A sink that is mounted underneath a countertop is called an undermount sink or undercounter mounted sink. This style of sink often comes with granite, marble and other solid surface countertops. An undermount sink provides the same quality performance that a conventional drop-in sink offers, in addition to other cleaning-related benefits, when installed correctly. However, there are reasons not to use an undermount sink.
Requires a Solid Surface for Installation
An undermount sink can only be installed on a solid surface, such as natural stone. A laminate or tile countertop is not strong enough to support the weight of an undermount sink, and therefore you shouldn't install it on these surfaces. You need to replace the countertops with a solid surface if you want an undermount sink in a kitchen or bathroom, which can add to the expense of renovations.
Creates a Permanent Hole
In order to install an undermount sink a customized hole, corresponding to the sink’s size and shape, must be made in the countertop. Once the hole is made, changing its size to accommodate a different shaped sink in the future is nearly impossible. In addition, if the sink becomes damaged or falls out, finding a replacement sink to fit the exact specifications of the hole is challenging. On the other hand, a hole made for a drop-in sink is not permanent, because it can be modified to accommodate a slightly different sized and shaped sink. Moreover, drop-in sinks come in standard sizes and shapes, which make it easier to replace them.
Undermount sinks generally cost more than drop-in sinks to purchase and install. This is partly because undermount sinks come in a very broad variety of sizes, shapes and materials. Drop-in sinks come in conventional sizes and shapes with limited design choices. Another reason for the price difference is installation. It generally costs more to install an undermount sink than a drop-in sink, because of additional steps needed during the installation process. For example, installers need to take extra care to secure the sink in place, to prevent moisture from getting in between the countertop and sink, and to make certain it can handle the weight that comes with normal use.