Q.: While visiting downtown San Francisco recently, we noticed that the concrete sidewalks appeared to have a sparkly substance in them. We really like this effect. Can you help us identify the substance and tell us how it can be made available to us? Is this substance compatible with epoxy poly-pebble systems?
A.: Our investigations indicate that the effect is obtained by using a proprietary product made in San Francisco containing cement and fine-grained silicon carbide (usually 16/36 grit) with or without color pigment. It is normally supplied in 100-pound bags and added at the rate of 0.20 to 0.25 pound per square foot of flatwork. In addition, a factory-blended color hardener may be included at the rate of about 0.50 pound per square foot though pastel-colored materials such as light greens and buffs require 0.60 to 0.75 pound per square foot to be effective. The manufacturer's instructions call for applying the product as a dust-on shake after leveling and screeding and before bleeding starts. It is lightly worked into the surface by float. On large areas this can be done by a power trowel with float shoes attached. Finish troweling is delayed to avoid burying the sparkling grains. For best resistance to freeze-thaw exposures the manufacturer recommends applying a cure-and-seal agent and repeating this application once a year. Normally air-entrained concrete would be used for such exposures, but the company recommends using the cure-and-seal agent whether the concrete is air-entrained or not.
As to your second question, the material is compatible with epoxy-aggregate toppings but it requires a great deal more material to obtain the effect. The manufacturer is Conrad Sovig Company, 35 Gilbert Street, San Francisco, California 94103. There may be other sources but as of now we have not found them.