How to acid etch concrete

The lifespan of a coating or overlay party depends on its adhesion to the concrete surface. If it does not adhere properly, it will flake and chip off. Although it is common to blame the coating for being low-quality, it is actually the concrete that failed. Concrete may contain laitance or contaminants that hinder a coating from supposedly sticking on the surface. This is why it is important to prepare the surface well prior to resurfacing. Professional concrete contractors know that surface preparation phase is the most crucial parts of the job. One way to make the concrete ready is by acid etching.

What is Acid Etching?

How to acid etch concreteAcid etching is the process of neutralizing a concrete surface through the use of muriatic or phosphoric acid. The acid is applied on the concrete and then rinsed off with water. This has been the standard method for preparing the concrete slab for a coating or overlay. However, the debate on whether it is still acceptable to do is confusing homeowners. Should it be done or not?

Advantages of Acid Etching

  • Acid etching is used to extrude and fabricate concrete
  • It is effective in reducing the color variation, creating a more uniform color
  • Etching can be used to smoothen out a concrete surface
  • It opens the pores of a concrete slab, enhancing adhesion
  • Less labor-intensive method than grinding or sandblasting

Disadvantages of Acid Etching

  • Results are inconsistent since not all concretes are the same
  • It can damage the concrete slab when it is over-etched or under-etched
  • Since an acid is used, it is dangerous for both humans and the environment
  • It adds unnecessary costs to a project and affects the time frame of the project

Safer Alternatives to Acid Etching

How to acid etch concreteThere are safer alternatives to acid etching today. Most concrete contractors are no longer recommending acid etching because of its effect on health and the environment. Instead of etching, sandblasting or grinding is a great way to remove any contaminants on the surface of the concrete slab and to open its pores as well.

If you should have concrete work done in your property, make sure to choose a contractor who uses a safer yet effective surface preparation method. It is important to ask them how they plan to prepare the surface. If they mention acid etching, ask if they could use an alternative method instead. Better yet, find another concrete contractor to work with.

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How to acid etch concrete

Acid etching is a process that uses a strong acid to cut into another substance. It is used for both industrial and artistic purposes. For example, etching can be used to prepare flooring like cement for painting or refinishing, while artists use it to create detailed pictures on metal or glass.

In acid etching of concrete, chemicals like muriatic acid, phosphoric acid, or sulfamic acid are used to prepare flooring to accept epoxy paint. Floors must be clean, and users must proceed with extreme caution as the acids used can be very dangerous. The acid is prepared as a liquid solution that is brushed over the floors, and then cleaned off before paint is applied. This process is typically used by home owners to finish and protect flooring in garages, basements and shops in the home.

In artistic metal acid etching, a metal sheet is covered in a waxy substance called a ground. The artist uses precision tools to create designs in the wax. The sheet is then dipped into an acid bath, which etches, or eats into, the areas where the metal has been left exposed. Once the acid has etched the exposed metal to the desired depth, it is removed from the bath and the ground is cleaned off. The etching can then be used with ink to produce identical paper images in much the way that a printing press does.

A similar acid etching process can create glass etchings as well. A “resist,” usually made of wax, or a similar sticky substance, is placed on the glass where the natural color is to remain. The glass is then dipped into a hydrofluoric acid bath, after which the resist is removed and the etched image will be visible. This process is extremely dangerous, however, so the average home craft enthusiast will often choose a much safer etching cream for small home projects on glass. A stencil is placed on the glass and etching cream is wiped over the stencil leaving behind a cloudy pattern. Although they are sometimes confused for acid etchers, these etching creams do not eat into the glass for a permanent etch like hydrofluoric acid does.

Photo acid etching is an offshoot of metal etching. Instead of using a ground, an image is printed onto special paper to produce a photo resist that is then placed on the metal. The sheet is then exposed to light to place the image onto the metal. The sheet is then dipped into the acid bath and the image is etched into the metal. A light etch can produce a plate similar to a standard metal etching, while a deeper etch can make it possible to literally punch the image out of the metal for metal models, or various types of decorations.

The longevity of a coating partly depends on how well it adheres to the surface of the concrete. The best adhesion requires a clean floor, free of laitance and contaminants.

Laitance is a weak, milky accumulation of fine particles of cement dust, lime and sand fines on the surface of fresh concrete, usually caused by an excess of water bleeding to the surface.

What Is Etching Concrete

Acid etching is the process of applying hydrochloric/muriatic or buffered phosphoric acid to a slab, then rinsing it off with water. For many years, it was a standard method of concrete preparation used by nearly all industrial, commercial and institutional floor coating installers, depending on the floor size and system to be installed.

Today, safer, eco-friendlier and more consistent concrete prep methods are the norm. Most coating manufacturers no longer recommend acid etching for a multitude of reasons.

Acid Etching Results Are Inconsistent

Acid etching removes laitance, but cannot remove curing compounds or many of the contaminants found in industrial settings, such as oily deposits and water-insoluble materials, any of which can interfere with the adhesion of a coating.

How to acid etch concrete

Improper surface preparation can result in poor bond and lack of coating adhesion.

Additionally, because every slab is different, the results can be unpredictable and unreliable, even when the process is done by experienced professionals. The surface can end up uneven, over-etched, or under-etched.

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Acid Etching Concrete Creates Only a Minimal Profile

Concrete Surface Profile, or CSP, as defined by the International Concrete Repair Institute (ICRI), is a standardized measure for the ‘roughness’ of a given concrete surface. This can range from CSP-1 (smoothest) to CSP-9 (roughest). The thicker the coating system, the higher the required CSP number.

Acid etching tends to produce a CSP-1 to CSP-2 profile, which is suitable for only for very thin systems, such as the low solids, solvent-based coatings of the past. Today’s low emissions and solvent free industrial, commercial and institutional resinous flooring systems tend to be much thicker, requiring CSP-3 to CSP-9 for best bond and performance; this essentially renders acid etching obsolete. Contractors look to mechanical concrete preparation, such as diamond grinding, shot-blasting and scabbling to create the higher CSPs needed.

How to acid etch concrete

The right concrete prep is the foundation for flooring success, like this cheerful FloroThane MC System in a custom yellow, skillfully installed by Florock UK.

Acid Etching Can Damage the Slab

The chemical reaction that occurs when an acid solution is applied to concrete is difficult to accurately predict and control. When applied to the surface, over-etching can easily occur, often making the surface more porous. When the acid is finally rinsed from the surface, the water can more easily enter the porous slab, resulting in potential corrosion of metal rebar and eventual weakening of the entire slab structure.

What does Etching Concrete do to Humans and the Environment

It is not surprising that any physical contact with certain acids can cause chemical burns or other injuries. Lesser known, however, is that even inhaling the fumes from concentrated muriatic acid is extremely dangerous, because it can turn the moisture in the windpipe and lungs into a virtual acid solution. Even with safety equipment, the risks remain significant.

Clean rinse water is introduced to the floor after the etching reaction is completed. This neutralizes the acid solution to a certain degree, provided the rinsing is done correctly. Nevertheless, many local and federal agencies have imposed restrictions on washing the solution (“neutralized” or not) down the floor drain, due to the risk posed to waterways and the environment as a whole.

Acid Etching Can Add Time and Cost to a Project

Regulations for warehousing and shipping high concentration acids involves multiple safety measures and extensive paperwork, thus increasing cost on etching products.

Finally, acid etching introduces water to the concrete, which is best avoided with many of today’s zero V.O.C. and ultra-high solids coatings. Once the substrate is saturated, the contractor must then decide to either wait any number of days for the slab to completely dry or choose a moisture tolerant primer that may add cost to the project. Prepping via mechanical means, rather than acid etching, can be much faster and far more economical.

Our Network of Technical Experts

At Florock, our mission is to give you the best possible solution to meet your facility needs. Our network of experts understands the ins and outs of concrete preparation and its effects on the life of your resinous flooring system, and will work with you to help ensure you receive optimal flooring value.

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.

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 Concrete: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 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.

    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.

    Published Friday 16th of July 2021 // Updated Tuesday 8th of June 2021

    Please refer to manufacturer Safety Data Sheets (SDS) and Technical Data Sheets (TDS) before using any acidic product for detailed explanations of how to safely use.

    It’s always recommended to wear the appropriate Personal Protective Equipment (PPE) when acid etching. PPE such as safety glasses, gloves, and respirators are recommended as needed. If you have questions about appropriate PPE for your project do not hesitate to call us.

    Proper concrete etching is a REQUIREMENT for all Sani-Tred floor installations on the original surface. Acid etch procedure MUST be followed exactly as specified below for proper installation. Sand blasting, captive ball blast or scarifying the concrete floor surface is always preferable to acid etching when ever possible.

    • Make sure the substrate is clean and free of any previous applied products and other bond breaking contaminants, sealers, etc…
    • Reduce Muriatic Acid (same as hydrochloric acid) with water to a 10% solution. Apply the acid etching solution over the concrete and agitate using a push broom until foaming action stops. (Follow manufacturer’s instructions)
    • Rinse with warm water (ideally) or with a pressure washer
    • Mix Apply a “neutralizing solution” over the concrete
    • Rinse with water

    The purpose for acid etching is to remove “latencies” from the surface of concrete floors. When a floor slab is poured, contractors etc often float or trowel the surface smooth by working up a smooth weak film over the concrete surface, this weak film is called “latencies”.

    Never acid etch concrete walls, unless the concrete was troweled by hand. Acid etched concrete floors will provide an approved surface in which to produce a penetrating and permanent bond for the Sani-Tred products. While this treatment is effective on new concrete, it may not be completely effective on old concrete with oil, grease, fats, or other bond-breakers present, unless it is properly prepared.

    Before any floor coating is applied to concrete, remove ANY previous applied products, sealers, contaminants, bond breakers, etc. The concrete should always be prepared properly in order to allow a penetrating and permanent bond of the Sani-Tred products. The bond, durability, and service life of any floor surface material relies on proper concrete surface preparation. Previously applied paints or coatings may usually be removed using our “Off The Wall Coating Remover” which is available from SANI-TRED, then washed and acid etched.

    Muriatic (Hydrochloric) acid is normally available from local hardware stores, lumber companies, swimming pool supply, chemical companies, etc… at a 31% to 37% concentration that MUST be diluted with additional water to bring it to a 10% solution. If the “acid etch mixture” is not properly mixed at a 10% solution, the solution will be to weak to properly remove concrete latencies or it may be too strong and etch the surface deeper than necessary, and soak into the concrete surface and contaminate it with a destructive, lingering, acidity after floor materials are applied. Never use “straight acid” mixtures for this reason. Muratic Acid is typically packaged at a 30% dilution (be sure); you want to dilute it down to a 10% dilution (1 part acid to 2 parts water).

    The acid etching solution can be poured out, distributed using a squeegee, and agitated the surface using a push broom. Keep the acid etch solution on until it stops foaming. When the acid etch solution stops foaming you can begin rinsing. If the acid mixture does not “foam” evenly over the entire surface of concrete on which it is applied or simply “beads up” on the surface, then this is a sign that a foreign “bond breaker” is on the surface of the concrete. This could be concrete curing sealers, oils, grease, fats, silicone, paints, clear coats etc… If acid alone is used on a concrete surface with a bond breaker present, it will not acid etch the floor, will not remove oils, and will not remove coatings, sealers, etc… because acid is not a degreaser or a remover. Oils may only be temporarily “floated” above the surface, only to be re-deposited elsewhere when the floor dries. If the floor has large areas that are contaminated with oil, grease or other bond-breakers, they should be removed or decontaminated from the concrete surface.

    Rinsing Acid Etching Solution:

    Flush away the acid etching solution with warm water (preferably). One may remove acid etch solution with a shop vac, squeegee, rented water handling equipment, or pressure washer (ideally).

    Mixing and Applying Neutralizing Solution:

    Before neutralizing, it is best to choose which neutralizing solution would be best for your application. After acid etching and rinsing, the concrete should be neutralized otherwise the concrete will be left and acidic contamination which will inhibit PermaFlex from adhering permanently. One can neutralize with either of the following solutions:

    • 1 cup household baking soda per gallon of water, allow it to stand for at least 15 min., do not allow to dry. After rinsing, you can allow it to dry naturally or torch it dry and immediately begin the Sani-Tred application. Most often the best neutralizing solution to use.

    Rinsing Neutralizing Solution:

    Flush away the neutralizing solution with water. To do so, one may remove the Neutralizing Solution with a shop vac, squeegee, rented water handling equipment, or pressure washer and rinse the concrete with water.

    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.

    The lifespan of a coating or overlay party depends on its adhesion to the concrete surface. If it does not adhere properly, it will flake and chip off. Although it is common to blame the coating for being low-quality, it is actually the concrete that failed. Concrete may contain laitance or contaminants that hinder a coating from supposedly sticking on the surface. This is why it is important to prepare the surface well prior to resurfacing. Professional concrete contractors know that surface preparation phase is the most crucial parts of the job. One way to make the concrete ready is by acid etching.

    What is Acid Etching?

    How to acid etch concreteAcid etching is the process of neutralizing a concrete surface through the use of muriatic or phosphoric acid. The acid is applied on the concrete and then rinsed off with water. This has been the standard method for preparing the concrete slab for a coating or overlay. However, the debate on whether it is still acceptable to do is confusing homeowners. Should it be done or not?

    Advantages of Acid Etching

    • Acid etching is used to extrude and fabricate concrete
    • It is effective in reducing the color variation, creating a more uniform color
    • Etching can be used to smoothen out a concrete surface
    • It opens the pores of a concrete slab, enhancing adhesion
    • Less labor-intensive method than grinding or sandblasting

    Disadvantages of Acid Etching

    • Results are inconsistent since not all concretes are the same
    • It can damage the concrete slab when it is over-etched or under-etched
    • Since an acid is used, it is dangerous for both humans and the environment
    • It adds unnecessary costs to a project and affects the time frame of the project

    Safer Alternatives to Acid Etching

    How to acid etch concreteThere are safer alternatives to acid etching today. Most concrete contractors are no longer recommending acid etching because of its effect on health and the environment. Instead of etching, sandblasting or grinding is a great way to remove any contaminants on the surface of the concrete slab and to open its pores as well.

    If you should have concrete work done in your property, make sure to choose a contractor who uses a safer yet effective surface preparation method. It is important to ask them how they plan to prepare the surface. If they mention acid etching, ask if they could use an alternative method instead. Better yet, find another concrete contractor to work with.

    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

    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.