Acid Etch - TechNote

Acid Etch - TechNote

Published by Bert Oey on Nov 12th 2020


Introduction: Proper surface prep is critical to product performance. New and existing bare concrete substrates should be cleaned and etched to ensure proper penetration and adhesion of BondTite 1101, AcryliSeal 3501 and other Wolverine Coatings Corporation products. Failure to achieve a clean properly profiled surface could result in poor finish and/or premature coating failure.

CAUTION:

Muriatic acid is strong enough to etch concrete, but it can also cause severe injury and/or damage property when used improperly.

  • Always wear protective clothing, rubber gloves, boots and goggles or a face shield when handling acid.
  • Avoid breathing acid vapors. Do not use in small confined areas. Have proper ventilation of fresh air! Use appropriate breathing apparatus if needed.
  • Make certain that the tools, clothing, containers etc. which may come in contact with the acid are acid resistant.
  • When combining acid and water always slowly add the acid to the water; never add water to the acid.
  • Protect all surfaces not being etched from accidental splashes or spills by masking off these areas.
  • Leftover acid should be disposed of in an approved manner and according to local regulations.
  • When using baking soda or bleach to neutralize acid, never add these materials to undiluted muriatic acid as a dangerous chemical reaction could occur.
  • Keep the work area clean and uncluttered.
  • Keep children and animals away from the work area at all times
  • Have plenty of clean water and baking soda available to rinse skin and eyes in case of an emergency.
  • Carefully read and follow all package warnings and precautions.
  • Basic Cleaning: All dirt, oil, grease, wax, dust, paints or other contaminants should be removed prior to etching the concrete. Oil and grease stains can be removed with a good quality oil stain remover. Dirt, grime and other debris can be removed by pressure washer and scrubbing with a good concrete cleaner. Curing agents, paints, or sealers should be removed by chemically stripping or mechanical means using a floor grinder, or in extreme cases a shot blaster or scarifier.
  • New Concrete: New concrete should cure a minimum of 28 days.

  • Etching solution

  • Type of Acid: Out of the variety of acids available for etching concrete (muriatic, sulfamic, phosphoric, organic salts or citric), muriatic (hydrochloric) and phosphoric acids are most readily available and effective. Muriatic acid, also known as hydrochloric acid, should only be used where chlorides are permitted.
  • Container/Acid Ratio: Acid resistant containers (plastic) should be used for mixing and spreading acids. It is essential to calculate the dilution of acid to water since acid comes in various strengths (usually 28 – 36%) and concrete floors react differently with some needing stronger acid solutions than others.
  • Determining Acid Strength: The best method for determining muriatic acid concentration is to test the substrate with a small, very dilute solution. Try starting with a 3:1 solution, that is 3 parts water mixed with 1 part acid. Apply the solution to a test area, you want to see the solution cause a bubbling action on the concrete. If the solution shows no reaction decrease the amount of water, if the solution has a strong reaction with visible fumes, it’s too strong, add more water to your mixture. Adjust the mixture of acid and water until you determine the correct balance of acid concentration needed for your concrete. Note: On some floors different areas may require different strength solutions. One gallon of the acid mixture should be allowed for each 50-75 sq. ft. of rough concrete or each 75-100 sq. ft. of smooth concrete.

  • Dampen the Concrete:

  • The concrete surface should be pre-wet with clean, potable water. The substrate should be uniformly wet without any puddling or standing water. The concrete should remain wet until the acid solution is applied and neutralized.

  • Apply the Acid Solution:

  • Application of the Acid: The acid solution should be applied uniformly over the surface of the concrete. A good way to apply the acid solution is with a plastic garden sprinkling container. The acid/water mix should be applied in an even manner over the entire surface so the etching results will be uniform. The acid solution should not be poured onto the floor and swept over the surface, doing so will result in uneven results. The acid solution should begin bubbling indicating a correct reaction with the concrete. The acid solution should be scrubbed thoroughly with a stiff bristled brush during the application process. If some areas aren’t bubbling as much as the rest of the floor, agitate them with extra broom scrubbing.
  • Any areas that just refuse to bubble could mean the area has contaminates that are preventing the acid from reaching the concrete. It will be necessary to properly clean and re-etch or prepare these areas by mechanical means.


    Allow Acid time to React:

  • The acid solution should be allowed to remain on the concrete as long as the bubbling continues (usually about 2-10 minutes, although the time depends on floor conditions and acid concentration). The floor should not be allowed to dry out during the acid etching process!

  • Neutralize and Rinse the Concrete:

  • When the bubbling action of the acid solution slows down, using the garden sprinkling container flood the area with a generous amount of a solution of two pounds of baking soda in five gallons of water to neutralize the acid and then repeatedly flush with clean water. DO NOT USE HIGH PRESSURE POWER WASHER. Check with your municipality for guidance on proper disposal of all liquids. Use a wet vac if needed. The surface should have a uniform texture of medium grit sandpaper, if not; the acid etching process must be repeated. When proper texture is achieved the substrate should be flushed two or three times with fresh water while scrubbing with a stiff bristle broom in order to remove any existing powdery residue. To avoid possible adhesion failure, vacuum any residue or white powder after the surface is dry (before applying coatings).
  • If muriatic acid is used for etching, check the pH of the final rinse water on the wet concrete with pH test strips. An ideal pH reading is 7.0 (neutral); however, a range of 6.0-9.0 is usually acceptable for most coatings, unless otherwise stated. A pH range below 6.0 would indicate acid residue remains in the pores of the concrete and must be neutralized. A strong ammonia solution or two pounds of baking soda in five gallons of water will generally neutralize the concrete in one application. The neutralizing solution should be spread uniformly over the substrate in the same manner as the acid solution. The surface should remain wet with the solution for at least ten minutes before agitating and flushing with water as recommended when etching the substrate. The pH should be checked and the neutralization process repeated if the pH of the rinse waster is still below 6.0. For a pH reading over 9.0, repeat the rinsing process until the pH is at an acceptable level.
  • Do not use high pressure water such as power washers for the initial neutralizing rinse/s. Instead, flush the concrete with your garden hose at regular city water pressure. Once rinse water pH has been confirmed to be within acceptable range then high-pressure water stream can be used but, be careful as it can leave deep scars that may not completely fill when coatings are applied.

  • Dry the Concrete before coating:

  • Use a shop vacuum suitable for wet work, a floor squeegee, or stiff broom to remove all standing water from the floor.
  • Use an electric leaf blower or reverse shop vacuum to blow water out of joints and cracks.
  • If you use an air compressor to blow out water and moisture, make sure that the pressurized air is oil free and that no compressor oil or other containments are blown onto the floor!
  • Warm, dry, clean air blown over the surface will speed up the drying of the concrete. Using fans, opening doors and windows, will help speed up the dry time.
  • In-floor heating and other heat sources will help speed up the dry time, however when using heaters make sure they do not discharge any moisture, fuels, oils, lubricants, or soot that may contaminate the floor. Direct fired heat sources such as unvented propane or NG heaters produce carbon dioxide which can absorb into bare concrete substrates and will adversely affect curing epoxies and urethanes.
  • Unlike most epoxy coatings BondTite 1101 does not require the concrete to be “bone dry” before application. There should be no standing water at all, and the floor must not be overly moist. Usually when the concrete starts to lighten up and look dry the floor is dry enough to be coated with BondTite 1101.
  • Conclusion:

    The method of etching is not as important as the end result. A properly etched surface should have a pH level close to 7.0, be clean and have the texture of 100 grit sandpaper which allows our products to mechanically and chemically bond to the substrate.

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