What holds my undermount sink in place? October 2nd, 2009
Most stainless steel undermount sinks are installed underneath granite, marble, concrete, Corian®, Silestone®, quartz or other stone countertops.
There are several ways to install undermount sinks. Most methods are fine but the method used generally depends on the way the installer was trained to do it. Some installers prefer clips or brackets and some prefer the glue in method.
Clips that ship with most undermount sinks
The clips that are shipped with most sinks are simply a strip of metal about an inch long with a hole in one end and a screw and holder which is seated in the stone around the outside of the sink.These work well, but need to be installed at the shop and not at your house. The risk of using this type of clip is that if the fabricator is not experienced or does not have the proper equipment, the stone can become cracked or broken. The hole for the screw is drilled into the stone from the bottom about half way through to insert the plastic for the screw. The metal strip then extends over the edge of the sink and is tightened to hold the sink. There are generally about 10 of these clips around the outside of the sink which means about 10 more holes part way through the stone which can crack during installation or at a later time.
This type of installation also requires additional space around the outside of the sink for the clips which can limit the size of the sink that can fit into the cabinet.
Undermount sink brackets
There are also brackets available to installers that run from the front to the back of the cabinet before installation. These brackets also have screws in the brackets to hold the sink up against the stone from the bottom. There are generally two of these per sink installation. They do require that the installer put two small notches in the cabinet to hold the bracket, one on the front and one on the rear of the cabinet. The notches are not visible in the finished product unless you look from below the level of the cabinet. No additional holes are required in the stone for this type of installation.
The traditional method, glue
The most widely used method of installation is gluing the sink to the stone. This sounds like a poor way of securing the sink, but it actually is works very well. It is also the best method if you ever have to remove the sink. After the countertop is installed and secured, the sink is installed from underneath the countertop.
This type of installation will require a two part epoxy that is used in the solid surface countertop industry to install sinks and glue seams. They will put several portions of the epoxy around the edge of the sink in about six to eight places, and then they will go completely around the edge of the sink where it will contact the stone with clear structural silicon. The silicon will also form the seal between the sink and the countertop. It is important that they use silicon and not latex caulking. The latex will not hold. The stone must also be very dry.
When glued in, the sink is then pulled up from underneath and held in place with clamps through the drain holes and a 2X4 across the countertop. In about 2 hours the clamps can be removed, but the silicon, which is what really holds the sink, needs 24 hours to dry. Do not hang the garbage disposal on the sink during this time.
For additional security often small pieces of stone (about the size of a silver dollar) are glued underneath the sink overlapping the edge of the sink and the stone. These can be knocked off it the sink has to be removed for any reason. Below is a picture of an undermount sink that was installed a long time ago without any mounting hardware. Only glue and a few small fragments of stone hold the sink up.
Sandwiching the sink between plywood and stone
Installers who deck the cabinets with plywood underneath the stone often just clamp the edge of the sink between the decking and the stone. This is a simple installation, but the sink cannot be removed without taking the countertops off.
This represents most of the methods of installing stainless steel undermount sinks. You can discuss this with your fabricator before installation to know how he is going to do yours. The clips described above generally ship with the sink. The brackets do not and will have to be purchased separately. If the installer glues the sink in, he should provide everything that is necessary for the installation.