Q.: How can we give an existing concrete surface an antiqued finish?
A.: That depends on what you mean by antiqued--here beauty is in the eye of the beholder. The question usually comes up with new concrete surfaces. Existing surfaces may be an even greater challenge, depending on the degree of exposure and extent of contaminants. Experiment with color and texture. Techniques such as scabbling, scarifying, shotblasting, and grinding can clean the surface and expose or fracture aggregates to reveal surface texture. Commercial concrete stains can achieve a range of colors. Check with a specific manufacturer about procedures to produce a mottled, rather than uniform, appearance. We've heard of washing with a solution of carbon black in water to achieve a look of "artificial weathering." You also might consider ferrous sulfate solutions to give a brown or buff color, or copper sulfate to give shades of green. Apply the solution to the concrete surface and let stand for about 15 minutes before washing off. Repeat until the desired effect is achieved.