The oldest methods of adding glitter to concrete are shiny aggregates - mica, glass, bits of mirror and so forth. More recent additives include silica carbide, spar, and "pixie dust" made of small glass beads.
Making concrete sparkle is not as simple as waving a magic wand. Unusual additives and aggregates require specifically formulated mixes to keep them in place.
For example, Bill Kulish, owner of Quintechs LLC in Wilmington, Del., adds VCAS white pozzolan from Ball Consulting Ltd. to a basic countertop mix to increase strength and density and reduce porosity. He also adds Ball's Forton VF-774, which also reduces water and increases strength but has the added benefit of allowing a dry cure, so it is not necessary to keep the surface hydrated for the cement to reach full strength.
The sparkle aggregates are applied next, usually surface-seeded to deliver maximum visual impact. Contractors can give their customers the best outcome by working with suppliers who can provide proven formulations, training, and even licensed systems.
To go beyond concrete aggregates that reflect light to those that actually radiate it, designers are discovering photoluminescent aggregates. Early experiments with a countertop 10 years ago led Peter Tome, founder and president of Ambient Glow Technology (AGT), to develop powerful glow aggregates specifically for decorative concrete, cement, terrazzo, stucco and floor epoxy systems. Available in a variety of colors, AGT aggregates absorb light during the day and glow for more than 12 hours in the dark. They have a life span of more than 20 years, with the brightness diminishing very gradually over that time.
Photoluminescent aggregates in countertops are a friendly feature for people enjoying midnight snacks or making nocturnal trips to the bathroom. They are a great special effect for outdoor bars and patios too. "Everyone that has seen the glowing aggregates is blown away," says Tom Ralston, president of Tom Ralston Concrete, Santa Cruz, Calif. "The first client I showed them to wanted the AGT fine sand dusted on his porch like a galaxy of stars with the constellation of Cancer (his wife's zodiac sign) seeded in larger aggregates."
Photoluminescent aggregates light up more prosaic applications too. "They may find a lasting home in the field of safety," Ralston explains. For example, he has filled saw cuts on stair edges with glow aggregates so the steps would be clearly visible in the dark. Glow aggregates can be stamped into pool decks, used to light stepping stones outside cabins or cottages, or provide ambient light for a path from a beach house to the water.
Some AGT aggregates are as fine as sand and others range from 1/4 inch to 1/2 inch in size. AGT aggregates can be used in both precast and cast-in-place applications, as well as in stamped concrete. The incorporation process is like that with any other exposed aggregate. "Pour your batch, then before hard troweling, hand-broadcast the glow aggregates over the surface. Cover with the cream, and then when cured, grind or polish to expose the aggregates." Tome recommends using recycled glass or other decorative aggregates as well, "so during the day you don't have blah gray concrete. The recycled glass gives it a beautiful aesthetic. Then at night the surface comes alive."