An undermount basin is a sink type that attaches beneath the countertop. Standard sinks are dropped into a hole in the counter and have an edge or lip that helps hold them in place. An undermount basin is generally secured beneath the counter with clips and epoxy instead. Undermount sinks can usually be found in as many different varieties as top-mount sinks. There are many available options in different materials, sizes, styles and shapes.
An undermount basin can be found in an assortment of sizes. Most bathroom sink styles have one bowl, and are usually in a material like copper, granite or colored porcelain. Kitchen sinks are also commonly made from these materials, as well as stainless steel or cast iron. The sinks can be round, oval, square, rectangular or other common shapes. Unusual and irregular designs can be found in some stores, as well.
Undermount basins also come in many different styles. One-bowl and standard double-bowl basins are the most common. Double basins with a three-quarter sized second basin are another option. These can help save counter space in smaller kitchens when the homeowner still wants the convenience of two sinks. Some designs have two basins that are set far enough apart to allow a strip of countertop to separate them, for a truly built-in look. In addition to common shapes and sizes, custom sinks can be purchased from some manufacturers.
While an unusually shaped or custom sink can be a great accent for a kitchen or bathroom, the difficulty of sink installation should be considered. Cutting a hole in the countertop for an irregular-shaped undermount basin is typically more challenging, because there is so little room for error. A drop-in sink hides the cut edge of the counter, but the edge will show with an undermount basin. This makes it necessary for the cut to be more precise, which might require professional help. The counter should also be a solid surface material, since the cut edge will show and be exposed to water.
A double-bowl undermount sink filled with water can weigh well over 100 pounds (45 kg), depending on the size of the sink. Professional sink mounting can help ensure that the sink stays in place properly and does not leak. The precision of the cut that is required, as well as the proper smoothing and cleaning of the material before installation, may be best done by an expert. It also might be necessary to have a plumber or contractor handle the kitchen or bathroom upgrade if the plumbing beneath the sink needs to be changed to accommodate a change in basin size or shape.