Are you looking for ways to breathe fresh life into a dull patio surface? Consider acid stains, one of the oldest methods to change concrete’s color. This technique can layer and blend subtle translucent shades into eye-catching, marbled effects across large or small slabs.

However, before you update your patio with an acid-based stain or add stain to a new patio, it’s essential to get familiar with several of the most common questions homeowners ask: 

1. How do acid stains work?

Acid-based stains rely on a chemical reaction to change concrete’s color from within. It’s a different process than applying paint to a patio’s surface. 

With an acid stain, you typically mix water, hydrochloric acid, and various blends of metallic salts. The acid lightly etches the surface, allowing the salts to soak in and start reacting with the lime in the concrete. 

Over several hours, the color will slowly change as the chemical reaction progresses—or until a neutralizer is applied. Overlapping shades of stain may be used (before neutralizing) to produce an effect with additional color depth.

2. Is acid staining permanent?

Yes, acid stains are permanent. You can achieve a darker shade by letting the chemicals work longer, but you’ll never be able to lighten it. 

3. What colors are offered?

Acid stains rely on chemistry to create colors, and the results are more limited than pigment-based paints and dyes. 

Most acid-stain color charts include a wide range of browns, including light tans, rusts, deep sable, and soft blue and green hues. However, green and blue shades can’t be used outside because they contain copper and will turn black with repeated exposure to moisture.

4. Is acid staining effective on all concrete surfaces?

Yes and no. Significant differences can exist in how acid stains react with concrete, depending on factors like a patio’s age and finished surface. 

For example, acid stains won’t penetrate a tightly troweled surface easily because it acts like a sealer. Additionally, older concrete slabs won’t react to acid staining as readily as newer concrete. And a fresh concrete slab needs to fully cure before applying an acid stain.

Ideally, you’ll want to test your stain in an inconspicuous spot before you commit to using it on the entire patio surface.

5. What happens after the staining process?

After the color is fully developed, it’s essential to thoroughly clean, neutralize, and rinse the surface. 

A neutralizer eliminates the possibility of ground moisture wicking up and triggering another color reaction. And a cleaner will eliminate any salts that have risen to the surface, leaving a powdery residue.

Finally, a penetrating sealer will protect the concrete from undesirable stains.

6. What about water-based concrete stains?

You can also stain a concrete patio with a water-based stain, but the products and processes differ significantly from acid stains. Water-based stains are pigmented coatings applied to the surface instead of relying on a chemical reaction within the concrete.

You must ensure the surface is rough enough for a water-based stain to bond well. Refer to the manufacturer’s application directions for specific recommendations and follow them closely.

One advantage of water-based stains is that you can select from a much larger color palette. However, this type of stain is more vulnerable to sun fading and must be resealed periodically.