few dips and valleys that I can feel but not see. I know these will show up when the router collar or trim bit rubs against it. Any ideas how to get a better oval template by hand -- (no CNC here) ?


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## Steve Neul (Sep 2, 2011)

The odds of damaging the edge of a Corian countertop is almost zero. The stuff is incredibility tough. Corian is also very easy to work. It cuts and shapes just as easy as if it was wood. You could cut the hole a little smaller than the pattern and finish it up with a router. You could use a bearing trimmer or use a template guide with a router to make a clean hole. The edge then can be sanded and polished out. If you wish to radius the edge of the hole you can route a edge on it as well.


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## dw85745 (Aug 9, 2014)

Mr Neul:

I definitely am using a pattern (template). So, whether a router collar, pattern bit, or trim bit is used, IMO it will follow the pattern (template) -- and -- any imperfections in the pattern will show up in the final result (here oval hole). 

Curious how others make their templates by hand and out of what material for the best results?

If I were doing a lot of this I'd have one milled out of aluminum, but for one oval bathroom sink to many $$$.

Have seen some pics of a couple of oval jigs, but they seem awkward with two sliding axes. Don't know how you would go about controlling the size of the oval from the ones I'm seen. That said, I'm sure the sink is most likely Not a perfect oval anyway -- hence IMO the pattern is the best solution.


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## Steve Neul (Sep 2, 2011)

For what you are doing I would just cut the template out with a jigsaw staying outside the line and sand it down to the line with a 3" spindle sander. As long as you keep the template moving when sanding it will sand smooth and even. If you are using a bearing bit if there is any voids in the plywood template I would bondo the holes. If you don't have a spindle sander harbor freight sells one that would fit on a drill press or hand drill. 

When you make the template lay the sink bowl upside down on the plywood and mark a line. Then measure in from there where you want the cut line. Normally the cut line is nearly flush with the bowl. I'm surprised the bowl doesn't have a pattern printed on the box.

In the end the worst case scenario is you have some imperfection on the cut. If you make the cut nearly flush with the bowl you can just sand and reshape the Corian fixing the imperfection. Often a counter is cut back 1/8" from the bowl so it would look normal.


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## dw85745 (Aug 9, 2014)

> if there is any voids in the plywood template I would bondo the holes.


Good idea. I'm using solid core, but will help if needed.



> If you don't have a spindle sander harbor freight sells one that would fit on a drill press or hand drill.


Don't have one. Didn't know they made one for a drill press. Thanks.



> I'm surprised the bowl doesn't have a pattern printed on the box.


Yes, the bowl came with a pattern inside the box. However generic.
What I did was attach the paper pattern to the top of some cardboard. I then cut a hole smaller then the oval outline from the cardboard. I then marked all my measurements on the cardboard underside (side towards floor) and positioned the bowl on that underside. I then reached through the hole and traced the bowl shape onto the cardboard. I then measured inward (toward the bowl center) 1/4 inch and cut the cardboard along that line. This let me know where the bowl must be positioned in relation to the oval. 

I then had a decision to make as to whether I wanted to go with the perfect oval (per paper) and have a different negative reveal between the bowl edge and the perfect oval, or go with the actual bowl pattern (still with a negative reveal) but have an equal distance from the overhang to the bowl. I opted for the latter.

I then marked my plywood template using this pattern, and as stated previously used a scroll saw to cut out the oval. This and a file afterward gave pretty good results, but even with long strokes of the file, still left a few imperfections in the pattern. Going to HF today to see if the spindle sander may help.


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## Steve Neul (Sep 2, 2011)

dw85745 said:


> Good idea. I'm using solid core, but will help if needed.
> 
> Don't have one. Didn't know they made one for a drill press. Thanks.
> 
> ...


Actually for a drill press it's called a drum sander. http://www.harborfreight.com/4-piece-quick-change-sanding-drum-set-35455.html It does the same function but it doesn't oscillate. The oscillation just saves wear and tear on the paper as it doesn't build up as much friction as the drum sander does. I think the drum sander will do you a good job. I would think filing the template would create an edge that was out of square in spots.


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## FrankC (Aug 24, 2012)

Steve Neul said:


> Actually for a drill press it's called a drum sander. http://www.harborfreight.com/4-piece-quick-change-sanding-drum-set-35455.html It does the same function but it doesn't oscillate. The oscillation just saves wear and tear on the paper as it doesn't build up as much friction as the drum sander does. I think the drum sander will do you a good job. I would think filing the template would create an edge that was out of square in spots.


The larger the diameter of the drum the better in this case.


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## Trav (May 30, 2011)

Steve has it correct, cut outside the line and sand to it. 

Corion however is not super durable and is easily damaged comparatively speaking. Both high pressure laminates and most granite materials are substantially more durable. Try leaving a cigarette in the edge of the corian sink. Ask an installer that has been doing it awhile and you will be hard pressed to find one who hasn't had to make that repair. 


The stuff is great but while it has some advantages over natural stone it also has some areas where if pales in comparison.


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## Steve Neul (Sep 2, 2011)

A pan dropped on a natural stone counter can easily chip it. A cigarette allowed to burn on laminate will destroy the laminate where corian isn't easily chipped and if you leave a cigarette burn on corian you can take your orbital sander and just sand it off and polish out the spot. You could also drill a hole in a corian top and use joint adhesive which is the same material as the corian to fill the hole and polish it out to where it would be very hard to find the spot.


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## jjrbus (Dec 6, 2009)

2lim said:


> Every undermount sink that I have come across(that is MANY considering I work almost entirely with new home builders) has been epoxy glued(polyester) at 4-6 points around the the bowl, and the remainder siliconed on to seal. The polyester glue is designed for just this purpose, as well as gluing granite/cultured stone/etc components together. I would highly recommend that you go that route.
> 
> Simon


In my limited experience because "that is the way many new home builders do it" does not make it right or best way! JIm


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## dw85745 (Aug 9, 2014)

Thanks all for input and advice to date.

This is my second go with Corian. The first was back in the late 80's to do a bathroom in my house. Used Corian's one piece vanity w/ bowl at that time so only had to do the side and back splashes. Also did the tub surround (1/4) which I overlaid with 3/4 inch rabbited on top of the 1/4 to make a picture frame around the tub surround. No splicing. Came out nice. What I had left (3/4 and 1/4) I've been carting here and there till now. Just redid my mom's bathroom, and thought a great way to use up this Corian. But been a headache because of:
1) some warping 
2) need to splice the 3/4 because had the length but not the width. 
3) having enough space and the need to construct a flat surface for working area and some jigs. 
4) inability to get materials from Corian so having to do workarounds.

My biggest complaint with Corian is DuPont tight hold on materials. You use to be able to buy 5oz of joint adhesive. Now I believe smallest is 250 ml (50 may still be available), but if your not an "approved" Corian fabriactor you can't get it anyway -- or -- if you can find it, the quantity is prohibitive $$ for a small one-time job. 

FWIW, my favoirte product for the kitchen is laminate, and for the bath, cultured marble or Corian.
Not a fan of granite. In fact my brother-on-law just cut himself on the underside of a granite counter top edge which made quite a cut. Edge was rough textured. But each to his own. There's a price point for everyones budget.


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