Building your own concrete sink and integrated countertop leads up to that moment when you knock off the form and witness your creation. It’s nothing less than thrilling to work on this project upside-down and in reverse, and then see it all emerge as intended.
A perfectly molded concrete sink plus counter is simply the natural result of careful planning. If you build the forms with enough care and pour the concrete to spec, you’ll have a concrete sink molded into its own concrete counter—ready to mount on a bathroom vanity or kitchen base cabinet.
Basics of Making and Pouring a Concrete Sink
You can make a concrete countertop either facing up or down. When you make it facing up, the concrete is poured into a form on top of the sink cabinet. Troweling the top to a glass-smooth finish is difficult.
That’s why pouring the concrete upside-down is best for do-it-yourselfers. The smooth bottom of the form becomes the top of the countertop: no troweling necessary. The forms are built with slick, melamine-surfaced MDF. With a loosening agent added to the melamine, it’s easy to release the concrete from the form.
When making a concrete sink, a sink-shaped mold is added to the countertop form. The lower part of this mold prevents concrete from entering the sink cut-out area. The upper part of the mold will create the sink basin.
A second form of melamine MDF must be built around the sink basin mold. This will allow the concrete to settle in around the basin section.
Source: The Spruce