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 paints, sealers, stains or textured coatings.  Failure to achieve a clean uniformly porous surface could result in a poor appearance and/or premature coating failure.

General Surface Preparation: 

• Basic Cleaning:  All dirt, oil, grease, wax, dust, release agents 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, such as, Seal-Krete OSR.  Dirt, grime and other debris can be removed by pressure washer and scrubbing with a good concrete cleaner.  Curing agents or sealers should be removed by chemically stripping or mechanical means using a floor grinder or scarifier.

• New Concrete:  New concrete should cure a minimum of 30 days and moisture content should be measured at less than 12% prior to painting, sealing or staining the substrate.  Any surface imperfections should be removed by mechanical means.   Bug holes and other voids should be filled with appropriate filler.

• Painted Concrete:  Clean substrate as directed in General Preparation section.  Remove any loose or peeling paint by scraping, wire brushing or power washing.  Paint edges should be feathered by sanding as needed.  Small exposed areas should be wire brushed to remove any laitance or other contamination prior to priming with Seal-Krete Lock-Down.  Large exposed concrete areas should be treated as unpainted and etched as directed in etching section.   Widespread adhesion failure could indicate the need to completely remove the existing coating by power washing, power tooling, paint stripper or other means to ensure adhesion of the new coating.  If water intrusion has caused the previous coating failure, the problem must be corrected before recoating the substrate.  Sound, existing coatings should be prepared, as appropriate (lightly sanded, cleaned and primed), prior to painting.

Caution:

Keep in mind, an acid that is strong enough to etch a concrete surface could cause severe injury when used improperly.  Wear protective clothing, rubber gloves, boots and goggles or face shield, when handling acid. Avoid breathing acid vapors.  Always add acid to water.  Never add water to acid while in the process of diluting the etching solution.  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. 

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 normally the products of choice.  Muriatic acid, also known as hydrochloric acid, should only be used where chlorides are permitted.  Seal-Krete Clean-N-Etch is a combination of phosphoric acid and a cleaning agent. 

• 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 commercial containers may vary in concentration.  Typically, muriatic acid is usually mixed at a ratio of one part acid to three parts water in order to reach a required level to adequately etch bare concrete.  Phosphoric Acid, Seal-Krete Clean-N-Etch is mixed at one part acid/cleaner to one part water. 

• Determining Acid Strength:  The best method for determining muriatic acid concentration, is to test the substrate with a very dilute solution, then add acid to the container as required until a strong bubbling action is observed in the test.  This will confirm the amount of acid concentration needed for the project.  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 concrete does not dry out before applying and working the acid.

Apply the Acid Solution:

• Application of the Acid:  The acid solution should be applied uniformly over the surface of the concrete.  An excellent means of application is with a plastic garden sprinkling container.  The fresh acid should be deposited in a consistent manner over the entire surface so the etching results will be uniform. The acid solution should not be dumped onto the floor and swept over the surface.  Acid spread in this manner will be partially spent and will not yield uniform results.  The acid solution will begin bubbling indicating it is reacting to the surface layer of concrete.  Any areas failing to produce the bubbling action would indicate 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.  The acid solution should be scrubbed thoroughly with a stiff bristled brush during the application process.

Allow Acid time to React:  

• The acid solution should be allowed to remain on the concrete as long as the bubbling continues (usually 2-10 minutes, however, this would depend on the floor conditions and acid concentration used for the project).  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 painting).

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 Thoroughly before Painting:

• No matter what coating system is selected, it is important the moisture in the concrete is low enough that it will not affect the application, cure or performance of the coating.  An ideal moisture content would be below 12% for most coatings and below 15% for acrylic paints and sealers.  Should a moisture meter be unavailable, ASTM Test Method D 4263-83 should be followed to determine moisture content.  This is the Standard Method for Indicating Moisture in Concrete by taping sheets of minimum 4 mil thick polyethylene plastic, at least 18 by 18 inches square, onto the concrete with 2-inch wide duct tape.  A test patch should be applied for each 500 square feet of concrete.  These test patches should be allowed to remain in place at least 16 hours before removing to check for moisture on the back of the plastic and concrete area being tested.  This method is not an exact measurement of the moisture content; however, it will determine the relative amount of free moisture in the concrete and whether or not to postpone the coatings application.  Warm, dry air blown over the surface will hasten drying of the concrete.  Using fans alone will speed up the dry time.

Conclusion:

The method of etching is not as important as the end result.  A properly etched surface should be clean and have the texture of medium grit sandpaper which would allow immediate water penetration.  This will ensure the material being applied will bond to the concrete substrate.

Warranty:

The above information is based on available data and is believed to be correct.  We make no warranty, expressed or implied, regarding the accuracy of this information and assume no responsibility for injury from use of the product(s) herein described.