How To Install Undermount Sinks: Stainless Steel, Stone, & Porcelain
Follow the steps above, but in place of the solid surface adhesive use 100% silicone (often labeled silicone sealant or silicone caulk) and metal sink mounting brackets. Glue the metal sink mounting brackets to the underside of the top and clamp the bowl in place. Leave the sink brackets in place after the silicone sets for extra support. This type of sink mounting bracket doesn’t require drilling or inserts.
The next step is to remove the countertop material from within the bowl. Before gluing the bowl, place a strip of tape ¼” down from the inside top edge of the sink. This is to protect against any markings that might be left by the nylon bearing as it runs against the surface. Once the bowl is taped and glued in place, use the Straight-Flute router bit (as above) to remove the excess countertop material. This will leave the edge of the countertop nearly flush with the inside of the sink or extend it beyond the edge of the sink by a small amount. You can control how far the top extends into the sink opening by changing the size of the nylon bearing.
If you aren’t comfortable with this approach you can create a plywood template. Most manufacturers supply a template pattern, but it may not allow for the overhang. If they didn’t include one with the purchase of the sink, you can create one out of cardboard that provides the correct overhang and use it to cut an opening in the piece of plywood. Make sure the plywood template has the correct shape and has smooth edges for the top mounted bearing on the router to run against. You are now ready to position the template and make the router cut.
The last step for installing a stainless steel, granite, or porcelain undermount sink is to create the round over for the edge of the top. A small radius Roundover bit is used to create the round top edge. Alternatively, if the edge is left square, a slight rounding can be done with a sander or sanding block. Figure 15 shows three undermount configuration options for the top overhang, including a rounding option.