Acid Stain Adds Color, Appeal to Concrete

Recently, we heard about an attractive floor finish called “acid stain,” which is applied directly over a previously unfinished concrete slab. It’s said to be easy to care for.

Acid stain is not paint or a coating agent. It’s a coloring process involving a chemical reaction on a cementitious material. A solution made with water, acid and inorganic salts reacts with minerals in the concrete. The result of this reaction is color.

It works well on new or old concrete. Acid stain is a durable product if properly protected with sealer or wax, and it can be applied to interior and exterior surfaces.

The appeal of acid stain is that it gives concrete a mottled, variegated, marble-like look. It creates beautiful colors on concrete, mostly earth-tone browns, reddish browns and greens. You can also create your own shades by mixing and matching available colors, or applying them at different rates.

Don’t expect acid stain to be uniform or have an even tone. You’ll get different reactions from slab to slab, and even on the same job you might see different color patterns.

Acid stain can be applied to walks, entrances, driveways, living rooms, bathrooms, patios, high-traffic areas, and even vertically to any cementitious surface. But not every concrete floor is suitable for acid stain.

Although age is not an issue, condition is. A smooth concrete surface will yield more attractive results than an old, worn one. If the concrete is broken, the aggregate (sand or pebbles) is exposed or has previously been acid-etched, the stain might not take and will not achieve the desired look.

Aggregate does not react with the stain--only materials in the concrete paste do. On some applications where the surface is textured, as in stamped concrete or stamped overlays, acid stain provides more depth of color, greater finish choices and a more realistic look to the surface. Don’t be in a hurry to patch cracks; they add interest to the design and finish.

Preparation for acid staining will depend on the condition of the slab. In the case of new concrete, the only thing needed is to allow time for curing (at least four weeks after being poured), and some rinsing and scrubbing. Do not acid wash before acid staining.

For old concrete, a thorough cleaning is necessary. Surface contaminants such as curing agents, glue, sealers, waxes, paint, oil, dirt, water repellents and anything that will prevent stain penetration must be removed. Degrease the floor and check for water absorption.

Water beads indicate the presence of a contaminant and the floor must be treated again until the concrete readily absorbs water. When rinsing and cleaning an interior floor, use a wet vac to avoid runoff and to prevent staining adjacent areas. It is always a good idea to first try a small test area.

Because the stain contains acid, it is dangerous to work with. Extreme caution should be used when working with acid stain. Wear eye protection and rubber gloves, have plenty of ventilation and follow the manufacturer’s directions to the letter.

Acid stain application involves few tools. All that is needed are assorted brushes and sprayers to apply acid stain--1-quart spray bottles and 1-gallon to 2-gallon pump sprayers will do fine. Use equipment with no metal parts. Shake container before use and fill sprayers. Apply in a nonuniform way, making sure you wet the entire area and follow up immediately with a brush. Using the brush, work the stain into the concrete in a circular motion to add to the random effect.

Varying degrees of fizzing will occur in different areas, and color might not show right away. The process involves a chemical reaction and some colors react slower than others. Apply throughout the entire area. Let the stain dry and then apply a second coat in the same manner.

If you plan to create a design or pattern, you’ll need a saw with a diamond blade in it for scoring the surface. Score lines add a new dimension to acid stain; they provide a natural barrier between colors and create more eye-catching designs.

Use a 4-inch and 7-inch saw with diamond blades. Mark the lines with chalk, and cut to a depth of about one-quarter inch, being careful not to over-cut corners or to miss the lines. Use the 4-inch saw for small detail and the larger saw for long, straight lines.

After the acid stain has dried, the surface must be scrubbed and neutralized. Using a medium-stiffness brush, apply a mixture of water and baking soda to the surface and gently brush the entire area. Rinse thoroughly with clean water.

Once the floor is completely dry, apply two coats of clear non-yellowing sealer and/or wax. Consult your supplier about types of sealer to use for interior or exterior applications and for instructions on how and when to apply wax.

The decorative concrete busi- ness has been growing rapidly over the last few years, and acid stain has been a big part of this growth. More contractors are learning to apply it, and more homeowners, architects and designers are asking for it.

For more home improvement tips and information visit www.onthehouse.com. Readers can mail questions to On the House, APNewsFeatures, 50 Rockefeller Plaza, New York, NY 10020, or e-mail Carey bro@onthehouse.com.