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CONCRETE CLEANING: CLEANING CONCRETE SURFACES EFFECTIVELY

Because of its porosity, concrete surfaces are easily stained.

Most of these stains can be easily removed. A few stubborn stains will leave traces. Stains should be removed as quickly as possible to prevent farther migration into the concrete. Also, time causes stains to bind more tightly to the concrete or to undergo a chemical change, making removal much more difficult.

The first step is to identify the stain and then choose a cleaning agent and cleaning method. If the stain is impossible to identify, cleaning methods and materials should be tested in an small out of the way area.

Removal agents should be used in the following order on unidentified stains:

(1) organic solvents, (2) oxidizing bleaches, like those based on peroxides or hypo chlorides, (3) reducing bleaches, some of which are used in an acidic medium, and (4) acids and other acidic materials.

TECHNIQUES FOR REMOVING STAINS:

Hot Water Washing: A hot water spray is recommended. If the water alone is not cleaning the concrete, it can be used in conjunction with the following in the order listed: a soft brush, a mild soap, a stronger soap, ammonia, or vinegar.

Chemical: Organic solvents can usually be used with little dilution. Inorganic solvents such as ammonium hydroxide, sodium hypochlorite, and hydrogen peroxide can be purchased in ready-mixed solutions; other organic solvents can be purchased as solids and then mixed with water according to manufacturer's directions. Acidic materials will etch the concrete surface. Saturating the surface with water before applying the acid solution and flushing it thoroughly after completing the cleaning reduces the amount of etching.

A concern with chemical cleaning is contamination from soluble salts. Some chemicals contain salts; others form salts through a reaction with the material being cleaned. A build-up of salts in the pores of concrete can damage it.

However, the heat can cause the concrete surface to scale off. Steam is especially good for removing chewing gum from paving; however, in most applications it is comparatively expensive.

REMOVING SPECIFIC STAINS:

Rust: If the stain is light or shallow, mop the surface with a solution of 1 lb oxalic acid per gal of water. Wait two or three hours, and then scrub the surface with stiff brushes while rinsing with clear water.

If the stain is deep, use a poultice. Mix 11 oz (by weight) sodium citrate and 2 qt lukewarm water. Add 2 qt 12 oz glycerol. Make a stiff poultice with diatomaceous earth or talc; trowel over the stain. Leave the poultice for 2 or 3 days. Repeat if necessary.

Oil: If the oil is freshly spilled, soak it up with absorbent paper; do not wipe it up. Cover the stain with a dry powdered material such as Portland cement, hydrated lime, cornmeal, or cat litter. Wait approximately 24 hours, then sweep it up. Scrub the remaining stain with scouring powder or a strong soap solution.

If the stain is old, cover it with flannel soaked in a solution of equal parts acetone and amyl acetate. Cover the flannel with a pane of glass or a thin concrete slab for 10 to 15 min. Repeat if necessary.

Rinse when the cleaning process is complete.

Grease: Scrape the grease from the surface. Scrub with scouring powder, strong soap or detergent, or sodium orthophosphate. If the stain persists, make a stiff poultice with one of the chlorinated solvents. Repeat if necessary. Rinse.

Dirt: Most dirt can be removed with plain water or with a soft brush and water containing a mild soap. If a stronger solution is necessary, use 19 parts water to 1 part hydrochloric acid. If the dirt contains a lot of oil, use the methods for removing lubricating oil. Also, hot water pressure cleaning is generally effective for removing dirt.

If the dirt is clay, scrape off all that has hardened. Scrub the stain with hot water containing sodium orthophosphate.

Mildew: Mix 1 oz each (by weight) powdered detergent and sodium orthophosphate, 1 qt commercial sodium hypochlorite solution, and 3 qt water. After applying the mixture, wait a few days and then scrub the area. Rinse with clear water. Caution: sodium hypochlorite solution bleaches colored clothing and may corrode metal.

Graffiti: Apply a proprietary cleaner that contains an alkali, a solvent, and detergent. After scrubbing the graffiti with a brush, leave the cleaner in place for the time indicated by the manufacturer. Rinse thoroughly. Avoid contact with skin.

Chewing gum: High pressure hot water removal is usually the most cost effective. You can also chill the gum with ice or commercial aerosol freezing agents. Chip and scrape off as much as possible. Apply carbon disulfide, chloroform, or denatured alcohol alone or in a poultice. Gum is known for leaving a shadow, this will fade over time and from subsequent cleanings.

SAFETY WITH CHEMICALS

When using chemicals, the contractor should wear gloves, face shields or masks. Have soap, water, and towels available for prompt washing and rinsing in case of emergency. Do not save unused portions of stain-removal solutions; discard safely.

Concrete cleaning can enhance the appearance ofyour property as well as protecting you from mold, mildew and other allergens.

Harrisburg, Carlisle, Hershey, Camp Hill, Mechanicsburg, Middletown