CREATING UNIQUE CONCRETE FLOOR DESIGNS 
WITH ACID ETCHING

According to many home improvement shows and magazines, the newest hot trend for flooring is acid etching.  This is a process where a special type of acid, usually muriatic acid is applied to clean concrete surfaces.  However, muriatic acid is actually undiluted hydrochloric acid, and is extremely dangerous to use, therefore you must read and follow all manufacturer’s instructions carefully.  

You can purchase special stains that are available in an array of colors ranging from blues, green, to reds browns and just about every color and shade between with many being natural shades.  However, it is important to understand that you can purchase the same lot number, use it on two different concrete surfaces, and have two different variations of the color.  This is because the stains will react differently to the compounds in the concrete, which will produce variegated, marbleized, or stone-effects.  This uniqueness is one of the great appeals of stained concrete flooring, with its other advantages being its endless possibilities of designs, its durability, and ability to retain its beauty even in heavy traffic areas.  In addition, acid etching is very reasonable, costing approximately $0.25 per square foot to $1.00 per square foot, depending on the preparation required and the materials you use.

The first acid-etched concrete floor that I installed was in my best friend’s sunroom.  Believe me it was remarkably easy. 

The first concrete floor that I acid etched was a 6-inch solid concrete slab of my friend’s 16 x 20 foot sunroom.  The floor originally had indoor-outdoor carpet, and she’d had seen a do-it-yourself show and wanted to attempt acid etching.  However, her husband did not want us to score the concrete with a saw to form the design into the concrete.  Therefore, we did our research and found that we could us tape to form the grout lines. 

IMPORTANT: When using concentrated acid you should always handle it with care.  You need to wear protective clothing that includes rubber gloves, rubber boots, and protective eyewear.  When diluting the acid, always add the acid to the water.  NEVER add water to the acid as this can result in an explosive chemical reaction that can cause you personal harm. 

Once we removed the old indoor-outdoor carpet, we had to clean thoroughly the concrete surface to remove all contaminants, which may have interfered with acid etching and stain that we would use.  You can remove dirt, oil, grease, and most other petroleum-based contaminants with a good Oil and Grease Emulsifier.  If you are etching a newly poured concrete floor, laitance may be present.  Laitance is a thin layer of non-durable concrete. 

After you have cleaned, scrubbed, and squeegeed the concrete floor, allow the floor to dry.  Next, you need to lay down masking tape, which will simulate the grout lines.  You have to make sure that the tape is firmly placed down; we went back over the tape with a wallpaper roller.

Once you have applied the tape, you want to spray on the acid wash stain.  In the sunroom, we used spray bottles to apply the diluted acid wash stain.  However, on a later project we discovered that a large garden sprinkler-can also works nicely.  Make sure that you leave the acid solution to stand on the floor for the recommended amount of time before you rinse, rinse, and rinse some more.  We rinsed the surface four times for the first coating and six times after the second application.  You will notice a brownish colored residue forming during the etching process.  This residue must be scrubbed off.  We applied two acid wash stain coats. 

It is very important that you thoroughly rinse, using plenty of clean, fresh water.  If you do not rinse well enough you risk leaving unspent acid salts on the surface of the floor, which can interfere with both the curing and adhesion of the coating.  In addition, residual acids can also affect the long-term durability and performance of the coating.  You can neutralize the acid wash using by sprinkling baking soda over the floor if you are sure that you have rinsed the floor well enough.  After the final rinse, allow the floor to dry before sealing the floor.