Recently, wife Carol told us about an attractive floor finish that she had discovered in a new local eatery. She said the floor was rich looking and was something she hadn't seen before.
Curious, she asked the manager what the finish was. He told her it was "acid stain" applied directly over the previously unfinished concrete slab. In addition, he raved about how easy it is to care for.
This was exactly what she was looking for to replace a section of hardwood floor and a couple of small patches of sheet vinyl in her Day Spa & Salon. The hardwood in question was located below three hair-washing sinks and had sustained repeated water damage over years. The no-wax vinyl, too, had seen better days.
For a replacement, Carol wanted a finish that was attractive, unusual, cost-efficient and easy to care for. In the six months since the finish was installed, the acid stain has met the test on all accounts. She likes the finish so much it soon will replace carpet in other areas of the spa.
Acid stain is not paint or 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 already present in the concrete. The result of this reaction is color. What's more, it works very 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 both interior and exterior surfaces.
What makes acid stain so attractive? Acid stain gives concrete a mottled, variegated, marblelike 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 your available colors, or applying them at different rates. Never 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. However, not every concrete floor is suitable for acid stain. Although age is not an issue, its condition is. A smooth concrete surface will yield more attractive results than will an old worn one. If the concrete is spalled, the aggregate 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 even 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 to remove laitance. Do not acid wash before acid staining!
For old concrete, a thorough cleaning is necessary. In general, 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 do a small test area first.
Since the stain contains acid, it is dangerous to work with. Extreme caution should be used when working with acid stain. Wear eye protection, rubber gloves, have plenty of ventilation and follow the manufacturer's directions to the letter.
Acid stain application involves very 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 uniformly 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 enable you to create more eye-catching designs.
Use a 4-inch and 7-inch saw with diamond blades. Mark your lines with chalk, and cut to a depth of about 1/4 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 over 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 business 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. The acid-stain market is a long way from being well-known and developed, but it has a very bright and shiny future.
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