Caulking an Undermount Sink in Place
Learn how to affix an undermount sink using a strong silicone-caulk.
I needed to affix a stainless-steel undermount sink to a granite counter that was already installed on its cabinet bases. One of the problems presented by the situation was how to get a good silicone-caulk seal between the underside of the counter and the rim of the sink. Rather than rely on a bunch of braces and shims to wedge the sink in place, I used rope and a couple of wood blocks.
As shown in the drawing, I placed a wood cross brace over each bowl of the sink. Then I threaded a length of small-diameter rope around each brace and through the drain holes. On the underside of the sink, the rope runs through a wood block under each drain tailpiece.
After running a bead of silicone around the rim of the sink, I rotated each block, shortening the ropes and drawing the sink upward with even pressure exerted around the entire rim. The resulting joint is so strong it almost makes the mechanical fasteners redundant.
— Andrew Sheppard; Madison, CT
From Fine Homebuilding #170
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Brilliant approach!
Fasteners probably are redundant. Aquariums are constructed using nothing but silicon, and they hold more water than that sink will.
Ya well aquariums don't hold a disposer, in addition to 300 lb.s worth of cast iron pots, and pans. All relying on only the rim of the sink to hold it to the counter. That's like comparing apples to walnuts.
I think this is a fully functional idea. I am somewhat confused by a couple of the responses however, as no mention in the process was made to claim ability to support "Aquariums"
The resulting joint is so strong it **almost** makes the mechanical fasteners redundant.
As the author suggests, belt & suspenders is always a good idea in situations like this.
All we need now is an easy way to add mechanical fasteners to granite...
Interesting that the FHB editors put another approach to positioning sinks in the same story- check out the tag line "Make a Plumbing Job Easier with a Third Hand" ( https://www.finehomebuilding.com/2021/09/14/third-hand ) I like the 3rd Hand approach better, if for no other reason than you can work from above the counter. That gives you a good view of where the sink is going, which makes the all-important alignment a lot easier.
I have done this using pump clamps on the wooden braces, but not rope. I am curious what keeps the ropes blocks from spinning back loose, perhaps friction but doesn't seem like there would be much friction on a stainless steel sink.