As one of the older more traditional decorative concrete finishes, salt finish concrete is the most popular in nonfreeze/thaw regions around the country. For little additional cost you can add texture to just about any hardscape. With the popularity of decorative concrete and the wide range of decorative finishes available today, salt finish isn't used much currently. But Lance Boyer, owner of Trademark Concrete Systems, Oxnard, Calif., says that they occasionally see the finish specified on plans, adding that it's sometimes specified in areas between feature panels using more expensive decorative finishes. Salt finish is more decorative than broom finished concrete, which is often the alternative consideration. Landscape architects who want concrete to look like concrete tend to specify salt finishes for that reason.
Installing salt finish concrete requires little extra material or equipment—rock salt and a roller to press it into the surface of fresh concrete is it. Sometimes an installation also involves colored concrete using either integral or dry-shake color hardeners. As with most decorative finishes, timing for the installation is critical.
There is little difference about placing and finishing concrete in preparation for a salt finish. During the bull floating operation, care should be taken to remove the lines created by the float. Finishers often finish a slab either with fresnos or with hand trowels to get a smooth finish to record the print of the salt better. Make sure to finish just after the water sheen has disappeared from the surface.
For best results, workers should broadcast salt when the concrete is just beginning its initial setting phase. The stiffness of the concrete should be the same as it would be for stamping patterns or textures. If you push your finger with moderate pressure into the surface it should penetrate approximately ¼ inch at most. Some finishers also gauge timing by lightly pressing the surface to see if concrete paste or color sticks to their finger—proceeding when there is no residue on their finger. Rock salt rated as “coarse” or “extra coarse” are the most popular sizes to use. Because it is broadcasted by hand in a similar way to throwing dry-shake color hardeners, skill is required by the worker to achieve an even distribution. Having good access around the work area also is important so broadcasting is limited to 15 or 20 lineal feet.
The easiest way to imprint salt texture is with a salt roller. The roller is approximately 3 feet wide, 6 inches in diameter, and weighs 40 pounds. The same extension handles that bull floats employ are used and cost about $100 at construction supply stores. Finishers also use hand floats to tap salt into slab edges and harder to reach areas. The process starts when the edges of the roller or hand float no longer leave marks on the surface. To achieve the best look, press the salt crystals approximately half their diameter into the surface.
After the imprinting is complete, the salt is left in place until the slab can be walked on. Then it is swept or power washed from the surface and the work is completed with an application of sealer.
Salt finishes are unforgiving in one respect. There is little you can do to repair mistakes during or after an installation. Marks left by a roller tend to be permanent and timing is crucial. When salt is pressed too deep or too shallow there's nothing that can be done about it afterward. Boyer also cautions that owner expectations rise with decorative finishes and they tend to be more critical than they would with standard broom finished concrete so you should consider this risk factor when you price the work.