There are many types of concrete surfaces and just as many ways to get those surfaces clean, or restored as close enough to their original appearance as possible.
One of the toughest cleaning and maintenance and, if necessary, restoration, problems comes about when concrete is attacked by oil, grease and antifreeze from vehicles.
The ugly-looking deposits often accumulate to the point that normal maintenance can’t get the surface clean.
Here are some thoughts on tackling that tough task, as well as other cleaning chores and processes that involve different concrete surfaces.
Bare or worn concrete floors: sweeping or vacuuming is most effective, followed by spot, damp mopping where visibly soiled.
Oil spots can be removed or lightened by spot treating them with a good degreaser or oil emulsifier.
For large areas, use an autoscrubber.
Sealed floors: Sweep, vacuum and spot, wet or flood mop or auto scrub with a variety of cleaning solutions depending on soil conditions.
Use a neutral floor detergent for daily care in most locations.
Avoid the use of harsh chemicals such as a strong acid or alkaline cleaner on bare or damage concrete floors.
If a high alkaline or acid cleaner is needed due to soil condition, after cleaning, neutralize the surface with the opposite pH to return the floor to a pH of 7 (neutral), then rinse well with clear water and pick up with an auto scrubber or wet vacuum.
Decorative concrete: Use a neutral cleaner and a deck brush for daily cleaning.
For heavy cleaning or large areas, use a floor machine and nylon brush, non-abrasive pad (white, red) or a low-pressure washer (under 1,500 psi) and pick up spent solution with a wet vacuum.
When the surface becomes dull or scratched, reapply one or two coats of an acrylic finish to restore the shine.
Scrub with a neutral detergent. Do not use acid-based high alkaline products for regular daily maintenance.
Sealer and finish
Apply one or two coats of a penetrating sealer to new or restored concrete floor surfaces.
Topical coatings such as a urethane, acrylic or a polymer finish or sealer, paint or epoxy may also be applied to properly prepare concrete floors.
Special coatings are available for use out of doors where harsh weather, moisture and ultraviolet rays may be present.
When renewable sacrificial topical coatings such as low-solid content acrylic or polymer finishes are used, an ongoing preventive maintenance program (scrub, burnish, strip, recoat) must be established to maintain the desired shine and appearance level.
Scrub with a neutral detergent, degreaser, stripper, then acid etch the floor, then neutralize and rinse well.
Allow to completely dry for 48 to 72 hours and then apply one or more coats of concrete sealer, finish, paint or other coating per manufacturer’s directions.
When applying non-breathing coating or covering, test for dryness with a moisture meter before application.
Grind, scarify, bead or shot-blast the surface prior to applying finish, coating or over coating, or installing a floor covering.
If this fails or cannot be used, the slab may need to be resurfaced, replaced or accepted as is.
Spot and stain removal
Scrape excess material from the surface with a putty knife and wire brush.
Scrub the area with a degreaser and/or powdered cleanser and a coarse nylon-grit brush or dark synthetic pad.
An absorbent poultice may also be used in an attempt to remove spots and stains.
Scabbling; scarifying; grinding; pressure washing; sand, soda, or dry ice blasting; water jetting; steam or vapor cleaning may be used to clean, as well as remove stains, adhesives, paint and other materials.
As with all cleaning processes, to avoid damage to the surface, test all procedures and products in a small inconspicuous location (6-square-inch area) prior to widespread use.
Allow the surface to dry for at least 72 hours before evaluation to see the final result of any cleaning process.
Some processes may change the color, appearance and texture of the surface, so proceed with care, caution and at your own risk.
It is best to discuss the possibility of damage or change with your customer or supervisor to get his or her input and approval before proceeding.
An excellent booklet titled: “Removing Stains and Cleaning Concrete Surfaces” is available from the Portland Cement Association by calling (847) 966-6200, emailing firstname.lastname@example.org, or logging on to www.cement.org.
Other cleaning techniques
Dry absorbent spot removal process: Apply a dry absorbent mix consisting of 75 percent diatomaceous earth (filter powder) and 25 percent cement.
Brush it in to the surface and allow to dwell for one to two hours and remove with a broom, then vacuum the surface.
Chemical cleaning: This can range from normal scrubbing or stripping with mild detergent solutions and enzyme-based products to the use of hazardous materials such as specialized solvents, acids and alkalis.
Follow all manufacturer’s instructions closely to avoid damage, injuries and issues with indoor air quality, worker safety, and proper disposal of slurry and empty containers.
Mechanical cleaning: Concrete can be cleaned by power equipment that loosens and removes a layer of the concrete surface itself.
A number of heavy-duty machines of different types and sizes are available, like scabblers, scarifiers, scalers, shot or bead blasters, cutters, profilers, grinders, groovers, planers and scourers.
These machines abrade the surface in one or more of the following ways: Carbide-tipped cutter bits, grinding stones, saw blades, hardened steel cutting wheels or shot, tungsten-tipped carbide bits or steel-wire brushes.
The process is often noisy and dusty, although newer equipment incorporates an effective vacuum system to capture most of the dust and debris during the process.
Flame cleaning: If problems persist, flame cleaning of the surface may be needed.
Propane torching requires special equipment that draws oils and other impurities to the surface and incinerates them.
When using this equipment, take all the precautions necessary when working with open flames, including having a fire extinguisher nearby.
After propane torching the area, spot cleaning of the surface with chemical means will be needed to remove remaining residue.
Common repairs that occasionally may be needed include: Powdering or dusting of the surface, random cracks, spalling, holes, joint damage, sunken concrete, frost heave, pop outs, corner breaks, rocking slabs and edge curl.
When repair attempts fail and there is no other acceptable option, an entire slab or portion thereof may have to be removed and replaced.
Depending on available staff, technical skill and access to equipment and chemicals, many of the specialized tasks discussed above may be best accomplished by using the services of an independent specialty contractor.