How to acid etch concrete

How to acid etch concrete

Muriatic acid is the type of acid that is typically used for etching concrete. It can be highly toxic so we recommend using the Hydro-Etch 1000, a specialized muriatic acid and phosphoric acid blend which has less fumes than regular muriatic acid and is used to clean concrete, brighten concrete and etch concrete.

For an even safer concrete etching product use the Eco-Etch 1001: a safe, powerful, 100% biodegradable concrete cleaner with no acid, solvents or VOC’s specifically formulated to clean, brighten and etch concrete without any harmful effects. Although it ususally does not create as much surface profile as using straight muriatic acid, it does an excellent job at giving concrete light surface profile.

Before etching you want to make sure everything is removed from the surface you are including cars and furniture. Sweep up the area to remove as much dust and dirt as possible.

Follow basic safety precautions by wearing long sleeves, gloves, eye protection and a respirator face mask to protect from fumes.

Acid is generally mixed at a ratio of 3 parts water to 1 part acid for sufficient strength to etch properly. Ideally you want to test the strength needed first before doing the entire floor. You can do this by first mixing a small solution in your watering can starting at a 5:1 ratio. Apply it to a small area of wet concrete. It should begin bubbling and fizzing immediately. If not then you will want to increase the strength accordingly. Sometimes a ratio stronger than 3:1 may be needed for particularly dense concrete or a smooth power troweled floor.

Caution! Always add acid to water, not water to acid. If you pour water into acid it can cause an explosive reaction that can spray you with the mixture and burn your skin!

Before acid etching, make sure the concrete is free of all oil, contaminants, grease, and dirt. Contrary to what many people think, acid will not clean grease and oil spots. In fact, if these areas have not been cleaned and degreased properly, the acid solution will just sit on top and not react with the concrete.

Dampen the concrete: Use your hose to lightly spray down the concrete in your garage so that the concrete is wet but not puddling water. If you have a large floor, you may want to acid etch in sections. Do not let the concrete dry out before or during application of the acid solution.

Apply the acid solution: Use the 2 gallon plastic watering container to sprinkle the acid solution on the concrete. This will spread the solution evenly without much splashing. Do not just pour it on the concrete. This will create an inconsistent spread of the acid solution and will not provide for a uniform result. The 2 gallon container works well because you can mix 1.5 gallons of water to .5 gallons of acid for a 3:1 ratio. You can use any size you like however, as long as you mix the ratio of acid to water correctly. 1 gallon of acid solution will cover approximately 50 – 70 square feet of garage floor.

Scrub the acid solution: Once the solution is applied, lightly scrub it into the concrete with a push broom or long handled scrub brush. This helps to create a uniform etch of the concrete. Let the solution sit from 2 – 15 minutes while it continues to fizz and bubble. Do not let the floor dry out during this process. Add more solution if necessary.

Neutralize: Mix 4 cups of baking soda to 1 gallon of water in your large 5 gallon bucket and pour it into the now empty watering container. Or use 4 ounces of household ammonia to 1 gallon of water. Sprinkle your neutralizing solution over the part of the floor that was acid etched and let it sit for a minimum of 10 minutes. When time is up, rinse the neutralized solution with your hose into a drain or out the garage (if local water codes allow it). Another method is to use a wet vac and then dispose of the solution according to your local codes. Check the surface of the concrete at this time. It should feel similar to medium grit sand paper with a uniform texture. If not, you will need to repeat the process again.

Final rinse: Once the initial neutralizing solution is cleaned up, it is important to thoroughly flush and rinse the remaining solution out of the concrete multiple times. It can leave a white powdery residue on your floor once dried (called calcium carbonate) if you do not do this. This is a fine dust that will not allow your coating to adhere properly. Use a high pressure nozzle while thoroughly scrubbing the concrete with your scrub brush. You can introduce a mild solution of Simple Green at this point if you like. Just make sure it is thoroughly rinsed. Using a pressure washer at this point works well also. Do not use a pressure washer to rinse off the initial neutralizing solution however. It can drive any acid solution that had not been neutralized yet deeper into the concrete and cause problems later.

  • pH test your rinse water: After your final rinse, dab a pH test strip onto the still wet floor to check the pH. Anything between 6.0 and 9.0 will work for most coatings with 7.0 (neutral) being ideal. If it’s below 6.0 then the water is indicating that acid residue is still in the pores of the concrete. Rinse some more and repeat the test until you get the results you want.
  • Further tips for Acid Etching:

    It’s a good idea to cover anything that you don’t want to get splashed with a plastic drop cloth. Don’t acid etch the concrete if the temps are below 50 degrees F as the acid will not be as effective with the cooler temperatures.

  • Also, make sure your floor has dried thoroughly before applying a concrete sealer. Fans will help. Give it at least two days with warm weather and longer if it’s humid or cooler. Though the surface may be dry, the pores of the concrete can still contain moisture and escape through outgassing when the temperatures rise during the day. This will cause your coating to not properly adhere. You can always do a quick moisture test with plastic if you are not sure.
  • How to acid etch concrete

    Hydro-Etch 1000

    Acid etch & concrete cleaner

    Published Friday 12th of September 2014 // Updated Monday 29th of March 2021

    How to acid etch concrete

    Muriatic acid is the type of acid that is typically used for etching concrete. It can be highly toxic so we recommend using the Hydro-Etch 1000, a specialized muriatic acid and phosphoric acid blend which has less fumes than regular muriatic acid and is used to clean concrete, brighten concrete and etch concrete.

    For an even safer concrete etching product use the Eco-Etch 1001: a safe, powerful, 100% biodegradable concrete cleaner with no acid, solvents or VOC’s specifically formulated to clean, brighten and etch concrete without any harmful effects. Although it ususally does not create as much surface profile as using straight muriatic acid, it does an excellent job at giving concrete light surface profile.

    Before etching you want to make sure everything is removed from the surface you are including cars and furniture. Sweep up the area to remove as much dust and dirt as possible.

    Follow basic safety precautions by wearing long sleeves, gloves, eye protection and a respirator face mask to protect from fumes.

    Acid is generally mixed at a ratio of 3 parts water to 1 part acid for sufficient strength to etch properly. Ideally you want to test the strength needed first before doing the entire floor. You can do this by first mixing a small solution in your watering can starting at a 5:1 ratio. Apply it to a small area of wet concrete. It should begin bubbling and fizzing immediately. If not then you will want to increase the strength accordingly. Sometimes a ratio stronger than 3:1 may be needed for particularly dense concrete or a smooth power troweled floor.

    Caution! Always add acid to water, not water to acid. If you pour water into acid it can cause an explosive reaction that can spray you with the mixture and burn your skin!

    Before acid etching, make sure the concrete is free of all oil, contaminants, grease, and dirt. Contrary to what many people think, acid will not clean grease and oil spots. In fact, if these areas have not been cleaned and degreased properly, the acid solution will just sit on top and not react with the concrete.

    Dampen the concrete: Use your hose to lightly spray down the concrete in your garage so that the concrete is wet but not puddling water. If you have a large floor, you may want to acid etch in sections. Do not let the concrete dry out before or during application of the acid solution.

    Apply the acid solution: Use the 2 gallon plastic watering container to sprinkle the acid solution on the concrete. This will spread the solution evenly without much splashing. Do not just pour it on the concrete. This will create an inconsistent spread of the acid solution and will not provide for a uniform result. The 2 gallon container works well because you can mix 1.5 gallons of water to .5 gallons of acid for a 3:1 ratio. You can use any size you like however, as long as you mix the ratio of acid to water correctly. 1 gallon of acid solution will cover approximately 50 – 70 square feet of garage floor.

    Scrub the acid solution: Once the solution is applied, lightly scrub it into the concrete with a push broom or long handled scrub brush. This helps to create a uniform etch of the concrete. Let the solution sit from 2 – 15 minutes while it continues to fizz and bubble. Do not let the floor dry out during this process. Add more solution if necessary.

    Neutralize: Mix 4 cups of baking soda to 1 gallon of water in your large 5 gallon bucket and pour it into the now empty watering container. Or use 4 ounces of household ammonia to 1 gallon of water. Sprinkle your neutralizing solution over the part of the floor that was acid etched and let it sit for a minimum of 10 minutes. When time is up, rinse the neutralized solution with your hose into a drain or out the garage (if local water codes allow it). Another method is to use a wet vac and then dispose of the solution according to your local codes. Check the surface of the concrete at this time. It should feel similar to medium grit sand paper with a uniform texture. If not, you will need to repeat the process again.

    Final rinse: Once the initial neutralizing solution is cleaned up, it is important to thoroughly flush and rinse the remaining solution out of the concrete multiple times. It can leave a white powdery residue on your floor once dried (called calcium carbonate) if you do not do this. This is a fine dust that will not allow your coating to adhere properly. Use a high pressure nozzle while thoroughly scrubbing the concrete with your scrub brush. You can introduce a mild solution of Simple Green at this point if you like. Just make sure it is thoroughly rinsed. Using a pressure washer at this point works well also. Do not use a pressure washer to rinse off the initial neutralizing solution however. It can drive any acid solution that had not been neutralized yet deeper into the concrete and cause problems later.

  • pH test your rinse water: After your final rinse, dab a pH test strip onto the still wet floor to check the pH. Anything between 6.0 and 9.0 will work for most coatings with 7.0 (neutral) being ideal. If it’s below 6.0 then the water is indicating that acid residue is still in the pores of the concrete. Rinse some more and repeat the test until you get the results you want.
  • Further tips for Acid Etching:

    It’s a good idea to cover anything that you don’t want to get splashed with a plastic drop cloth. Don’t acid etch the concrete if the temps are below 50 degrees F as the acid will not be as effective with the cooler temperatures.

  • Also, make sure your floor has dried thoroughly before applying a concrete sealer. Fans will help. Give it at least two days with warm weather and longer if it’s humid or cooler. Though the surface may be dry, the pores of the concrete can still contain moisture and escape through outgassing when the temperatures rise during the day. This will cause your coating to not properly adhere. You can always do a quick moisture test with plastic if you are not sure.
  • How to acid etch concrete

    Hydro-Etch 1000

    Acid etch & concrete cleaner

    Published Friday 12th of September 2014 // Updated Monday 29th of March 2021

    How to acid etch concrete

    Chemical Cleaning

    If you are an industrial user with a large area, then you may be better to consider mechanical preparation. However, for smaller areas / domestic users, an alternative method is with the use of an acid based solution – Polycote Etch IT

    Acid Etching

    Etch IT is a very low cost chemical method commonly used to treat concrete floors to remove laitance and provide a profile. The objective of acid etching is to dissolve the weak surface layer known as laitance and open the pores to allow penetration of the sealer coat.

    1. Should you wish to remove greases, oils, or other types of contaminants, these can be treated with Polycote Degrease IT prior to the etching procedure.
    2. Acid Etching will not be effective over release agents and/or most surface hardeners.
    3. In sensitive situations, the use of phosphoric acid (which is non-volatile) could be considered as an alternative to Etch IT – which is a hydrochloric acid.
    4. Etch IT will be of no use whatsoever to a painted surface. It is only for use on bare concrete concrete and metal. How to acid etch concrete

    Pre-Dampen The Surface

    Pre-dampen the surface with clean cold water taking care to remove any puddling areas or excess surface water. This dampening is only to remove the immediate suction of a dry surface as we do not want the acid soaking down into the substrate. The ‘treatment’ is only for the loose/friable material on the surface.

    Diluting The Acid

    Polycote Etch IT is a concentrated Hydrochloric Acid and should be diluted with water. The dilution ratio is normally 3 parts water to 1 part acid but can be both stronger or weaker, depending upon the quality / porosity of the concrete being treated.

    1. When mixing the water and acid together, it is important to add the acid to the water – NOT he water to the acid.
    2. Should there only be a weak reaction of the acid solution, or an absence of bubbles altogether, this can be an indication of:
    3. The presence of a surface hardener – which will prevent the reaction of the acid
    4. The solution being too weak / concrete too hard. Increase the quantity of acid solution to the water until there IS a reaction on the surface.

    Application

    Using a relatively stiff broom, the diluted acid should then be applied uniformly over the surface. The acid will bubble and/or ‘fizz’ for the following 3-5 minutes during which you can scrub the surface with the broom to help facilitate the etching process. The bubbling/fizzing reaction of the solution indicates that the etching is indeed strong enough and is completing its work.

    Once etching is completed – and BEFORE the surface has dried, wash the area thoroughly with fresh cold water to help remove the surface dust / loose material and also to neutralize the surface.

    Brush the water out of the door and depending upon local regulations, this can now be washed down the normal drainage system. By the time it has been sent down the drain, it should have been well neutralized by the amount of water used to wash the floor. However, should you wish to be absolutely sure then simply send a goodly quantity of fresh clean water down the drain with the use of a hose pipe.

    Please note that if the surface DOES dry before this washing process, it can allow the formation of salts on the surface and once formed, these salts are difficult to remove!

    Scrubber / Drier

    Alternatively, the use of a mechanical scrubber / drier is good for removing the water and debris, although take care to thoroughly wash out after use to ensure there be no degradation to the rubber seals, etc.

    Result:

    Properly etched concrete will leave the surface hard and slightly textured. More importantly, the pores will now be opened and thereby allow the subsequent treatment/coating to penetrate well into the surface.

    Important:

    1. Both hydrochloric and phosphoric acids are commonly used in the preparation of floors. However, please do use with care as they can cause burns to skin and the inhalation of acid fumes can also cause discomfort. Using the correct personal protection, your job can be completed quickly, easily and safely
    2. As the pores of the concrete are now open, please make sure the area is not used / contaminated prior to sealing the floor with your chosen coating.

    FURTHER TECHNICAL HELP REQUIRED?

    Thank you for your interest and we hope you have found the above information both interesting and helpful. However, should you still have be unsure as to the best solution for your needs, please don’t hesitate to ring our technical helpline now on 01234 846400. We have a fully qualified team ready to give practical advice and help assist you as much as possible.

    Some homeowners shy away from acid etching of their concrete floors for fear of the harmful effects of using and handling muriatic acid, the main component of acid etch flooring. The good thing is that there are safer alternatives that are just as effective available in the market today.

    Muriatic acid or hydrochloric acid has long been the accepted acid etching method of professional installers and homeowners. However, this chemical is not ideal for household use because of its damaging and harmful effects. Muriatic acid easily melts anything it comes in contact with, like most types of plastics, clothes, metal, and even your skin. Furthermore, its fumes are known to burn the lining of the nose and lungs.

    Because of these harmful effects, manufacturers have started developing products that are environment-friendly and safe to use. Also, these new alternatives have no VOCs and do not emit harmful fumes.

    What is Garage Floor Acid Etching?

    Before giving you the alternatives, it is important to give you an idea of what acid etching is. Acid etching is done to prep a concrete floor before applying the coating. It is not hard to do, but there are safety measures to consider in its handling and application since hydrochloric acid has potentially harmful effects on the installer’s health and on the environment. Proper handling is imperative because the acid is in liquid form. It can also damage concrete if etching is not done properly.

    Aside from the more popular hydrochloric acid, phosphoric acid can also be used. It is a mineral acid which is just as effective but without the harmful effects. However, it is harder to find and it costs more than hydrochloric acid. Phosphoric acid can emulsify oils, something that hydrochloric acid is not capable of doing. Both types of acids can remove rust from concrete flooring.

    Mix 1 part acid to 3 parts water for sufficient strength. Professionals recommend testing the strength needed on one area before applying it on the entire garage floor. Test with a 5:1 ratio in your water can. Apply the mixture to a small area of concrete. You know you have achieved the ideal strength when you see immediate bubbling and fizzling in the area. Failure to get that particular reaction means you have to make adjustments on the ratio. Some concrete floors require 3:1 ratio.

    To avoid explosive reaction when mixing, acid should be added to water and not the other way around.

    Safer Alternatives

    One particular product is Tek Gel for Profiling (TGP), which is gel-based muriatic acid. Hydrochloric acid is placed inside a gel (It looks like a block of gelatin dessert.). The gel is easy to use and it can be directly applied on concrete just by using a nap roller. It’s a one-step application process and you don’t need to mix it with water.

    After the application, lightly scrub the area and let it stand for 10 to 15 minutes. Once the etching process is completed, you can easily hose it off. You can mop off excess water. If you have a wet vac, the better.

    There is also no need to neutralize and it won’t cause damages when flushed down the sewer.

    Tek Gel is becoming popular because with its use, there is little to no oil and grease residue left after you have cleaned the concrete floor. Liquid hydrochloric acid can’t do that. While it costs more than the liquid acid, the gel form provides a more consistent etch on concrete. It is also easier to contain. When you think about the damages liquid acid could make, the cost of $80 per gallon of acid gel is reasonable.

    Another alternative does not use hydrochloric acid in any form. Eco-Etch Pro is a biodegradable product that is plant-based. It is environment-friendly, non-corrosive, can be easily neutralized with water, and doesn’t harm your skin. This product doesn’t emit toxic fumes; in fact, it even has a sweet scent.

    It is a blend of organic minerals, surfactants, and derivatives of a plant extract. Even without hydrochloric acid, it is still an effective etching agent. It is safer and it can be processed faster. It can be used for either interior or exterior surfaces.

    Eco-Etch Pro comes in a concentrate form, meaning it can be used in varying strengths, depending on the type of product you are using for your concrete garage floor. For instance, if you are using epoxy coating, you can use it at full strength. When you are using concrete stain, you can easily dilute it with water following a 3:1 ratio. The manufacturer recommends that you use a floor buffer with black scrub pad to maximize its effects.

    A gallon of concentrate costs around $25, and it can cover approximately 250 square feet of floor.

    Once the floor etching process is done, it is important to check the surface texture and porosity. Take note that the texture and feel of a properly profiled concrete floor is similar to that of medium grit sandpaper.

    Apply a few drops of water on the different areas of the garage floor to test its porosity.The surface should immediately turn black and the water should be completely absorbed into the concrete.

    You need to repeat the etching process if there are areas that did not completely etch.

    Other Benefits of Concrete Etching

    Aside from efficiently etching the concrete garage floor, these two hydrochloric acid alternatives work on dirt, rust stains, and efflorescence. You don’t have to worry about your family’s health because they both don’t produce harmful fumes that may affect the lungs. They are both commercial grade products.

    They are easy to use. In fact, you don’t need to hire a professional installer to work on your garage floor because the instructions are clear and easy to follow. Just make sure that you read and understand the instructions that come with the product and adhere to the precautionary measures listed.

    Allow the concrete garage floor to dry out for a couple of days before the application of your preferred coating. On the other hand, epoxy can be applied even on damp concrete, so you don’t have to wait a few more days if you are using it as a concrete floor coating.

    How to acid etch concrete

    The following is only a suggested guide on acid etching concrete for the application of thin film coatings such as Epoxy and Polyurethanes. Contact Gulf Coast Paint Mfg. for more detailed information on Surface Preparation on concrete surfaces.

    CAUTION: Acid etching requires the use of strong chemicals. Used improperly these chemicals can result in severe injury. When handling harmful chemicals, always wear protective clothing, protective eyewear/face shield, rubber gloves and boots. Do not breathe vapors.

    Always add acid to water. Never add water to acid!

    Protect surfaces not to be etched from chemical vapors, splash and spill.

    Dispose of all residual material according to local and national regulations.

    Scope: Acid Etching of Concrete for the Application of Coating Systems

    Properly clean the concrete surface first before acid etching the floor.

    Properly mix acid solutions.

    Wet-out concrete surface with fresh, clean, un-contaminated water. (No ponding)

    Apply acid solution uniformly.

    Allow acid time to react: 2 – 10 minutes.

    Check profile. Should be between 80 grit – 120 grit open-coat sand paper.

    Check the pH (ideal pH is 7.0, but 7.0-8.5 is acceptable). Neutralize surface if necessary. Rinse/scrub surface.

    Properly clean concrete surface. Remove all dirt, dust, grease, oils, wax, release agents or any other contaminants that will interfere with the acid etching and preparation of the concrete the concrete surface. Mechanical cleaning with stiff bristle brushes by hand or machine will be required for cleaners to work properly. Some contaminants such and sealers and curing compounds may not be removed by cleaning and will require the surface layer of the concrete to be removed by mechanical means. (Shot blasting, sanding, grinding, or any other approved method to remove the contaminant.)

    Before the acid etching process begins Gulf Coast Paint recommends several tests:

    Confirm new concrete is cured 28 days.

    Confirm that a vapor barrier was installed.

    Check for moisture following these 2 test methods that are most commonly accepted in the industry: ASTM 1869 (Calcium Chloride Test) and ASTM 2170 (RH Probe Test) .

    Complete a water dissipation test on random areas of the floor to determine that the proper degree of porosity has been achieved.

    Properly mix acid solution . Acids that can be used to etch the concrete are, muriatic, sulfuric, phosphoric, or citric. The most commonly used are muriatic (hydrochloric-HCL) and phosphoric acids. Use only plastic or acid resistant containers for mixing and applying acid. Acids concentrations can vary. To determine the strength and concentration to use to etch the concrete, test with a very dilute solution then add acid to container until strong bubbling action is noted in the test. Allow approximately 50 – 75 sq. ft. for rough concrete and 75 – 100 sq. ft. for smooth concrete.

    Wet-out concrete surface with fresh, clean, uncontaminated water . Wet-out the concrete with fresh, clean, uncontaminated water so the concrete is uniformly wet, without any standing or ponding water. The concrete must stay wet until the acid solution is applied.

    Apply acid solution uniformly . Apply acid solution uniformly over the wet surface of the concrete. The use of a plastic watering can will enable you to make sure fresh acid is applied evenly over the surface to be etched. ( DO NOT take a bucket of acid and dump it over the floor and spread it around with a broom. It will roll over the area and will neutralize as it spreads out giving an uneven etch to the surface of the concrete.) Applied properly to a clean surface the acid will begin to bubble indicating that the acid is reacting with the concrete. (If the acid fails to bubble on all or parts of the floor it means that the surface wasn’t cleaned thoroughly enough and must be cleaned and etched again.) Use a stiff bristle brush to scrub the acid into the surface and remove the layer of concrete to create the profile needed to apply the coating system.

    Allow acid time to react: 2 – 10 minutes . Allow the acid to remain on the surface of the concrete until the bubbling stops, usually between 2 – 10 minutes. Do not allow any areas of the etched concrete to dry out dry out during this time.

    Rinse / scrub surface . When the bubbling of the acid on the concrete surface slows noticeably, flush the concrete thoroughly with plenty of water while scrubbing the surface with stiff bristle brooms to remove the powdery residue from the pours of the concrete. This process may need to be repeated more than once to properly rinse the concrete. Collect and dispose of the liquids according to local and national regulations. After the floor is dry any powdery residue that remains on the concrete must be removed before applying the coating system.

    Check profile. Should be between 80 grit – 120 grit open coat aluminum oxide sand paper. Check the profile of the concrete surface. It should be the roughness of 80 grit – 120 grit open coat paper. The concrete must have a uniform open / porous surface before application of the coating system. The surface must be etched until this is achieved. More than one etch may be required.

    8 . Check the pH (ideal pH is 7.0, but 7.0-8.5 is acceptable.) Neutralize surface if necessary.

    Rinse / scrub surface. After the final rinse check, the pH of the wet surface. The ideal pH is 7.0, (neutral) but a pH of 7.0-8.5 is acceptable for most coatings unless otherwise specified. If the pH is below 7.0, residual acid in the concrete surface must be neutralized. One cup of household ammonia per gal. of fresh water will usually neutralize the concrete in one application.

    Apply solution uniformly over the surface. Let stand for 10 minutes before flushing and scrubbing with distilled water. Re-check the pH and repeat if pH is below 7.0. Use indicators such as pH strips, pH pencils, or Phenolphthalein solution. Once you have reached your desired results, make sure floor is totally dry before applying coating system.

    REMEMBER: After etching, examine the concrete for uniformity. The concrete texture should be similar to a CSP1, in accordance with ICRI (International Concrete Repair Institute). The surface should be free of surface glaze, laitance, salts and loosely adhering material. Sometimes, more than one etched may be required. Reference ASTM D4260, Standard Practice for Liquid and Gelled Acid Etching of Concrete. For the best performance from a coating system, concrete must be clean and have a uniform open / porous surface before application.

    Related Articles

    Acid-etch stain concrete products enable you to turn your boring gray concrete slab into a colored concrete floor. The products available today let you create patterns like those that you find in nature. You can create stained concrete floors that mimic the look of leather, wood or marble. Acid-etch products are suitable for both indoor and outdoor use.

    How Acid-Etch Stains Work

    Acid-etch stains contain water, acid-soluble metallic salts and hydrochloric acid. As you apply them to the concrete slab, the stains penetrate the surface and have a chemical reaction with the hydrated lime, or calcium hydroxide, in the concrete. The hydrochloric acid etches the surface of the slab, which enables the metallic salts to penetrate into the openings. The translucent, earth-tone colors of the stains are permanent. They allow the natural variations in the concrete to show through, just as wood stain allows the wood grain to show. No two concrete slabs take on the stain the same way.

    Preparation

    You need to remove any concrete sealer from the surface of the slab to make it easier for the concrete to accept the stain. If you splash water on the concrete and water beads, it means there’s sealer in place. The floor must also have all the soil and grease scrubbed off. A floor buffer can help you quickly clean the floor. Patch the floor before you stain it, but be sure to pick a product that accepts stain. Otherwise, you might be able to see the patch. As you prepare the floor, keep in mind that any marks on it will show through the stain. A final rinse of clean water is the last step in preparation for acid etching. Allow the floor to dry completely.

    Staining

    It’s possible to apply concrete stain with a brush or a sprayer. Both have their drawbacks. A brush can leave permanent marks in the floor, which you may not want. The acid can eat through metal parts in sprayers, causing issues with the way that they spray as well as the color of the stain. A good method is to apply stain with a sprayer that has nonmetallic parts. After you apply the stain, have a helper follow behind with a medium-bristle brush. He should work the stain into the concrete with circular strokes. Follow up with a second light coat of stain to remove the brush strokes. You can use stain full strength or dilute it with water. It’s possible to layer two or three colors of stain together to create one-of-a-kind overlays.

    Neutralizing and Sealing

    You must remove the acid that remains from the etching process from the concrete’s surface. A scrubbing machine makes short work of the task. Fill the scrubbing machine’s tank with detergent and water. Add 1 tablespoon of baking soda per gallon of water in the scrubbing machine to serve as a neutralizer. You must use soft buffing pads on the machine or you risk leaving marks on the unsealed concrete. Rinse the slab well with clean water and dry it with a wet-dry vacuum. Even if the surface appears dry, let it set for two days before applying a concrete sealer. Pick a solvent-based sealer for outdoor use and an acrylic, urethane or epoxy for indoor slabs. Sealers can provide a high shine to the finished slab, or they can have a softer finish.

    How to acid etch concrete

    The following is only a suggested guide on acid etching concrete for the application of thin film coatings such as Epoxy and Polyurethanes. Contact Gulf Coast Paint Mfg. for more detailed information on Surface Preparation on concrete surfaces.

    CAUTION: Acid etching requires the use of strong chemicals. Used improperly these chemicals can result in severe injury. When handling harmful chemicals, always wear protective clothing, protective eyewear/face shield, rubber gloves and boots. Do not breathe vapors.

    Always add acid to water. Never add water to acid!

    Protect surfaces not to be etched from chemical vapors, splash and spill.

    Dispose of all residual material according to local and national regulations.

    Scope: Acid Etching of Concrete for the Application of Coating Systems

    Properly clean the concrete surface first before acid etching the floor.

    Properly mix acid solutions.

    Wet-out concrete surface with fresh, clean, un-contaminated water. (No ponding)

    Apply acid solution uniformly.

    Allow acid time to react: 2 – 10 minutes.

    Check profile. Should be between 80 grit – 120 grit open-coat sand paper.

    Check the pH (ideal pH is 7.0, but 7.0-8.5 is acceptable). Neutralize surface if necessary. Rinse/scrub surface.

    Properly clean concrete surface. Remove all dirt, dust, grease, oils, wax, release agents or any other contaminants that will interfere with the acid etching and preparation of the concrete the concrete surface. Mechanical cleaning with stiff bristle brushes by hand or machine will be required for cleaners to work properly. Some contaminants such and sealers and curing compounds may not be removed by cleaning and will require the surface layer of the concrete to be removed by mechanical means. (Shot blasting, sanding, grinding, or any other approved method to remove the contaminant.)

    Before the acid etching process begins Gulf Coast Paint recommends several tests:

    Confirm new concrete is cured 28 days.

    Confirm that a vapor barrier was installed.

    Check for moisture following these 2 test methods that are most commonly accepted in the industry: ASTM 1869 (Calcium Chloride Test) and ASTM 2170 (RH Probe Test) .

    Complete a water dissipation test on random areas of the floor to determine that the proper degree of porosity has been achieved.

    Properly mix acid solution . Acids that can be used to etch the concrete are, muriatic, sulfuric, phosphoric, or citric. The most commonly used are muriatic (hydrochloric-HCL) and phosphoric acids. Use only plastic or acid resistant containers for mixing and applying acid. Acids concentrations can vary. To determine the strength and concentration to use to etch the concrete, test with a very dilute solution then add acid to container until strong bubbling action is noted in the test. Allow approximately 50 – 75 sq. ft. for rough concrete and 75 – 100 sq. ft. for smooth concrete.

    Wet-out concrete surface with fresh, clean, uncontaminated water . Wet-out the concrete with fresh, clean, uncontaminated water so the concrete is uniformly wet, without any standing or ponding water. The concrete must stay wet until the acid solution is applied.

    Apply acid solution uniformly . Apply acid solution uniformly over the wet surface of the concrete. The use of a plastic watering can will enable you to make sure fresh acid is applied evenly over the surface to be etched. ( DO NOT take a bucket of acid and dump it over the floor and spread it around with a broom. It will roll over the area and will neutralize as it spreads out giving an uneven etch to the surface of the concrete.) Applied properly to a clean surface the acid will begin to bubble indicating that the acid is reacting with the concrete. (If the acid fails to bubble on all or parts of the floor it means that the surface wasn’t cleaned thoroughly enough and must be cleaned and etched again.) Use a stiff bristle brush to scrub the acid into the surface and remove the layer of concrete to create the profile needed to apply the coating system.

    Allow acid time to react: 2 – 10 minutes . Allow the acid to remain on the surface of the concrete until the bubbling stops, usually between 2 – 10 minutes. Do not allow any areas of the etched concrete to dry out dry out during this time.

    Rinse / scrub surface . When the bubbling of the acid on the concrete surface slows noticeably, flush the concrete thoroughly with plenty of water while scrubbing the surface with stiff bristle brooms to remove the powdery residue from the pours of the concrete. This process may need to be repeated more than once to properly rinse the concrete. Collect and dispose of the liquids according to local and national regulations. After the floor is dry any powdery residue that remains on the concrete must be removed before applying the coating system.

    Check profile. Should be between 80 grit – 120 grit open coat aluminum oxide sand paper. Check the profile of the concrete surface. It should be the roughness of 80 grit – 120 grit open coat paper. The concrete must have a uniform open / porous surface before application of the coating system. The surface must be etched until this is achieved. More than one etch may be required.

    8 . Check the pH (ideal pH is 7.0, but 7.0-8.5 is acceptable.) Neutralize surface if necessary.

    Rinse / scrub surface. After the final rinse check, the pH of the wet surface. The ideal pH is 7.0, (neutral) but a pH of 7.0-8.5 is acceptable for most coatings unless otherwise specified. If the pH is below 7.0, residual acid in the concrete surface must be neutralized. One cup of household ammonia per gal. of fresh water will usually neutralize the concrete in one application.

    Apply solution uniformly over the surface. Let stand for 10 minutes before flushing and scrubbing with distilled water. Re-check the pH and repeat if pH is below 7.0. Use indicators such as pH strips, pH pencils, or Phenolphthalein solution. Once you have reached your desired results, make sure floor is totally dry before applying coating system.

    REMEMBER: After etching, examine the concrete for uniformity. The concrete texture should be similar to a CSP1, in accordance with ICRI (International Concrete Repair Institute). The surface should be free of surface glaze, laitance, salts and loosely adhering material. Sometimes, more than one etched may be required. Reference ASTM D4260, Standard Practice for Liquid and Gelled Acid Etching of Concrete. For the best performance from a coating system, concrete must be clean and have a uniform open / porous surface before application.

    How to acid etch concrete

    Acid washing vs Acid staining

    First, let’s clarify something: acid washing concrete or cement is quite different than how to acid stain . Although these terms are often confused, they have two different uses and outcomes.

    “Acid” when referring to concrete usually means muriatic acid or hydrochloric acid. This type of acid is used to etch or ‘burn’ into cement based surfaces. It can be used on its own or as part of a coloration system called acid stain.

    Acid washing is the means of using acid to etch and prepare a cement surface for painting or the application of some type of coating. Acid is usually mixed with water and then applied to the surface of the concrete and scrubbed in. This will etch and roughen the surface so that a coating or topping will adhere to its surface. Generally this will leave no decorative color or finish behind. Acid washed or acid etched surfaces can leave some level of white staining or residue which can be very difficult to remove. It is important to work in small areas and not allow the etched residue to dry.

    How to acid wash concrete

    If acid etching, the area to be prepared is hosed thoroughly, being careful to wet down any adjoining areas that may be damaged by contact with the acid solution. It is very important to keep the entire area wet until completion of the etching process. Never allow the acid solution to dry on the concrete as this could weaken the adhesion of the system.

    Etching is normally a two-man procedure, with one man operating the broom or floor machine (a nylogrit brush is used for etching) and the other man responsible for pouring the acid evenly and working the broom. The second man will also control the flushing of the area with the hose. The acid is mixed in a 5 gallon plastic pail – 3 or 4 parts water to 1 part acid. The strength of the solution is determined by the condition of the concrete. Very hard, smooth or shiny concrete will require a stronger solution.

    The acid solution is poured into a sprinkling can and then onto the surface. Hold the sprinkling can close to the surface to avoid splashing the acid on adjoining areas. Caution: the acid solution will permanently damage aluminum doors or painted metal surfaces. Keep adjoining outdoor carpet wet at all times and minimize contact with the acid solution. Do not get acid on concrete areas not to be etched. If contact does occur, flush as soon as possible with water.
    Five-gallons of mixed solution will cover approximately 150 sq. ft. The area will be scrubbed with the floor machine, systematically going first left to right, and then up and down. The second man will aggressively scrub the edges and places inaccessible to the floor machine. Use a stiff bristled broom or wire brush for this purpose. He will also work the hose to keep the area wet during the procedure.
    Upon completion of a 150 sq. ft. area, rinse well. A properly etched concrete surface has the profile of 80-100 grit sandpaper. If the concrete still feels smooth, repeat the procedure.

    After the concrete is thoroughly etched, pour 8 oz. APF Super Base Neutralizer into 4 gallons of water. Pour into the sprinkling can and disperse evenly over the area just etched. Scrub aggressively with the broom paying special attention to the edges and areas that may retain the acid solution (next to cabinets, washer and dryer, etc.). Rinse well.

    If it is necessary to walk on an area that has been etched and neutralized, be sure to hose boots off to avoid recontaminating the area. If the etched area was a driveway or garage, be sure to flush the residue well down the street. This is done with one man working the hose and the other brooming the residue until it is
    well dispersed.