Acid etching is often used by individuals for surface preparation of home shops, garages, basements, etc.
If the concrete is contaminated with oils or grease, the first step is to clean the surface with an alkali detergent cleaner and commercial degreaser The recommended method is to use the detergent in combination with a steam cleaner. See DEGREASING section on our Surface Preparation Page.
1: HYDROCHLORIC (MURIATIC) ACID
Usually sold in 31% solutions. Dilute to 10%-15%. Use 1 gallon for every 40-50 square feet. A dangerous acid with VERY strong fumes.
2: PHOSPHORIC ACID
Used when the strong acid fumes can't be tolerated or around acid vulnerable metals such as carbon or galvanized steel. In these situations a solution of 20% - 40% Phosphoric Acid.
3: SULFAMIC ACID
A white powder dissolved in hot water. Much less dangerous to work with than the other acids mentioned above and the best choice for do it yourselfers (try Home Depot). Mix one pound of Sulfamic Acid with 1 gallon of hot water to treat 300 square feet of concrete.
PROCEDURE
1) Degrease and 'seal' contaminated areas (See DEGREASE section in our Surface Preparation Site). Sand, degloss, strip or remove existing coatings. Well bonded existing coatings can usually remain in place.
2) Clean floor with a detergent and rinse well.
3) Wet the floor with ordinary tap water. If the water beads up on the concrete, it could be potential problem area. After completing the surface preparation retest with more water. Do not attempt to coat the area if water still beads up.
4) Apply the acid solution in an even manner using a sprinkling can or acid tolerant pump spray unit.
5) Scrub the acid solution into the concrete with a stiff bristle broom or scubber.
6) Let the acid sit for 5 - 10 minutes.
7) Rinse or somehow remove the spent acid.
8) BEFORE the acid dries on the surface, remove residue with water hose or other high pressure water sprayer and vacuum up. Simply pouring water on the surface and wet vacuuming will not adequately remove the residue.
9) Neutralize any acid residue. Some people use diluted liquid bleach or household amonia for this (NOTE: bleach and acids can have a dangerous reaction. It is one thing to neutralize a slightly, well rinsed, acid floor with bleach. It is quite another thing to mix acid and bleach. Don't Do It! Follow with lots of rinse water. Others recommend a diluted "Simple Green" cleaner (4 oz per gallon of water). Checking with pH paper is a good idea! A bad acid rinse is probably worse than no acid etching at all.
10) An optional, but potentially very important step is to next wash the surface down with a 'mineral/acid salt remover. Salts on the surface of the concrete do not rinse off easily and can lead to adhesion problems as they absorb moisture becoming corrosive liquids and/or as their crystal structure grows. Although this step is not common, more and more painting contractors are learning about the problem of 'hidden salts' and are starting to use products like our salt remover. If you apply this product, it must be rinsed off well as it dissolves the salts.
11) Let the concrete completely dry and again sweep clean of any dust, dirt, and particles from the acid etching process.
