ForConstructionPros.com

For this particular erosion sink, Gore's concrete mix included white Portland, white marble sand, white marble aggregate and a titanium white pigment from B&J Colorants, so even when he polished the piece the color remained pure white. The sink top was 2 ft. by 3 ft., and the slab 3 in. thick. Gore used C-Grid by TechFab as the only reinforcement, and added plasticizer to the mix to aid in showing the mold's intricate detail. The sink was diamond polished and sealed with a Buddy Rhodes acrylic sealer.

PRETTY HARDFINE CONCRETE
Charlottesville, Va.
www.prettyhard.com

Alexander Kitchin and his business partner and wife Evelyn Tickle own PRETTYHARD Fine Concrete out of Charlottesville, Va., specializing in countertops, furniture, fireplaces, sinks, bathtubs, surrounds and the like. Pretty Hard constructed this glass-embedded, polished concrete hearth for a local architect's family who wanted something dark and sleek, but with a sparkle, for their modern home.

For the 6-ft. by 2-ft., 3-in.-thick hearth, which sits flush on an exposed concrete block base, PRETTYHARD used a custom-designed mix made up of a lightweight aggregate, hand-sifted black river ash, and Portland cement. They used welded wire mesh and a few pieces of rebar for reinforcement, "mainly for the move to the site."

The slab incorporates a dry pigment for color and lots of recycled bottle glass from Heritage Glass. Kitchin points out that when working with glass in concrete, you need to be aware that silica reacts with the concrete during the curing process, producing an expansive gel. He says that during the initial curing process, with proper hydration, the gel doesn't necessarily cause any problems, but if the concrete repeatedly dries out and gets wet again, more expansive gel will form and possibly cause bowing and/or cracking. "We pour our slabs and wrap them up so water cannot leave. We keep them fully hydrated during the curing process," Kitchin says. "We'll diamond grind and wrap it back up again until it's strong enough to polish to the desired finish and seal."

Kitchin points out that this is a lot easier to do on interior pieces. "Utilizing glass or any silica in exterior concrete, where you cannot guarantee a consistent moisture, content poses a whole range of challenges that must be addressed in the design," he says.