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Acid Stained Concrete Flooring
by Dr. Oneida Cramer

"Concrete is a misunderstood material," says Earl Snow, owner of Tolman-Snow Concrete Staining. "The integrity of it is so beautiful. But people haven't really understood the beauty of it and how much use there is in concrete if you finish it right."

Frank Lloyd Wright (1869-1959) was a proponent of timeless materials, and from 1903, he used concrete in most of his structures' slabs, walls, ceilings, and columns for structure and decoration.

"Architects have always loved the product," said Barbara Sargent, distributor of Kemiko Concrete Floor Stain. "And the main reason is that it really doesn't compete with their design. It just blends in a way of simplicity. Also, architects have understood the concept of stained concrete for a long-long time."

"It's like using a canvas backdrop when you're taking a photograph," said Snow. "Anytime you use a mottled multi-layered textured looking backdrop, the things that are in front of it are projected even better. That's what it (concrete) does to your furniture and your rug and everything else." When Snow started staining concrete 28 years ago, his clients were designers and architects, primarily. Today, Snow finds many homeowners coming directly to him.

About 12-14 years ago, trying to figure out why we were having such serious allergy problems began the mass movement of people tearing up their old carpet and not replacing it with new carpet, according to Sargent. Homeowners found themselves living on hard sub-floor surfaces, which in peer and beam homes meant hardwood floors. In slab foundation homes, concrete flooring began appearing underfoot.

"People weren't afraid to stain the concrete in their homes because it really doesn't rule out any options," Sargent said. "If you were to stain your floor and then, say in 10 to 12 years, sell your home, the next buyers come in and either understand and appreciate the concept or they don't. It's still just the slab that the house started with. And you've not ruled out any options."

"The other thing is cost," said Sargent. "Not only is concrete stain economical to apply (one gallon of stain at $47.95 will do a 2-car garage). It's easy to do by yourself. And the best part about it is that it's permanent.

"Being that concrete is really a natural type of product, we don't paint it to cover up the concrete, we stain it with a chemical acid stain that has iron oxide and metallic salts that chemically react with the concrete," Snow said. On old, new, plain and decorated concrete, the acid opens up the surface and allows metallic salts to reach the lime deposits. Color is the insoluble compound that appears as a result of reactions between metallic salts and the calcium in the lime. These reactions can continue for about a month after applying the stain, and weather conditions can influence the extent of the reaction, according to the concrete network ( For instance, on sunny days, stains may not penetrate very far under surface if the concrete is hot and dry. In wet weather, color may penetrate deeper and be richer than expected. Also, reactions vary due to age and moisture content of the concrete and its composition.

In general, cements that produce larger amount of calcium hydroxide will show more color stain, and concrete with a higher content of cement will produce more intense color. This phenomenon is due to the manufacture of concrete: concrete is made up of cement, water, sand (fine aggregates), granite (course aggregates), and ash. The glue that holds the concrete together is cement, a mix of fine powders from limestone, chalk, clay, and slag (chemical composition-silica, lime, alumina, iron oxide, and magnesia). When cement is added to water along with aggregates, it hardens like stone into concrete. It is in this hard state that lime (calcium oxide) first reacts with water in the acid stain to form calcium hydroxide, which, in turn, reacts with metal oxides to form the color.

"The lime pockets are distributed randomly throughout that entire slab," Sargent said. "And you don't have a clue where the lime is. So, you come up with a varied, mottled/marbleized, stone appearance." And color usually imbeds down to about 1/16th of an inch into the concrete.

Homeowners can always re-stain darker, according to Sargent "from malay tan, a buckskin tone with caramel marbling; to green, a soft gray green resembling old marble; to cola, a reddish brown old leather look; and to black with lots of brown tortoise shell color. But coloring can't reverse towards the lighter shades.

A search of the Internet came up with one possible reversing agent, Launch Concrete Restoration System, which uses a chemical approach to restore stained concrete to 'like-new' appearance. This compound, available in 5-gallon commercial pails or in pre-packaged residential kits, does reverse the types of chemical reactions that occur in concrete floor staining, according to Scott Fay, ( However, Fay is not aware of this system having been used in decorative staining. Indeed, wanting to reverse decorative concrete staining has never been requested, says Snow, because the look is so timeless.

"We're not trying to look like tile," Snow said. "We're trying to look like stone." And a way to accentuate the stone character is to score the concrete' cut a pattern' any kind of a pattern using a diamond saw. In fact, Snow has been called an artisan because of his patterns. Costs depend on the design; yet average cuttings, for instance, two to three-square-foot, diagonal patterns with staining, waxing or sealing costs between $2.50 to $3.50 per square foot.

"You save money. But you don't compromise the quality of your home," Snow said. "In fact, you enhance the quality." Favorite areas for staining have been the entry and hall, the utility room, kitchen, and family room floors. And many homeowners, even homebuilders, are doing their entire homes, for instance, a Tuscany style. Time wise, a 2,000 square-foot house takes about two to three days.

"It's a very old look to it," Snow said. "We burnish it-wax your concrete." Waxing imparts a soft subtle glow. For a look that's sleek, high-gloss and wet looking, concrete sealers are applied over the stain. About 92% of people prefer the wax, according to Sargent, because wax allows marbling to show through where the sealer darkens and subdues color variation.

Stained concrete is also gaining popularity as kitchen countertop material. And outdoors, where sealers and waxes are not applied, stained concrete is used decoratively on patio floors, paving around pools, and porches.

"It's fun to do a patio," Sargent said. "And then way out in the distance in your garden, do a bird bath or settee in concrete in the same color to drag your eye out."

-by Dr. Oneida Cramer
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