Acid Etch Tips

Acid Etch tips

Proper surface preparation is critical to our three component epoxy coating performance. New and existing bare concrete substrates need to be cleaned and profiled to ensure proper penetration and adhesion of BondTite 1101, AcryliSeal 3501 and other Wolverine Coatings Corporation epoxy products. Failure to achieve a clean properly profiled surface could result in poor finish and/or premature coating failure. For those who choose to etch rather than grind we offer the following Acid Etch tips.

At AlphaGarage we consider mechanical grinding to be the best preparation method for our epoxy systems due to its ability to both open the concrete pores as well as produce a consistent and proper surface profile. At the same time, we understand that there are circumstances which preclude the use of mechanical grinding so acid etching may be a viable alternative. Proper acid etching will accomplish the task of opening up concrete pores but typically cannot produce the optimum surface profile that mechanical grinding can produce.

There are alternative etching chemicals available that will perform similar to muriatic acid so please make sure to follow their specific instructions. The following information applies to the use of muriatic acid.

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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 available to rinse skin and eyes in case of an emergency.
  • Carefully read and follow all package warnings and precautions.

General Surface Preparation:

  • Basic Cleaning: All dirt, oil, grease, wax, dust, paints or other contaminants need to 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, shot blaster or scarifier.
  • Concrete: Any surface imperfections should be removed by mechanical means. Expansion and construction joints, cracks, holes and other voids should be filled with appropriate fillers. See our TechNotes for additional instruction.
  • New Concrete: New concrete should cure a minimum of 28 days and moisture content should be measured at less than 12% prior to painting, sealing or staining. See our TechNotes for additional instruction.

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.

REMEMBER: always add the acid into the water NOT water into 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:

• Pre-Wet 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. Note: The area being treated should be done in small sections so the pre-wet concrete does not dry out before applying and working the acid and so that the acid solution does not dry on the concrete before you’re ready to neutralize and rinse.

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). The floor should not be allowed to dry out during the acid etching process!

Rinse the Concrete:

• When the bubbling action of the acid solution slows down, spray the area with a generous amount of water or first spray a solution of one pound of baking soda in five gallons of water to neutralize the acid and then flush with water. For proper disposal of all liquids, use a wet vac if no drains are present. The surface should have a uniform texture of medium grit sandpaper, if not; the acid etching process must be repeated. The substrate should be flushed two or three times 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 coating).

Neutralize the Concrete as Required:

• If muriatic acid is used for etching, check the pH of the final rinse water on the wet concrete with pH paper. 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 re-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.

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 a 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 it’s oil less or otherwise properly filtered to ensure that no compressor oil or other containments are reintroduced 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 fuels, oils, lubricants, or soot that may contaminate the floor.
  • VERIFY absorption! Once the floor has been allowed to dry utilize the “water droplet test” outlined on page 2 of the Application Instructions to verify that the surface will be able to absorb the epoxy. If there are areas that do not readily absorb moisture additional etching or mechanical grinding may be necessary.
  • Unlike most epoxy coatings Wolverine 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 moist. Usually when a few sections of the concrete start 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 be clean, have a texture approximating that of 80 grit sandpaper and exhibit uniform moisture absorption. which would allow our BondTite 1101 to mechanically and chemically bond to the substrate.

For additional information please contact us.

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