Q.: A client of our New Jersey architectural firm wants to use a rock-salt texture for the concrete deck of her swimming pool. We're not familiar with this process and wondered how the effect is achieved.
A.: The texture is produced by scattering rock salt over the surface after floating. The finisher presses the salt grains into the surface with a float or roller, leaving only the tops exposed. After curing the slab for seven days under waterproof paper, workers wash and brush the surface, leaving pits or holes from the dislodged or dissolved salt grains.
A slightly different procedure is described in the Problem Clinic article Producing a Rock-salt Finish in Concrete Construction, May 1995, page 475.
A rock-salt finish isn't recommended for use in areas subject to freezing weather because water trapped in the holes tends to spall the surface when frozen. A more detailed account of the finishing process is provided in the Portland Cement Association publication Color and Texture in Architectural Concrete. You may order this book online or call the Aberdeen Bookstore at 800-323-3550.