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April 2010 Vol. 10 No. 3
Feature Article
Seeding FloorsPlace decorative aggregate by hand instead of mixing it inby Sue Marquette Poremba  Traditionally, seeding was simple. It meant scattering pieces of rock into the surface of concrete, where they would give decorative flair to a slab. "Nowadays, seeding has taken on a broader realm," says Tom Ralston, CEO of Tom Ralston Concrete, in Santa Cruz, Calif. "We seed glass bits, silicon carbide, sometimes even bits of metal. Different things can be seeded - or broadcast - into the concrete, later to be exposed."  Seeding helps create unique looks that aren't obtainable with other materials, explains Bob Harris, president of the Decorative Concrete Institute. "There are thousands of options available, when you consider tinting the matrix of your ready-mixed concrete or cement-based topping with a variety of colors as a base into which you can seed exotic aggregates."
One reason contractors might seed concrete rather than adding decorative aggregate to the mix before pouring or casting is the overall cost. "You could be adding 2,500 pounds of aggregate, and aggregate can run 10 cents to 20 cents a pound," says Tim Blankenship, concrete specialist at Blankenship Concrete Specialties. "You could end up adding a couple hundred more dollars per yard to your concrete costs just from the aggregate." Rather than adding a couple thousand pounds of aggregate into the mix, you can add six pounds of aggregate to the surface and get close to the same look, he says. "For example, we did a project several years ago where they wanted the aggregate in the mix. The cost when installed was around $14 a square foot. Had we broadcast the aggregate, it would have cost between $7 and $9 a square foot." Other considerations include...
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