Deprecated: Assigning the return value of new by reference is deprecated in /home/cci/domains/ on line 58 How To Install Undermount Kitchen Sinks - Tech Talk > Installation - Articles : Concrete Countertops, Institute, Concrete Connections, Raleigh, NC : The Concrete Countertop Institute
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How To Install Undermount Kitchen Sinks

Published by Admin on 2010/8/17 (41515 reads)

Understanding how to install undermount sinks is an extremely important part of creating a high quality countertop. This article covers undermount kitchen sinks. Small bathroom or bar sinks are easier - they typically can be mounted directly to the concrete using the hardware provided with the sink. Kitchen sinks are too heavy to mount directly to the concrete, so special preparations must be made.

Order of Installation

It’s very important to install an undermount kitchen sink before the countertop slabs are set down. Once the countertop slabs are set down, you usually will not be able to fit the sink through the hole, and you won't be able to properly seal between the sink and the underside of the countertop.

 1. First install the sink supports. This article explains 3 different ways to create sink supports.

2. Then set the sink onto the support frame.

3. Apply a generous bead of silicone or siliconized acrylic kitchen and bath caulk around the top of the sink’s flange.

4. Install the adjacent countertop slabs over the sink, sandwiching it between the countertop and the cabinet frame.

 Types of Sink Supports

 For concrete countertops, the concrete should not bear the weight of the sink. Instead, you build a support out of plywood, and the cabinet frame together with the support bear the weight of the sink.

 Commercial Bracket

 The first type of support is a commercial sink bracket sold by granite supply companies. These brackets are designed to be installed onto the cabinet frame. Follow the manufacturer's instructions.

Sink Bracket

 Custom Wood Frame

 The second type of support is a custom made wood frame that mounts to the cabinet walls. The frame supports the sink by its flanges. Always leave some wiggle room between the sink bowl and the cradle so that you can align the sink with the countertop hole.

sink cradle   um sink

 Custom Plywood Shelf

 The third type of support is a sheet of ¾” plywood shelf (yellow, below) that’s cut to fit inside the cabinet. The plywood has a hole cut into it that the undermount sink drops into. The hole in the plywood must be large enough to allow for the sink to be moved to align it with the hole in the countertop. Sometimes it’s useful to rout a roundover along the inside edge of the hole. In addition, it’s important to cut holes for all the plumbing and faucet fixtures that mount to the countertop. The hole in the plywood must be large enough to allow for tools to access the faucet and plumbing hardware.





 It is very important to create a watertight seal between the underside of the countertop and the sink. Take care when applying the silicone caulk along the flange of the sink that it is generous enough to create a watertight seal, but not so much that it is messy.

 Bare concrete will react with silicone to produce a nasty-looking, oatmeal-like consistency that will ooze out of the sink joint. Therefore, you must seal the underside of your sink openings so that only sealed concrete touches the silicone.


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