Just as I was racking my brain to remember where I had heard about "rusting" concrete, my eyes hit your column. I hope you know what it is one puts on concrete (something with iron?) that produces rust stains. Help! Thank you.

My wife has been after me for some time to "rust" our backyard concrete patio. The process you are referring to is "acid staining" and can be achieved on both interior and exterior concrete. This trend has been around for about 15 years, primarily in the industrial market, but thanks to the many new home-improvement and decorating TV shows, the fad has been coming on strong in the residential market in the last three years.

This coloring process involves a chemical reaction on a cementitious surface. The solution (water, acid, and inorganic salts) applied to the surface reacts with the minerals present in concrete to create beautiful earth-tone browns, reddish browns, and greens. By mixing and matching available colors and applying them at different rates, you can create your own shades.

It's an art similar to faux painting in that it takes some practice. Not every concrete floor is suitable for the process, for example, exposed aggregate concrete would not be a candidate. An attractive marble-like finish can be achieved easier on a smooth surface rather than on a rough, worn-out one.

You can also score the surface with a diamond blade for a simple "tile" design to which colored grout can be added—score lines provide a natural barrier between colors.

Alternatively, you can create more complex designs using stencils and sandblasting. Acid stain is applied using assorted sprayers and brushes in a nonuniform way, making sure the entire area is wet. Immediately after this, a brush is used to work the stain into the concrete in a circular motion to add random effects. Because it's a chemical reaction, color may not show right away.

If you are acid staining a large area, consider working in smaller manageable sections. Always allow the process to dry before applying the second coat in the same way. Once this has dried, neutralize the surface with water and baking soda and then rinse with clean water.

For exterior applications, apply two coats of clear sealer. I prefer a product called Super Diamond Clear by RPM. Interior floors should be sealed and/or waxed to protect the stain and add shine and depth.

Because acid is used in this process, I recommend that you hire a pro. Find one in the Yellow Pages under "Concrete Contractors" or "Floor Install, Refinish & Resurface." If you plan to try your hand at it, be sure to wear protective chemical-resistant clothing, gloves, boots and eye protection. Also practice on pre-made 18-inch square smooth-faced concrete slabs available at your local home center.

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C.R.S., Inc. · Spokane, Washington · USA