A Sink For Every Style, Pt 2

The first step in mounting a sink is to master the particular method (or methods) your company uses. Everyone seems to have their particular way of dealing with sinks; here’s a rundown of the techniques I’ve seen in effective mounting.
1. The saw cut diagonal slot. A slot is cut in the bottom of the stone to capture the head of the screw, while allowing the threaded body to pass through. This permits the screw to receive a nut that, in turn, holds the clip that secures the sink to the stone.
This method is the most-inexpensive, and – if the need arises – can be cut in on-site. But, it does come with a few pitfalls.
First, an inexperienced guy cutting the slot can go too deep and slice right through the surface. He can also widen the slot too much, allowing the screw head to simply drop through.
Second, it’s hard to use this method on stone that is sugary or otherwise structurally unsound. Tighten the nut too much, and the stone above the slot will simply blow out, leaving the sink with no support at all in that area – or, worse yet, blowing out a bottom section of your polished sink opening.
2. The expanding lead anchor. A hole is drilled, and a threaded lead anchor (sometimes supplied by the sink manufacturer) is epoxied in place. If you have the technology in your shop to machine a hole to a precise diameter and depth, a lead anchor is a good way to go. These anchors are amazingly strong, even holding up a cast-iron sink.
However, if you have to drill your holes by hand, you might think about a different method. Just blow out the top of a finished undermount sink piece with your drill and you’ll know why. I’ve witnessed that moment firsthand; it’s expensive and not pretty.
3. A threaded T-nut. A slot is cut in the bottom of the stone, and a threaded T-nut is glued in with a structural epoxy. This method works well (I’ve installed hundreds of sinks with it) and the same adhesive used for rodding can be used for the T-nuts.
These mounts are strong, but overtightening the clip against the bottom of the sink can occasionally dislodge these from the bottom of the stone. If you want to try this method, make sure you tape off the bottom of the T-nut before placing it in the epoxied slot; otherwise, you’ll end up with epoxy where your screw should go.
4. Aluminum-bar sink undermounter kits. The top of the cabinet rail is carved out in front and back, and brackets are mounted. An aluminum bar hangs on these brackets with soft-topped threaded machine screws for seating the sink. The screws are spun to raise the sink up to the bottom of the stone.
I’ve used these on at least 50 sinks and have had good luck with them. They work especially well when mounting a small sink inside a large cabinet.
One drawback with them is that they are relatively expensive (over $15 for a pair) in comparison to other methods. Another drawback is that carefully cutting the wood to mount the holding brackets is time-consuming.
Finally, a word of caution with this mounting system: When you spin the screws, it’s possible to overtighten and actually raise the countertop as well. This can be dangerous because you’re then putting a lot of pressure on one spot around the cutout of an undermount sink.
I’ve yet to break a piece using an undermounter kit, but on a couple of occasions I turned the screws too high … and it was just luck that the piece didn’t break.
5. Glued undermount studs. A threaded rod with a flat, perforated base is glued to the bottom of the stone. The sink clip is placed on this rod and held in place by a nut.
With today’s advanced epoxies, this method works well. My favorite is from Chemical Concepts; they also make a fantastic system for mounting dishwashers to the bottom of stone.
To get the best epoxy bond, you need to make sure the surface of the stone is perfectly clean. If there’s dust on the stone, the bond will not withstand the force created by tightening the sink.
The biggest drawback I see with using undermounting studs is the fact that they stick out from the bottom of the piece. I’m a big fan of laying pieces down on cabinet tops and sliding them around as soon as there is enough support. Because of that, I limit my use of these studs to easier pieces like open-ended bath vanities.
That being said, undermounting studs work great as replacement and emergency clips. If you lose a clip because of a stone blowout or drilling a hole, or have a sagging sink section that needs more support, it’s relatively easy to glue one of these in place.
I slide a piece of cardboard over the stud to catch any dripping epoxy, and then shim a piece of wood firmly underneath the stud until the glue dries. The epoxy takes approximately 10 minutes to set, so if you’re using an undermounting stud to firm up a sagging sink, you’d better not waste too much time getting it in place. The adhesive around your sink can do a lot of setting up in a short time period.
6. A T-31 slot. A pneumatic anchor machine (such as the Hercules GG -210 from Braxton Bragg) is used to cut a slot in the bottom of the stone that accepts the head of a 1/4” machine screw to hang the clip. This is my favorite method for mounting sinks for several reasons.
First, once the depth is set on the bit, it’s impossible to run it through the top and ruin a piece. (Keep in mind that, with this machine, you may need to change cutting depth if you change stone thickness.) Second, the machine leaves enough stone that there is no worry of blowing out the bottom of the slot with a tight clip. Third, since it’s only a slot, you never have to worry about anything protruding out of the bottom of the stone (such as a lead anchor or T-nut) and creating a dangerous high spot.
7. Cabinet mounting. Gluing and screwing wood pieces to the sides, front, and back walls of the cabinet, and then setting the sink on them, is sometimes the best way to go; I prefer it with a heavy cast-iron sink.
One important point to remember with a cabinet mount is to leave a little wiggle room. Your boards should catch the rim of the sink, but not crowd the bowl.
If your wood is too tight and the sink cutout is a little off, you may be stuck with a bowl that will not move as far as you need it to. This is a major reversal, and will require the dangerous task of tipping up a sink piece to adapt the wood mount. If you are going to cabinet mount on a regular basis, bring along as many different thicknessess of wood as you can find.
I’m not a purist when it comes to mounting sinks. I mix and match methods on a regular basis to meet the particular job.
Sometimes mounts will be inaccessible, especially in between the front of the bowl and the back of a cabinet rail. Here, I install a piece of wood on the back of the cabinet rail set low enough to slide the rim of the sink over the top without smearing off the caulk bead on top. Once the sink is aligned you can use wood shims to raise it up tight with the bottom of the stone.
Finally, your sink-mounting methods should be all about stability, efficiency and economy. Every fabricator and installer is going to have their own preference, and I’m all about using what’s worked in the past for you. I would encourage you to carefully experiment with different methods, if for no other reason than having the experience to use them if the need arises. In a perfect world, you may find a method that works even better than the one you use now.
Next month, we’ll adhere the sink to the stone, hold it in place while the clips are set, and do a final touch up.
Jason Nottestad, a 12-year stone industry veteran, is co-owner of Wisconsin-based Midwest Template Services (www.countertopsbymts.com)