The Art of Acid Stained Concrete

Learn how to use acid-based chemical stains to impart rich, earth-toned color to plain concrete floors
Updated May 12, 2020

Reformed Concrete LLC
Quarryville, PA

Staining imparts a luxurious richness that can't be achieved by any other coloring medium. Rather than produce a solid, opaque effect like paint, stains permeate the concrete to infuse it with luminous, translucent tones that vary depending on the surface they are applied to and the application techniques used. The results can mimic everything from polished marble to tanned leather to natural stone or even stained wood.

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Stained Concrete Information

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Acid Stains Vs Water-Based Stains

Stains for concrete come in two general categories: acid-based chemical stains and water-based acrylics. Both types of stain can be applied to new or old and plain or integrally colored concrete. They are especially effective for revitalizing dull, lackluster surfaces. Because they penetrate the concrete surface, most stains have excellent UV stability and wear resistance, permitting their use on interior or exterior concrete.

Applications range from:

  • Walkways and patios
  • Family room floors
  • Kitchen countertops
  • Vertical surfaces like walls or fireplaces

Stained Concrete Floors-Ideas for Concrete Stains
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Most acid stains are a mixture of water, hydrochloric acid and acid-soluble metallic salts. They work by penetrating the surface and reacting chemically with the hydrated lime (calcium hydroxide) in the concrete. The acid in the stain lightly etches the surface, allowing the metallic salts to penetrate more easily. Once the stain reacts, it becomes a permanent part of the concrete and won't fade, chip off or peel away. The palette for acid-etch staining is generally limited to earthy tones, such as tans, browns, terra cottas and soft blue-greens.

If you want to go beyond the subtle drama and subdued earth-toned palette of acid staining, consider using water-based stains, which come in a much broader spectrum of hues. Most manufacturers offer dozens of standard colors, including black and white and even metallic tints. Like acid stains, water-based stains (typically a blend of acrylic polymers and pigments) penetrate the concrete to produce permanent color, ranging from translucent to opaque depending on the product.

Like stains for wood, concrete stains are semi-transparent and are intended to enhance rather than disguise the surface. They will not hide cracks, blemishes or other flaws in existing concrete. Nor will they completely mask an underlying color or conceal the texture of the surface. An existing concrete slab with major cracks or spalling is usually not a good candidate for staining because any patchwork is likely to show right through the stain.

Because stains must be able to soak into the concrete to achieve full color saturation, they shouldn't be applied to surfaces covered by anything that can inhibit stain penetration, such as dirt, grease, glues, coatings, curing membranes and sealers.

Indoor vs Outdoor Stained Concrete

Most concrete stains on the market today, whether they are water-based or chemically reactive (acid-based), can be used on both interior and exterior concrete. So how do you determine the best product to use for a particular project? The factors that come into play aren’t much different than those you would consider for indoor vs. outdoor painting: exposure conditions, the look you’re trying to achieve, ease of application, and safety and environmental concerns.

Check out these popular staining applications:

A bowling alley floor colored with water-based stains. Impressions Decorative Concrete, Inc in Lutz, FL

Indoor staining

Is the stain safe for indoor use?
Read the safety precautions provided by the stain manufacturer. For indoor projects where ventilation is poor, concrete stains with a low VOC content will be your best choice. Some chemical stains contain solvents and corrosive components that can cause eye, skin, and lung irritation.

What are the cleanup requirements?
Chemical stains can be messy to use indoors because you must scrub the slab thoroughly after applying to remove any stain residue, followed by rinsing with clean water. Then you must collect all the residue with a wet vac and dispose of it safely (see Acid Staining Basics). Water-based stains are easier and safer to apply indoors because they are free of solvents and acids, and they don't require neutralization or rinsing.

What look are you trying to achieve?
If you want to match an existing color scheme or make a bold design statement, water-based stains will give you an endless array of color options and, like wall paint, can be mixed to create custom shades. (See how water-based stains were used to add vibrant color to this bowling alley floor.) If you want to achieve rich earth tones with natural marble-like color variations, chemical stains are often the best choice, as long as the proper precautions are taken during indoor application. On this residential floor project, chemical stains in dark walnut and antique amber were used to create an appealing vine pattern.

Is your floor slab emitting moisture?
For the best results, concrete stains should be applied to interior slabs that have a low moisture-vapor emission rate. Some manufacturers recommend performing a moisture-vapor emission test to check for suitability.

Will acid stain kill vegetation and grass when used outdoors?
For outdoor projects, the fumes from acid stains will not pose much of a problem. However, the residue and runoff from rinsing off the stain must be contained because it could harm the grass and surrounding vegetation. Water-based stains don’t require rinsing and any residue can be safely cleaned with soap and water.

Does the color work with your landscape and home exterior?
If you want to replicate the appearance of natural aged stone, chemical stains will react chemically with the mineral content of the concrete to create a beautiful mottled appearance (see this acid-stained patio). Water-based stains are non-reactive, so the color tends to be more opaque and uniform. However, water-based stains will give you more color options and the ability to customize colors to coordinate with the color scheme of your home exterior. For this residential driveway project, solid-color water-based stains were used to match the home’s existing design scheme.

Use a good sealer

Whether you’re staining indoor or outdoor concrete, all stained surfaces should be protected with an appropriate sealer, which is determined by the type of stain, exposure conditions, and the level of traffic. Not only does the sealer provide protection from day-to-day wear, it also enhances the color and determines the gloss level of the finish. For indoor projects, lower gloss levels tend to be easier to clean and won’t show wear or surface scratching as much as high-gloss sealers. Learn more about choosing the best sealer for your project.

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