Q.: I need some information about the application of carborundum chips to walks or driveways and the type of company that sells this product. I have a customer who wants this done on a new home he is building.

A.: ACI 302.1R-80, "Guide for Concrete Floor and Slab Construction," Section, mentions the use of emery as a slip-resistant aggregate, and in its Sections 7.12.1 and 7.12.2 it describes how to apply them. The method is much like the method described in the article on page 285 of the March issue, "Dry Shake Hardeners." If Carborundum were to be used instead of emery it would be applied in the same way.

Carborundum is harder and more abrasive than emery. We do not recall hearing of it ever being used for slip resistance--perhaps because emery is generally considered adequate and probably less expensive. Another way to achieve slip resistance is to broom the surface. After final troweling, a push broom--or even a stiff-bristle broom--is drawn over the surface. On most sidewalk or driveway jobs the troweling is omitted entirely to avoid introducing slipperiness, and then these jobs may or may not be finished by brooming.

If your customer is looking for both slip resistance and a black color, emery would be a way to achieve it. Another way would be to use a black pigment with a broomed surface. Your customer should be warned, however, that black surfaces may not remain a deep black indefinitely because of the tendency for lime and alkalis in the concrete to come to the surface and lighten the color.

Carborundum is manufactured by The Carborundum Company, P.O. Box 337-T, Niagara Falls, New York 14302. Perhaps the company can give you the names of local distributors, or perhaps you could find distributors listed under "Abrasives" in the yellow pages of your local phone book. You would want to buy a relatively coarse grade. Emery and other slip-resistant aggregates are made by a number of manufacturers of floor hardening materials.