Q.: We wrote a job specification calling for application of a colored dry shake to 50,000 square feet of concrete floor. The contractor didn't read the specification and finished the concrete without applying the colored dry shake. Workers applied a membrane curing compound to the concrete. Is there any way to color the floor now so it doesn't have to be removed and replaced?
A.: Surface-applied stains can be used to color the concrete, but you won't get as deep a color as you would have achieved with the dry shake. To get the stain to penetrate, the contractor will have to remove the curing compound, either by using chemicals or abrasive blasting. Blasting will alter surface texture, but could open the surface so it accepts the stain more readily.
Regardless of the surface-preparation method used, the color of stained concrete won't be uniform. This nonuniformity is characteristic, and in some installations the softness or patina of the effect is valued.
We suggest that the contractor contact some concrete stain manufacturers, describe the problem and ask about staining options. He might try removing the curing compound in a small area, applying the stain and asking the owner if the resulting color is acceptable. (The curing compound manufacturer can provide information on how to remove the compound most efficiently.) Expect some variation in color over large areas because of batch-to-batch variations in concrete color.