Basics of Surface Preparation

Lindy A.'s picture
Lindy Ausburne


There are “no cut and dry answers,” only a combination of potential solutions. The best methods to clean, strip, or otherwise prepare a concrete surface … prior to adorning it with a creative form of decorative concrete … is not a “cut and dry” question that is easy to answer.

Some facets of surface preparation are obvious … while others will depend on the type of foreign matter that must be removed, safety precautions that require consideration such as areas which do not have adequate ventilation, need to protect adjoining walls or fixtures and landscaping, mandated environmental constraints and concerns related to solvent content of some strippers; along with the use of specialty cleaning and surface preparation equipment which requires a certain degree of knowledge as to the proper use of them in order to achieve desired profile without harm to the substrate itself.


Having specialized in the concrete resurfacing industry for over 25 years there are certain stripping methods I used in the past, as pertaining to hazardous chemicals, that I no longer consider viable in today’s more environmentally safe and health conscious world; therefore, “the hunt is always on for more user friendly and green safe alternatives.” Example: Fire ants are a menace to people, livestock, and other creatures great and small.


There are various poisons and chemicals that can be used to kill them. Thinking “outside the box” one environmentally friendly solution would be to import anteaters. They could be turned loose in pastures or regions of the country which are plagued by fire ants. Anteaters are docile creatures, not harmful to humans or other animals, and do not emit any type of toxic waste that must be properly disposed of. Of course I realize that my solution lacks acceptability by the general public, governmental agencies, and a majority of those who I have suggested it to over the years, but it is a prime example of “thinking outside the box.”


The following article contains “tried and true” methods as related to cleaners, strippers, and specialty surface preparation equipment; however, the content should not be construed as being the only acceptable ways and means to do so, result being a virgin clean concrete, over which to apply your artistic concrete concepts. BASICS All concrete surfaces to be treated, stained, overlaid, or otherwise adorned must be structurally and mechanically sound, clean, not have an excess of rising moisture/vapors, and dry.


Concrete must be free of laitance, efflorescence, oils, waxes, curing compounds, grease, old coatings or sealers, and any other impediments to reactions or adhesions. There are various types of chemical strippers available for the removal of previous adhesives/mastics, coatings, and sealers; a wide realm of oil/grease/contaminate removers; and mechanical equipment such as floor maintainers, grinder/sanders, scarifiers, shot-blasters, dry sandblasting, and hydroblasting with water/turbo tip or sand/water injector assembly … any combination of which will provide you with a clean substrate, assuring a successful outcome.


REMOVAL OF STAINS FROM CONCRETE This is an excellent article in the Canadian Building Digest (published by: National Research Council Canada) titled “Removal of Stains from Concrete Surfaces” which discusses (provides detailed information) on the effective removal of various forms of stains on concrete … ranging from oil, blood, ink (fresh, old, India), beverages, asphalt and emulsified bitumen, tar and tobacco, various corrosives (rust, bronze, copper), fire, smoke and wood tar, and those related to growth of microorganisms (algae, fungus, mold). To access this article go to: (click on “English,” then “Publications,” scan down to “Canadian Building Digest,” then go to article number #153).


Note: there are hundreds of trade related articles pertaining to our industry in the “Canadian Building Digest.” GLUE & MASTIC REMOVAL TECHNIQUES White and yellow linoleum glue are typically water based. Recommend, prior to using a chemical stripper, that you first try using very “hot” water. Let the water stand for approximately 10 minutes to soften up the glue. After doing so, use a floor scrubber with a black pad to remove a majority of the hot water emulsified glue. Clean remaining residue by scrubbing with a biodegradable detergent and hot water, mopping and rinsing thoroughly. A wet/dry vac works well on indoor projects for removal of rinse water.


Black glue can sometimes be removed with mineral spirits (exercise extreme caution, extinguish all flames, and have plenty of ventilation). Let the mineral spirits soak for about 5 minutes, then scrape the floor. Keep in mind that you must work in small sections of no more than 100 sq.ft. After you have scraped off all that is possible, follow up with a floor scrubber with black pad. Note: it might be necessary to use a floor sander with 60 grit sanding screen. Clean and scrub using biodegradable detergent and hot water, mop and/or vac, and rinse thoroughly. Reference to a floor scrubber with black pad is the most efficient removal method; however, manual labor using a nylon bristled push broom will suffice. If the floor has VCT or adhesive floor tiles they can generally be removed by first flooding the surface with very hot water which will loosen their bond and make removal easier. If the tiles are of a different composite there is mechanical scraping equipment in which the blade will go between the flooring and the concrete substrate, pealing the flooring up.

After removal, glue residues can be removed by one of the below strippers or cleaning agents, or possibly one of the methods covered above. “INSIDE THE BOX” … CHEMICAL STRIPPERS The question as to the removal of sealers, glues, mastics, paints, and thin mil coating, and contaminate stains/discolorations is a frequent question on the decorative concrete forum. Listed below are several strippers and cleaners which perform admirably; however, keep in mind that circumstances and conditions will vary on each jobsite (i.e.: results as to their use cannot be guaranteed). Bare Bones, Sunnyside, Klean Strip III (KS-3), RemoveAll Citra-Peel, Hot Strip, and Glu-Gone by EZ Chemicals USA Matic Remover by Essco, Hydrostrip (#500, 502, 503), Goo-Gone Heavy Duty Floor Stripper and Big Orange by Zep Premium Paint and Epoxy Remover by Jasco Floors that have had VCT or other types of adhesive tile frequently will have permanent stains reflecting their placement which you may not be able to completely remove with strippers or specialty cleaners.

Of course these images are not a concern if a decorative concrete overlayment is to be applied; however, if the surface is to be acid stained there will generally be a ghost image of tiles which can either be embraced using stains that will camouflage them to some degree, or if a 100% resolution is required alternative would be the application of a micro-topping or overlayment which would provide ultimate acid staining results. “OUTSIDE THE BOX” …


ENVIROMENTALLY SAFE ALTERNATIVE STRIPPERS: There are several new lines of “green safe” strippers which are soybean based, developed to remove glues and mastics, as well as coatings and sealers. Their strippers are non-toxic, 100% biodegradable, non-corrosive, and they have no offensive odors or fumes. Available through many distributors nationwide. COMMON SENSE CAN SAVE LIVES Prior to the onset of any project, first read and heed all the recommendations and safety precautions of the manufacturer (label or technical data sheets will provide you with specifics). Many strippers contain hazardous, toxic, contaminative, flammable liquids.


Safety precautions associated with solvent based materials will require the use of respirators having proper filter, fresh air ventilation, extinguishing of all pilot lights in area as well as not using any type of equipment that has the potential to spark, and the sealing off of central air conditioning/heating vents which could carry the fumes into ductwork and other rooms in the building.


The hazards of using solvent based strippers in below grade basements is even more of a safety concern since it is more difficult to properly ventilate below grade areas and the fumes tend to hang in the air for a prolonged period of time. Helpful hint …remove offensive fumes or odors use 1 disposable baking tray (13”x 9”x1”) for each 100 sq.ft. of floor space in a room. Fill the baking tray with dry coffee granules out of the can. The dry coffee will absorb the odors in the air, just as baking soda does in your refrigerator. I have used this method to absorb the worst of odors such as those associated with fiberglass resins and gel coats w/MEKP catalysts, aliphatic urethanes, solvent based sealers and strippers, etc. with great success. When the odor is gone, simply dispose of the coffee.


EQUIPMENT that goes HAND-IN-HAND with STRIPPERS: After you have scraped as much residue as possible off the substrate, follow up using a floor maintainer with a black pad (alternative, floor sander with 60 grit). Depending on the foreign matter you are removing, the scattering of a uniform grade of very fine sand over the area when using the floor maintainer can be an acceptable technique; however, it is of the utmost importance that you exercise great care not to scratch or mar the floor if your intention is to acid stain the surface upon completion. Scrub the floor with a biodegradable detergent (can use a blue or white pad on the floor maintainer), rinse thoroughly, mop, wet/dry vac, allow to dry. For those that specialize in large commercial surfacing an auto-scrubber is worth the investment. Floor grinders, scarifiers, and planers offer another mechanical means of floor preparation, but you must keep in mind that improper use of them can lead to uneven surfaces, less consistent profile, circular scar like scratches, and other visible damage the substrate.


Floor grinders will effectively remove various glues/mastics, paints/coatings, previous sealers, and other foreign matter, as a well have the potential to provide an acceptable profiles for maximum bonding of overlayments; however, they should never be used by novices who may inadvertently vandalize their own floor. Furthermore, while some of this type of equipment offer dust collection devices, many others tend to fill the air with dust … of course their easier to maneuver around machinery, permanent fixtures, and do not require special types of power accessibility.


I recommend that you carefully consider alternatives to these types of equipment if your intention is acid stain the surface. Shot-blast equipment is the ultimate means to obtain a virgin clean slab with an acceptable profile if a modified cementitious overlayment is to be applied. Steel shot is hurled at substrate using the appropriate size of shot. This process removes previous coatings, laitance, sealers, glue/mastic, weak concrete, and contaminates that may have penetrated the top mils of the concrete.


As a self contained unit, they clean the surface, effectively remove contaminates, and collect the dust from the concrete in a separate dust collector. Shot blasting eliminates the need for strippers, water, detergent, chemicals, etc. Results are rapid, within 1/6” of a wall or fixture. Do not recommend shot blasting if the surface is to be acid stained since there will be some degree of ghost image lap marks. Shot blasting should be sub-contracted out to professionals that offer this service unless a contractor has had “first hand” knowledge and experience. Sand blasting will remove foreign matter, sealers, and coatings; however, doing so creates a great deal of dust, sand bounce back, and a general mess. Hydroblasting with a pressure washer, having 2400-3500 psi, works well for removal of thin mil exterior coatings (note: using higher degrees of pressure, such as 5,000 psi, will actually start to remove the top layer of concrete; therefore, is not recommended). This process is accelerated by the use of either a turbo/rotating tip or using a sand injector accessory. The turbo tip concentrates the pressure in smaller areas; while the sand injector siphons up fine sand through a hose, mixing it with water as it exits the gun for more rapid results without the dust that is associated with ordinary sand blasting. Hydroblasting and hydro-water/sand-blasting both are environmentally friendly ways to remove foreign matter, as well as thin mil coating or sealers, without toxic chemicals or harm to the sound substrate.


Scabblers are pneumatic machines that pound the substrate to remove high build overlayment materials (be they cementitious in nature, multi-build epoxy/quartz ones, ¼” flooring tile, old epoxy/stone systems, etc. Great care should be exercised if this type of equipment is to be used in order to prevent damage to the original concrete substrate.


SURFACE DEFECTS Surface defects, not associated with normal cleaning and substrate preparation (cracks, holes, chips, spalls, non-structurally sound, those having levelness issues, etc.) must be properly addressed and remedied, with prior to proceeding with application of decorative concrete surfaces in accordance with ICRI standards.


SUCCESS NEED NOT BE PUZZLING Whether your plans are to acid stain, place an architectural concrete overlayment, or otherwise adorn a drab concrete slab, unless you properly prepare your concrete substrate first, the premium quality of the materials you use over it will not guarantee a successful outcome. The “highest and best use of your decorative concrete talents and time” are applying your trade on a surface that is free of all contaminates and previous coatings that may impede your ability to do so; therefore, you might want to consider sub-contracting your surface preparation work out to professionals that specialize in doing so, especially if it is a large commercial project. If you take this route, do so in writing … state specifically what they are to do; furthermore, make it clear that if the surface prep sub-contractor damages the floor they will be liable for all costs incurred in remedying the situation to your satisfaction.


Much of the information contained in this article may seem elementary to those that have specialized in the decorative concrete industry for years, but I feel it is better to cover all bases than leave any unattended. There is no real secret to success …it is merely a matter of the concrete being structurally sound, proper surface preparation, the use premium materials having a proven performance history, and your creative craftsmanship. May all your decorative concrete endeavors lead you down the pathway to prosperity and recognition for a job well done!


Lindy Ausburne


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This is totally helpful.

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I always like your blog post because you always comes with different ideas and information. The contents has provided useful information on prepration of surface. I found it helpful for all constrction releted people. Thanks.

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