How to Expose Aggregate Inside an Integral Sink

Question:
I’ve had great success exposing aggregate on flat countertop surfaces, but how do I expose aggregate inside an integral sink? Are special tools or procedures required to work around curves and inside corners?

Answer:
Exposing aggregate in a concrete countertop, whether the aggregate is stone, glass or some other material, takes effort and time. Generally a very aggressive (low-grit) diamond pad or metal-bond turbo cup is needed to grind away the surface to expose the aggregate. Finer-grit pads are subsequently used to remove grinding marks and to smooth and refine the surface. As you’ve experienced, this process is fairly straightforward for flat countertop surfaces.

Working inside an integral sink is another story altogether. Often the sink’s shape is curved or complex, and access is tight. It may be physically impossible to get an electric polisher inside the sink. And using an aggressive turbo cup is often out of the question because of the sink’s curved surfaces.

A 3-inch-diameter backer pad with an extra-thick foam backer lets a 4- or 5-diamond polishing disc conform to the inside of a curved sink. While any thin, flexible diamond polishing disc will work, discs that have large diamonds, cut aggressively and have large spaces to flush the cuttings out from under the pad face work the fastest. I prefer DX Series Ultra Speed discs, sold by Granite City Tool. These pads last a long time and are particularly aggressive. While not extremely flexible, they will conform to the inside of a curved sink bowl.

An alternative to an electric polisher is to use a pneumatic polisher with a small flexible backer and large aggressive disc. I’ve already talked about the advantages of pneumatic polishers in a prior entry (see Pneumatic vs. Electric Polishers) so I won’t repeat that here. What matters in this case is that pneumatic polishers are much smaller and can often fit down inside a sink.
You can’t use rotary polishers inside all sinks, however. If your sink has corners, round discs won’t fit into them. So either you’re left sanding by hand, or you don’t expose the aggregate at all. Sometimes there are no easy answers for sinks like this.

It’s possible to expose aggregate inside a curved sink basin, but you’ll need some special tools.

A 3-inch-diameter backer pad with an extra-thick foam backer.

DX Series Ultra Speed discs.

A pneumatic polisher.

Combining the pneumatic polisher with the small flexible backer and 4- to 5-inch diamond disc will allow you to maneuver inside a sink basin.

If your sink has corners, round discs won’t work. To expose the aggregate, you’ll have to sand by hand.