Things You'll Need
This project is best done with at least two people working together. Two individuals can better center the sink into the opening in the countertop and reduce the chance of either one becoming injured.
Installing a sink in a pre-existing granite countertop is not as complex as it may seem. Granite is a durable surface, especially if it is also sealed during the manufacturing process. Several issues need to be kept in mind when dealing with granite countertops, however. This heavy stone is more difficult to cut for the non-pro than composite materials, other man-made surfaces and even concrete. If the granite in your countertop is dark, avoid light-colored adhesives and sealants whenever possible. If they must be used, be vigilant that residues are wiped away as soon as possible to avoid staining the stone. This project involves installing a sink into an existing granite countertop that has been already cut to receive a sink. In this situation, hiring a professional is usually not necessary. The most important thing to remember in any do-it-yourself project is to keep the task as simple as possible while ensuring high-quality and professional-looking results. For this project, that means searching for a "drop-in" style sink at your local home improvement center. Models that are mounted beneath the sink can be used, but they take more time, involve a longer (usually professional) installation, and are harder for a homeowner to install. Here are step-by-step instructions for installing a sink in your granite countertop with a minimum of difficulty.
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Carefully measure the sink opening in your granite countertop. Once installed, the sink will typically take up about 33-by-22 inches from the outside rims. Write these dimensions on a notepad and take this information to your local home improvement center to select your new sink. Be sure to specify that you are interested in a top-mounted (or "self-rimmed") sink because your granite countertop is already installed and the opening has already been cut.
Purchase your sink and position it near the granite countertop. Apply polyurethane sealant to the "lip" beneath the edges of the sink. Keep in mind that unsealed stone absorbs stains easier and presents more of a challenge to clean. If this describes your counter, select sealants and caulking specially designed for this type of stone. It will be easier to apply the polyurethane if the sink is turned over and held tilted at an angle while you do this. If possible, ask another person to hold the sink on one side, lifting it on one end. The rest of it can remain on the floor while you apply the sealant. The two of you can flip the sink carefully back over and bring it up and over the countertop.
Center the sink and carefully lower it into the opening. Take care not to damage or chip the granite when placing the sink. Attach the sink to the plumbing under the cabinet according to the manufacturer's instructions. Make sure that you remember to caulk around all threaded connections to create a waterproof seal.
Place silicone caulk beneath the cabinets on the rim of the sink under the counter where it attaches. This area is called the flange. Use clear, or nearly clear, caulking with your granite countertop, especially if the stone is dark. This will be more important above the sink than below and will give a more professional appearance to the finished project.
Apply pressure on the sink from the top around the edges with your hands to press out any trapped air and ensure a tight seal. Permit the sealant and caulk to dry in place around the sink. Immediately use a cloth to clean any sealant or caulk that shows around the edges of the top of the sink.