JPCL • July 2001 • PCE 33Copyright ©2001, Technology Publishing Company

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Cleaning Contaminated Concrete

Al FeuchtFeucht Resources, LLCMoorestown, New Jersey, USA: This question generates a series ofquestions that must be answered be-fore recommending both the coatingsystem and the surface preparation.The questions are as follows.• What is the degree of contamina-tion? The term “well contaminated” inthe question implies that there is a sig-nificant degree of contamination.• How old is the concrete?• Is the concrete slab on grade? If so,is there a vapour barrier under theslab? If no vapour barrier was used,what is the moisture transmission ratethrough the concrete floor?• Is there an existing coating or sealeron the floor?• How level does the floor need to befor its new use?• What level of aesthetics is desired?• What type of traffic will be present(e.g., foot, hand carts, lift trucks)?• What will be the cleaning proce-dures for the floor once it is installed?• Are there joints in the floor? If so,what are the dimensions?• Are there cracks in the floor? If so,how many, how wide, and where?

The answers to the above questionswill lead to the proper recommenda-tion for surface preparation and coat-ing. Usually, a parking garage has spe-cific areas of contamination that needto be cleaned before general surfacepreparation can be performed. TheSurface Preparation Standard SSPC-SP13/NACE No. 6, “Surface Preparationof Concrete,” is an excellent guide touse for both removing contaminationand preparing the concrete surface.This guide also provides reference in-formation on detecting and testing forcontamination.

The degree of cleanliness, surfacepreparation, and surface strength will

depend on the selected coating and itsintended use. For instance, manyepoxy primers tolerate some degree ofoil contamination. However, good gen-eral practice is to remove the greaseand oil contamination from at least thesurface of the concrete. Decontaminat-ed areas should then be tested to makesure they are not hydrophobic. That is,

if they can be wetted with water with-out beading, they have been deconta-minated adequately.

After the grease and oil are removed,surface preparation of the entire sur-face should be conducted. Rubber con-tamination and surface laitance shouldbe removed by mechanical means,such as centrifugal shot blasting. Thedegree of profile and removal of lai-tance depend on the type of coatingand the intended use of the floor.

The type of coating depends on theanswers to the above questions. Athin-film coating of 2 to 6 mils (50 to150 micrometres) will provide an im-proved appearance but will have limit-ed durability and will not hide surfaceimperfections. A high-build, broadcastor trowel-applied system of 125 to 250mils (3 to 6 mm) will hide surface im-perfections and will provide a highlevel of durability. In addition, manycoating systems that fall between the

6-mil and 125-mil (50-micrometre and3-millimetre) thickness ranges can beused, including high-build elastomer-ics. The durability and aesthetics ofeach system will vary.

The best approach is to have some-one knowledgeable in floor coatingsinspect the area and suggest a few op-tions.

Peter CurtisDumar ResinsLincolnshire, UK:The essence of longevity of any coat-ing system is, in the main, linked tocareful and correct preparation of thesubstrate, followed by the use of anappropriately specified product. Se-lecting the correct surface preparationtechniques, utilising the right equip-ment, and following the manufactur-er’s instructions carefully greatly in-crease the likelihood of a successfulapplication.

All too often, industrial floor con-tractors encounter heavy and in-grained contamination of a cementi-tious substrate by oil- andgrease-based components. Only spe-cialised surface preparation can re-move a build-up of grime from years ofuse. Initially, shot blasting will removethe surface contaminants, only to ex-

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QQ A building has been used as a car garage foryears, and the concrete floor has been well contaminated with oil, grease, antifreeze, etc.The building is being converted to a store andthe owner wants to paint the floor. Except for the contamination, the concrete is in excellentcondition. How should the floor be prepared andwhat coating should be used?

JPCL • July 2001 • PCE34 Copyright ©2001, Technology Publishing Company

pose the areas of more deeply ingrained oil and grease. Hotforced air equipment may then be used to deal with thisproblem.

Recycled shot blasting uses a wide variety of abrasives“fired” into the surface of the floor in a stream of com-pressed air. The air, grit, and surface particles are recycled,filtered, and reused where necessary. In the UK, chillediron grit and rounded shot particles are the abrasives mostcommonly used for this purpose. Different grades and sizesare used to vary the end profile of the floor. This workshould be carried out by a specialty surface preparationcompany. A trained operator can be expected to achieve upto 900 sq m (9,800 sq ft) of floor preparation in a typicalworking day using this method.

Hot forced air treatment directs an extremely hot gas jetflame onto the newly exposed cementitious surface. Thistreatment vapourises any oil-based contaminants in the up-per surface of the floor. Again, this is a specialised job, andonly skilled and trained operators should undertake it. Im-mediately after the heat treatment, a suitable floor sealantcoating should be applied. A high-solids, two-pack primeris recommended for this, using the residual heat in thefloor to bring about a faster cure. For more effective seal-ing, a second coat of the primer may be applied after the

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JPCL • July 2001 • PCE 35Copyright ©2001, Technology Publishing Company

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first coat has cured. It may be necessary to consult theresin manufacturer for advice on this point. Painting canfollow after the primer has hard-cured.

Once the floor surface has been effectively sealed, thetype of coating to use depends on what the floor area is tobe used for. Storage areas may be sufficiently protected bythe application of two coats of a water-thinnable two-packepoxy. If there is considerable vehicular traffic over the fin-ished surface, a high-build, solvent-free seal coat may be inorder. For chemical storage areas, a two-pack aliphatic ure-thane system may provide the answer.

Again, seek out the technical advice of a reputable floorresin manufacturer. Broad spectrum biocide additives areavailable in most coatings to provide additional protectionagainst mildew and fungal infestation in the finished floorsystem.

Mark MilewskiThe Valspar CorporationChicago, Illinois, USA:Ultimately, what will determine the adhesion of any coat-ing is the preparation of the substrate. Oil and grease aresome of the best bond breakers. I would recommend usinga highly alkaline detergent (with a pH of 12+). The deter-

gent should be scrubbed in and vacuumed out. This typeof extraction cleaning should be repeated until the greaseand oil stop leaching from the concrete during the de-greasing operation.

Once the substrate is free of the oily appearance, prepa-ration by mechanical means is recommended. Shot blast-ing is the preferred method for concrete preparation andwill ensure that any unsound, softened matter is removed.

After preparation, the surface should be inspected forfurther signs of leaching. Additional washing may be re-quired, followed by thorough drying. Apply an oil-tolerantprimer followed by the coating system specified.

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JPCL • July 2001 • PCE36 Copyright ©2001, Technology Publishing Company

• If my company employs an inspectionagency to verify compliance with spec-ifications for a painting project and thecoating subsequently fails premature-ly, should the inspection agency bearsome responsibility for the failure?

• What is the influence of admixtures(hardeners, dust suppressants, etc.) toconcrete on the subsequent adhesionof protective coating systems? If thereare negative effects, what can be doneto eliminate them?

• As a cost-cutting measure, some facilityowners have recently begun to providebidding contractors with the amount ofsteel to be cleaned and painted ratherthan provide facility design and detaildrawings. Is this a reasonable practice (tosolicit realistic bids)? Why or why not?

• How do you detect microbiologically-influenced corrosion?

• Are any of the laboratory electrochem-ical techniques used in coating re-search viable for the prediction of coat-ing performance in practice?

Responses should be 1–2 typed, double-spaced pages. Responses and questionsshould be sent along with your name, ad-dress, and telephone and fax numbers to: Brian Goldie, Publisher, PCEtel: +44 20-8288-0077; fax: +44 20-8288-0078; e-mail: brianpce@aol.com;or Karen Kapsanis, Editor, JPCLtel: +1 800 837 8303 (USA and Canada only) or +1 412-431-8300; fax: +1 412-431-5428; e-mail: kkapsanis@protectivecoatings.com.

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