Sandblasting is one of the many methods used to texture the surface of hardened concrete. The degree of blasting may vary from light cleaning to a deep cutting operation that exposes aggregates to a three-fourth of an inch depth of more. Although the actual sandblasting operation is not particularly complicated, certain procedures and precautions should be followed to insure an attractive surface.
The equipment needed for blasting may vary depending on the depth of cut specified. If the surface is to be gone over lightly to remove the surfaces "skin", almost any sandblasting equipment will serve. When the blasting operation is to cut deeper, the capacity of the equipment becomes a matter of considerable importance. Air compressors should have a capacity of about 300 cfm for each nozzle being used. Minimum air pressure at the nozzle should be 90 psi; 100 psi; is preferred. The nozzle should be a venturi type with a minimum inside diameter of three-eighths of an inch. The hose line should have adequate strength for the pressures being used, and the inside diameter of the hose should be no less then one and one-half inches to keep the sand in continuous suspension while traveling through the hose.
The proper time to do the blasting is a question of economics. The concrete matrix will be easier to cut in the first 24 to 72 hours after casting. When blasting a surface, the operator should hold the nozzle perpendicular to the surface and about 2 feet away. The exact distance depends on the pressure being used, the hardness of the concrete matrix, and the cutting ability of the abrasive. An experienced operator can quickly determine the nozzle position to produce the specified surface finish.