Undermount sink installation techniques

May 1, 2008
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Stone fabricators are employing a range of techniques for installing undermount sinks, although there are some common products and methods being utilized.


Stone World: What methods/products are fabricators using for undermount sink installation?



Dustin Braudway, SFA, Cape Fear Marble and Tile, Inc., Wilmington, NC: After the sink is laid out, we take a 5-inch Makita grinder and butterfly the stone to about a depth of ½ inch. Then we use lead anchors submerged in flowing polyester. Once the glue is dry, we flat grind the glue off flush with a wet cup wheel. This allows our installers to use a #10 machine screw with a wing nut to tighten or draw the sink clips up to the sink.



Joshua Hopkins, SFA, Albemarle Glass Company Inc., Albemarle, NC: We have a seven-step procedure:

1. Align sink with cutout.

2. Epoxy undermount studs around sink flange.

3. Lower sink and place a 1/8-inch bead of silicone on the sink flange.

4. Pull sink up to granite and align.

5. Wait about 15 minutes for epoxy to cure.

6. Mount clips to studs by means of wingnuts, and silicone inside edge of sink.

7. Apply silicone wedges to inside of cabinet and under sink flange by means of wood screw for extra support.



Linus Modlich, Modlich Stoneworks Inc., Columbus/Cincinnati, OH: Slots for our T-31 sink anchors are done on our CNCs.



Canaan Anderson, Florida Custom Marble, Jacksonville, FL: We make a wood frame in the cabinets for the sink to sit on. Then we silicone the seal.



Mark Mihalik, SFA, Counterparts, LLC, Delaware: We almost exclusively fabricate 3-cm material. For most stone, I like to outline the sink flange and grind tapered slots into the granite. We mount the sink using sink clips, flat head machine bolts, wing nuts and silicone. For softer stone or cast iron sinks, I build a wood frame (or occasionally sink setters) to cradle the sink in place. In my opinion, fastening the sink mechanically is fool proof. I’ve repaired the tap in inserts on my competitors’ jobs too often. I’ve never had a sink fail from mechanical fastening.



Dan Riccolo, Morris Granite Co., Morris, IL: We use T-31 sink anchors here.



Darryl Miller, Acoustical Specialties and Supply, Inc., Baton Rouge, LA: We’re also in favor of mechanical fasteners. We tried the epoxy on bolts and started having failures. Now, it’s back to the T-31 sink anchors.



Stone World: What about specific challenges? What are some of the challenges people are encountering, and how are they being solved?



Dustin Braudway, SFA, Cape Fear Marble and Tile, Inc., Wilmington, NC: Some additional challenges on undermount sinks would be:

1. Owners buying the “all-in-one” sink - oversized sinks that can be used as a drop-in or an undermount sink. These sinks typically take up every bit of the cabinet space, thus leaving a thin sink rail in the rear of the sink.

2. Most of our work is in 3-cm exotic materials. When we began importing and selling more exotics, we had to change how and when we rod stones. We had to look at what stones will be rodded prior to going onto the CNC, and what stones don’t need to be rodded (because there are some really hard exotics). We also had to consider how we handle the stone after the sink hole is cut out (because some exotics are super soft).

3. Another challenge was getting clean .dxf files from manufacturers and suppliers of sinks. When we run into these types of problems, usually someone in the Stone Fabricators Alliance has run that type of sink and has a clean version. If not, then we either digitize the sink or just go to the standard method of cutting and polishing by hand. Either way, the sink is going to get done.



George M. Graff, SFA, Snake River Stone Inc., Nampa, ID: We use sink setters from GranQuartz for cast iron sinks and mechanical fasteners for the rest. I have sandwiched stainless steel sinks, but I am turning mechanical with less problems.



Antonio Almonte, SFA, River City Stone Inc., Winnipeg, Manitoba, Canada: One of the challenges facing fabricators now are oversized sinks (as Dustin noted). These sinks are larger in both width and length. In some situations, the overall size of the sink (lip to lip) is larger than the inside cavity of the cabinet. There is not very much room to put anchors in - if at all. In these situations, we inform the customer of the problem. If the customer is still adamant on using the sink, then we show the customer our route to solving the problem. We use the router on the side cabinets to allow the sink lip to sit on and flush to the top of the cabinet. This is fail-proof, but it would be difficult to remove the sink in the future if needed.

In most situations, using anchors, sink setters or wood bracing would work and are fail-proof. Mechanically set undermounts are a must, in my opinion.



Eli Polite, Delaware: We have a simple and easy method (illustrated above). It takes about one minute per slot or less, and there are no special tools or bits needed. We have never seen it fail.



Dustin Braudway, SFA, Cape Fear Marble and Tile, Inc., Wilmington, NC: That’s exactly the way we do it.

George M. Graff, SFA, Snake River Stone Inc., Nampa, ID: I have to agree about the sinks getting larger. I did one yesterday where I had to use a router on the cabinet just to get it in, and there’s not much stone left after cutting the sink cut-out.



Chris Freeman, SFA, Freeman Granite & Marble Inc., Willows, CA: We use T-31 sink anchors on SS and vanity bowls. On kitchen SS, I screw a cleat to the back of the face frame for the front edge of the sink and catch the back with the slots. On cast and other chunky sinks, you can’t beat sink setters. They are expensive, but make life easy. This type of mounting makes the sink replaceable.



Chris Ash, Floyd Knobs, IN: We use a wood frame with screws going up from the bottom to adjust the sink up and down for alignment. This is the cheapest way I have found that can work on any sink at anytime. There is no need to flip the top back over in the shop for anchors or slots. This can even be done at the time of templating, so the sink hole center is 100%. This also makes these monster sinks easy to lay out in the shop, when you have already had it in place at the template stage.

Slots have been around forever, I agree. And so has wood. We have not had one problem with a wood-supported sink.



Kevin Padden, AZ Stone Consulting, Pinal County, AZ: I prefer using either a wood cradle that I fabricate on site, or the “Under Counter Mounter” that is available from a number of supply companies that specialize in stone tooling. I have been using this type of system for years with no failure. The only sinks that I see that are failing are the ones that have been installed relying on silicone caulk alone to hold the sink to the underside of the stone. (These tend to be installed by “pretend” fabricators that just don’t know any better.)

As for me, I strictly rely on support from underneath to hold the sink up and in place, with a silicone caulk bead being a waterproofing membrane only.

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