Undermount sink installation is generally much more difficult than drop-in sink installation, but by following several general steps, the installation process can go smoothly and produce a clean look and strong final product. First, choose either an undermount sink installation kit which includes the sink bowl as well as a pre-cut countertop, or choose the individual components and cut the countertop to the appropriate size. Make sure all surfaces are clean and dry before attempting undermount sink installation, and make sure all the proper tools are present and in working order before beginning the process.
If the countertop is not already installed, turn it upside down so the bottom part that will be hidden from view is facing upward. The first step in undermount sink installation is making sure the surface is prepped for installation, so get rid of any splinters, dirt, dust, grime, or moisture from the surface of the counter as well as from the top of the sink bowl. If you have purchased a kit, the directions included with the kit may specify the next few steps regarding applying caulk and screws. If the directions do not give any indication of the process, don't worry: it is not difficult, but it will take a bit of good judgment.
Start by applying a bead of caulk all the way around the lip of the sink bowl for proper undermount sink installation. Make sure to apply a fair amount of caulk, but not enough that it will ooze out and make a mess. Even if it does, don't worry; the caulk can be cleaned up if done so in a timely manner before it sets. Once the caulk is applied, turn the entire sink bowl over and line it up with the hole in the countertop. Make sure the alignment is perfect before taking any more steps. Once screws are installed and the caulk sets, it will be very difficult to make changes to the position of the sink bowl.
Once the bowl is aligned properly, install screws in the provided holes. This will permanently secure the bowl in place, so double check the bowl placement before installing the screws. At this point, it may be helpful to install basic piping, such as pipe elbows that may be difficult to install once the countertop is flipped over and installed. When the countertop is flipped right side up, check the alignment and caulk work before permanently installing the countertop.