Secondary Containment Coating Systems for Industrial Contractors

Article 07 of 24

Oil, Chemical, and Embedded Contamination in Concrete

Contamination does not always remain on the surface. Oil, fuel, chemicals, cleaners, salts, and process materials can penetrate concrete and later interfere with adhesion, cure, and lining performance.

Learning Objectives

After completing this article, you should be able to:

• Explain how contaminants enter and remain in concrete
• Recognize visual and historical signs of contamination
• Distinguish surface cleaning from removal of contaminated concrete
• Plan a cleaning and verification sequence
• Use test areas and adhesion testing appropriately
• Recognize when further removal or written direction is required

Concrete Can Look Clean and Still Be Contaminated

Concrete contains pores, capillaries, cracks, and voids. Liquids can migrate below the visible surface and remain after ordinary cleaning. Grinding or blasting may initially expose apparently clean concrete, but deeper contamination can move back toward the surface.

Applying a high-performance lining over contaminated concrete does not isolate the problem safely. The contaminant may interfere with wetting, penetration, cure, or bond and cause blistering or delamination after the work has been accepted.

Common Sources of Contamination

• Lubricating oil, hydraulic fluid, grease, and cutting fluids
• Gasoline, diesel fuel, aviation fuel, and process oils
• Acids, alkalis, solvents, salts, and process chemicals
• Detergents, surfactants, disinfectants, and cleaning residues
• Curing compounds, sealers, densifiers, and form-release agents
• Silicone, wax, polish, and maintenance treatments
• Salts carried by groundwater, wash water, or previous chemical exposure
• Residue from removed coatings, mastics, adhesives, or membranes
• Concrete repair products incompatible with the proposed system
• Unidentified materials absorbed during years of facility operation

Begin With the Facility’s History

The appearance of the surface is only part of the investigation. Ask operators and maintenance personnel how the area has been used.

Important questions include:

1. What materials have been stored, transferred, or processed here?
2. Where have spills or leaks occurred?
3. How long did released materials remain before cleanup?
4. What cleaning chemicals and methods were used?
5. Was the concrete previously sealed, coated, or treated?
6. Where have previous coatings failed?
7. Have contaminated areas been patched or covered?
8. Do liquids regularly collect in low areas or around equipment?
9. Are drains, trenches, cracks, and joints known leakage paths?
10. Has the facility’s chemical service changed over time?

Visual Warning Signs

• Darkened, discolored, or unusually smooth concrete
• Areas that remain wet-looking after surrounding concrete dries
• Visible oil, grease, wax, or chemical residue
• Strong or unusual odor after surface removal
• Water that beads instead of wetting the surface uniformly
• Powdery deposits, crystallization, or efflorescence
• Soft, weakened, eroded, or chemically attacked concrete
• Blisters or delamination in an existing coating
• Repeated failure in the same location
• Contamination emerging from cracks, joints, or pores after preparation

Absence of visible staining does not prove the concrete is uncontaminated. Conversely, discoloration alone does not identify the contaminant or its depth.

Surface Contamination Versus Embedded Contamination

Cleaning Must Come Before Profiling

Heavy oil, grease, and chemical residue should generally be removed before aggressive mechanical preparation. Blasting or grinding through visible contamination can spread it over a larger area, embed it in newly exposed concrete, contaminate equipment, and create contaminated debris.

A planned sequence may include:

1. Identify the contaminant and associated hazards
2. Stop active leaks and isolate the source
3. Remove bulk material using approved recovery methods
4. Apply the approved cleaner at the correct concentration
5. Provide the required dwell time and agitation
6. Recover contaminated liquid instead of spreading it
7. Rinse or neutralize as required by the procedure
8. Allow the concrete to dry sufficiently for evaluation
9. Mechanically remove contaminated or unsound concrete
10. Reinspect and verify the prepared surface

Solvent Wiping Is Not a Cure for Oil-Soaked Concrete

An uncontrolled solvent wash may dissolve oil and transport it farther into the concrete or across the surface. It can also create fire, exposure, ventilation, waste, and compatibility hazards.

Use only an approved cleaning procedure that identifies the cleaner, application method, containment, recovery, rinsing, disposal, drying, and verification requirements. Do not improvise with available solvents.

Mechanical Preparation Does Not Guarantee Decontamination

Shotblasting, abrasive blasting, grinding, scarifying, and other mechanical methods can remove contaminated surface material. Their effectiveness depends on the contaminant’s depth and the amount of concrete removed.

When contamination extends below the prepared surface, additional removal may be required. The process may need to alternate between cleaning, removal, drying, and reevaluation.

Do not accept a surface solely because it has the specified profile. Profile, cleanliness, soundness, dryness, and freedom from bond-breaking contamination are separate acceptance requirements.

Chemical Damage May Require Concrete Removal

Some chemicals do more than contaminate concrete. They react with and weaken the cement paste. A coating bonded to chemically weakened concrete may separate with a layer of concrete attached to its backside.

Warning conditions include:

• Soft or friable concrete
• Surface erosion or loss of paste
• Loose aggregate
• Unusual powdering after preparation
• Low pull-off strength with failure in the concrete
• Continuing chemical odor or residue after surface removal
• Deterioration extending around cracks, joints, or drains

Remove unsound material to the extent required by the approved repair procedure. Structural or extensive deterioration requires evaluation by the responsible design professional.

Verification Is More Than a Visual Check

Visual inspection is necessary but may not establish whether embedded contamination remains. Verification should be agreed upon before cleaning begins.

Depending on the project, verification may include:

• Visual examination under adequate lighting
• Comparison with uncontaminated concrete
• Uniform wetting observations under an approved procedure
• Surface pH or residue testing when specified
• Soluble-salt testing when required
• Laboratory evaluation of samples
• Manufacturer-approved test patches
• Pull-off testing with documentation of the failure plane

The project must define how the results will be interpreted. A test without an agreed acceptance criterion cannot independently determine whether the surface is acceptable.

Use Representative Test Areas

Before committing the entire project to a cleaning and preparation procedure, perform representative test areas in locations approved by the responsible parties.

A useful test area should confirm:

• Whether the proposed method removes visible residue
• How much concrete must be removed
• Whether contamination returns after drying
• Whether the required surface profile can be achieved
• Whether the prepared concrete is sound
• Whether the primer wets and bonds properly
• Whether pinholing, outgassing, or other defects occur
• Whether the procedure can be safely and practically repeated

Test areas should represent both typical and severe contamination. Success in a lightly affected location does not validate the procedure for heavily contaminated concrete.

Pull-Off Testing and the Failure Plane

A pull-off value should not be considered without examining where the test assembly failed. Failure may occur:

• Within the concrete
• At the concrete-primer interface
• Within the coating or lining system
• At the adhesive used to attach the test fixture
• Through a combination of several failure planes

A numerical result accompanied by contaminated concrete at the failure surface may tell a different story from the same number obtained through failure in sound concrete.

Test quantity, locations, cure time, equipment, scoring procedure, and acceptance criteria must be established before testing.

Cleaning Waste Must Be Controlled

Cleaning can produce contaminated water, sludge, abrasive, dust, concrete debris, used absorbents, and disposable protective equipment. The cleaning operation must not spread contamination outside the work area.

The work plan should address:

• Containment of cleaning liquids and debris
• Protection of drains and operating equipment
• Collection and labeling of waste
• Waste characterization by the responsible party
• Approved storage, transport, and disposal procedures
• Decontamination of tools and equipment
• Worker exposure controls and required protective equipment

Conditions Requiring Written Direction

• The contaminant has not been identified
• Cleaning spreads residue or produces uncontrolled waste
• Contamination returns after the surface dries
• Required removal depth exceeds the anticipated scope
• Concrete remains soft, weak, or chemically damaged
• Test areas do not meet the required acceptance criteria
• The proposed primer is not approved for the remaining condition
• Removal could affect reinforcement or structural capacity
• The cleaning and waste-disposal responsibility is undefined

Contamination-Control Records

• Identified or suspected contaminant
• Original location and visible extent
• Safety Data Sheets and hazard information
• Approved cleaning and removal procedure
• Cleaning materials, concentration, dwell time, and equipment
• Quantity or depth of concrete removed
• Waste collection and disposal records
• Test-area locations and results
• Verification tests and acceptance criteria
• Before, during, and after photographs
• Written acceptance or direction from the authorized party

Technical References

• ASTM International, ASTM D4258-23—Standard Practice for Surface Cleaning Concrete for Coating
• American Concrete Institute, ACI PRC-515.3-20—Guide for Assessment and Surface Preparation for Application of Protection Systems for Concrete
• Association for Materials Protection and Performance, Surface Preparation of Concrete
• International Concrete Repair Institute, ICRI Guideline No. 310.2R—Selecting and Specifying Concrete Surface Preparation
• Current system-manufacturer instructions for cleaning, contamination assessment, surface preparation, test areas, priming, and adhesion testing

Verify the current edition, scope, safety requirements, and project acceptance criteria before using any cleaning or testing procedure.

Key Takeaways

• Concrete can remain contaminated beneath an apparently clean surface
• Identify and remove bulk contamination before aggressive mechanical preparation
• Uncontrolled solvent wiping can spread or deepen contamination
• Profile alone does not prove cleanliness or soundness
• Chemically weakened concrete may require removal and repair
• Representative test areas should be completed before full production
• Document the procedure, verification, waste, and written acceptance

Professional responsibility: Do not apply a containment lining over unidentified or unacceptable contamination. When cleaning cannot produce sound, clean, verifiably acceptable concrete, stop and obtain written direction for additional removal, repair, testing, or system selection.

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