Acid Etch Concrete

Concrete that hasn't been treated in any way after being poured can be too hard and smooth to accept paint or protective sealants. However, etching (or washing) concrete with acid opens the pores of the concrete and prepares the surface to accept its next treatment. Though it's also possible to prepare the concrete manually by abrading it with a grinder, acid etching is generally much less labor-intensive.

Steps

Preparing to Etch

1. Grab muriatic acid or another suitable etching acid. Before you start your etching, you'll want to make sure you have enough of a suitable acid to complete your project — having to run out to the hardware store in the middle of your etching project is a serious pain. Muriatic acid (also called hydrochloric acid) is the most common type of acid used for this project. It's difficult to say exactly how much acid any given project will need because the acid is usually sold in varying strengths. In very general terms, {{safesubst:#invoke:convert|convert}} of acid (when properly diluted) will cover about 50-70 square feet of concrete (about 4.5-6.5 square meters).
   • Other suitable acids for etching include phosphoric acid and sulfamic acid. The latter is an especially good choice for first-timers because it is much less caustic and dangerous than the other acids.
   • If you're unsure of whether you have the right type of acid, check the label on its packaging — most suitable products will mention that they can be used for concrete etching purposes.
2. Clear the concrete of any obstructions. To begin, remove any any all furniture, vehicles, and other obstructions from the area you intend to treat. Etching acids can permanently damage common objects if allowed to remain in contact with them for even short periods of time, so have them well out of the way by the time you start your project.
   • You'll also want to give the area a good sweeping to remove accumulated dust, dirt, or grime. The acid needs to be able to touch every part of the concrete's surface to react properly with it. Even small pieces of debris can interfere with the reaction, potentially causing an uneven etching.
3. Use degreaser for oil or grease. If you're etching concrete in your garage or on your driveway, there's a chance that there may be oil or grease stains on the driveway from your vehicle. Etching acids can't penetrate through oily substances, which means that any concrete under an oil stain will go un-etched. To remove oil and grease stains, try scrubbing with a commercial degreasing product — these are available from most home improvement stores for fairly cheap.
   • Alternatively, try using ordinary laundry detergent. Most detergents are formulated to dissolve oil and grease, making them perfect for degreasing your concrete surface.
4. Hose down the entire area. When your concrete is perfectly clean and clear, use a hose with a sprayer attachment to wet the entire surface of the concrete. Spread the water evenly across the surface until all of the concrete is wet but no standing water remains. The concrete should stay at this level of wetness until the acid is applied.
   • If you'll be etching up to any adjacent walls or other surfaces, be sure to also wet the bottom inch or so to minimize the possibility of direct contact with the acid.

Applying the Acid

1. Mix water and acid in 3 or 4:1 ratio. Add clean, clear water to a plastic bucket. Very carefully pour your acid in, being sure not to cause any spills or splashes. Don't use a metal container — acid can corrode many metals, leading to the possible destruction of the container.
   • Always pour acid into water. Never pour water into acid. If acid splashes back into your face, it can lead to disfiguring injuries or even blindness.
   • From this point forward, you'll want to observe basic acid safety measures. Wear long sleeves, gloves, eye protection, and, if necessary, a face mask to protect against any fumes. For more information, see the safety section below.
2. Test the mixture in a small space. Most 3:1 or 4:1 mixtures of acid will be a suitable strength for etching concrete. However, before you pour your mixture on to the floor, it's a very wise idea to test it on a small, unimportant area of the concrete (like a spot that would normally be covered by furniture or tool boxes) to make sure it works. Pour about 1/2 cup directly on to the concrete. If it's strong enough, it should immediately begin to bubble and react.
   • If you don't immediately see bubbles, your mixture probably isn't strong enough. Consider carefully adding more acid.
3. Use a sprayer or watering can to distribute the acid. Rather than pour all of the acid onto one spot of the floor, which can leave some of the acid spent by the time it reaches the far corners of the concrete, use a plastic sprayer or watering can. This ensures a more even application. Immediately after spraying, use a squeegee to manually distribute so that the whole floor receives an even coating. You may also use a floor machine to scrub the floor and distribute the acid.
   • The floor needs to stay wet the entire time you are acid etching. Don't let the acid dry on the floor — if you need to, hose down areas that are drying out.
4. Wait for the acid to react with the floor. When you're sure that your acid has been evenly applied, simply step away from the floor and wait for it to stop bubbling. Usually, this will take about 2-15 minutes. As the acid reacts with the floor, it will open up small, porous holes in the concrete, making it much more accepting of your intended sealant.
   • Inspect the surface as the acid works. You want the acid to be reacting evenly and uniformly across the surface. If there are spots where the acid isn't reacting, this can be a sign that an unnoticed grease stain or sealant was present on the concrete. In this case, you may need to use a mechanical solution, like a grinder, to finish etching the concrete.
5. Neutralize the surface. Check your acid's label — many will require using a special neutralizing solution to stop the reaction of the acid, while some others may "time out" on their own. For acids that require a neutralizing solution, mix the neutralizer and distribute it throughout the floor according to the instructions on the packaging. Usually, you'll need to spray the neutralizer and scrub with a squeegee or use the floor machine to ensure the entire surface has been neutralized.
   • For a general, all-purpose acid neutralizer, try mixing 1 cup of baking soda in {{safesubst:#invoke:convert|convert}} of water, then mixing until it dissolves.
6. Rinse the floor thoroughly. At this point, your concrete should have a clean, freshly-etched appearance. You're now ready to clean up. Use a broom or squeegee to gather the rinse water into one area, then suck it up with a shop vacuum. Read packaging instructions for how to properly dispose of your acid — you may have to add more baking soda to further neutralize it before pouring it down the drain.
   • Alternatively, if you're working in a garage, you may be able to simply rinse your neutralized solution directly out of the garage and into a drain. Check your local regulations before doing this — you don't want to break the law or hurt the environment.

Treating Concrete After Etching

1. Apply sealant or epoxy. Many acid etching projects are carried out to prepare a concrete floor for the application of a synthetic epoxy or sealant. These sorts of products give the concrete a professional-looking sheen and also resist water, grease, oil, and other common spills, making the floor easy to maintain. In addition, using an anti-skid additive in your sealant can give your garage or driveway surface the traction your vehicle needs to securely grip it in rain or snow.
2. Use a pigment or stain. Adding a stain or pigment to the concrete after etching is a great way to make it more visually attractive. For some interior spaces, stained concrete can give a clean, elegant, modern look to the room. Even some outdoor spaces, like patios, can use stained concrete to great effect.
3. Paint the concrete. Concrete can also be painted fairly easily with brushes, rollers, or sprayers. Though it's a little less common to paint a concrete floor than it is to paint a concrete wall or ceiling, some decorators can create breathtaking interior spaces with the help of painted concrete floors. For painted concrete floors, generally, low-sheen, matte paints are used — otherwise, the floor can appear oddly shiny or "wet".
4. Add metal flakes for a sparkly surface. Many sidewalks, driveways, and other exterior concrete surfaces can be given an appealing sparkling quality by adding metal chips flakes before sealing or during the etching process. Even some interior spaces (especially public or commercial ones) can benefit from this type of treatment — for instance, sparkling concrete floors are sometimes used in shopping malls and airport corridors to give a lively look.

Handling Acid Safely

1. Wear protective clothing. All acids (but especially the strong ones used for concrete etching) should be handled with care. If splashed onto the body, caustic acid can cause painful chemical burns. Worse still, acid can cause permanent blindness and disfigurement if splashed into the face and eyes. Because of this, it's important to always wear protective gear when working with acid, even if you're very experienced. Below are the sorts of protective clothing you should wear to protect yourself:
   • Chemical safety glasses or goggles with face shield
   • Gloves
   • Long sleeves
   • Close-toed shoes
2. Don't breathe the fumes of the acid. Strong acids like muriatic acid can give off harmful vapors. If breathed, these fumes can cause chemical burns in the mouth and throat. Though rare, it's technically possible to seriously hurt or even kill yourself by breathing acid vapors. For these reasons, you'll want to ensure that your work area is well-ventilated at all times. For instance, you'll probably want to open any adjacent windows and use a fan to keep air continually circulating into and out of your work area.
   • If the acid's fumes are strong, use a breathing mask with acid vapor cartridges to prevent injury.
3. Always pour acid into water, not the reverse. This is a hugely important basic rule of acid safety. Whenever you pour and mix acid and water, you always pour the acid into the water. You never pour the water into the acid. If you pour either liquid too quickly, you can cause the liquid in the container to splash back into you. If this liquid is mostly water, you'll probably be fine. However, if it's mostly acid, you can be in serious trouble. Always observe this simple rule when working with acid.
   • It may be helpful to keep a second bucket or plastic container with you while you work. If you accidentally pour acid into the first container first, you can pour water into the second container and then transfer the acid to it to easily correct for your error.

Tips

• Please note muriatic acid is dangerous and must be diluted before use. Read all label instructions before application and wear the proper safety gear when applying.

Warnings

• Again, muriatic acid can be dangerous - be sure to take the proper precautions.

Related Articles

• Acid Stain Concrete
• Acid Wash Concrete
• Prepare Concrete Before Staining It

Sources and Citations

• http://www.ghostshield.com/acid-etching/ - Original Source, Shared with Permission

See also

• Remove Rust from Cement
• Drill Into Concrete
• Tie Rebar
• Build a Concrete Sidewalk
• Break Up Concrete
• Pour a Concrete Patio
• Pour a Concrete Foundation
• Paint a Concrete Floor
• Figure Concrete Yardage
• Acid Stain Concrete

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• Acid Stain Concrete
• Acid Wash Concrete