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Water and Wastewater Protective Coating Systems | Article 11 of 24

Concrete Surface Preparation, Profile, Cleanliness, and Acceptance

Surface preparation must produce clean, sound, open, and properly profiled concrete capable of supporting the specified coating or lining throughout its intended service life.

Surface Preparation Controls Lining Performance

The lining manufacturer supplies the protective material, but the contractor creates the surface to which that material must bond. Concrete that is dirty, weak, excessively smooth, contaminated, damp beyond the product’s limits, or covered with laitance cannot provide dependable support.

Surface preparation is not judged only by how rough the concrete looks. Acceptance should consider cleanliness, soundness, profile, dryness or moisture condition, repaired defects, environmental conditions, and compatibility with the complete coating system.

Begin with Approved Requirements

Before equipment is selected, identify the required condition of the completed surface. The project specification and coating manufacturer should define the governing standard, preparation method, required concrete surface profile, moisture limits, minimum substrate strength, repair requirements, and acceptance tests.

The preparation plan should establish:

• The concrete areas included in the work
• The required degree of cleanliness and soundness
• The specified ICRI Concrete Surface Profile, commonly called CSP
• Acceptable preparation methods and prohibited methods
• Dust collection, containment, ventilation, and waste-disposal requirements
• Treatment of cracks, joints, penetrations, edges, and repaired areas
• Required testing and frequency
• The inspection hold point before primer or lining application

Cleaning, Repair, and Surface Preparation Are Separate Operations

Cleaning removes sludge, oil, grease, chemicals, biological material, and process residue. Repair replaces missing or deteriorated concrete and restores the required geometry. Surface preparation then removes laitance, weak surface paste, curing compounds, sealers, incompatible coatings, and other bond-inhibiting material while creating the specified profile.

One operation may contribute to another, but the contractor should not assume that pressure washing has created an acceptable profile or that abrasive blasting has removed oil embedded in the concrete.

What Must Be Removed?

Unless the approved system permits otherwise, the prepared concrete should be free from materials that can prevent penetration, wetting, or adhesion, including:

• Laitance and weak cement paste
• Dust, dirt, sediment, and loose aggregate
• Oil, grease, fats, and lubricants
• Biofilm, algae, microbial growth, and organic residue
• Efflorescence and soluble salts
• Curing compounds, sealers, form-release agents, and hardeners
• Unsound concrete and deteriorated repair material
• Existing coatings not approved to remain
• Chemical residue from cleaning or treatment processes
• Any other material identified by the specification or coating manufacturer

Understanding Concrete Surface Profile

Surface profile describes the texture and amplitude produced by preparation. Profile provides additional surface area and helps a coating or lining establish mechanical attachment to the concrete. The required profile generally becomes more aggressive as the thickness and physical demands of the protective system increase.

ICRI Guideline No. 310.2R provides molded Concrete Surface Profile comparator chips identified as CSP 1 through CSP 10. The chips provide visual and tactile reference surfaces ranging from very light preparation to aggressive profiles used for heavy overlays and repairs.

A CSP designation is a profile reference, not a complete preparation specification. Two surfaces can resemble the same CSP chip while differing greatly in cleanliness, soundness, moisture, and contamination.

More Aggressive Is Not Automatically Better

An excessively aggressive profile can expose coarse aggregate, create deep valleys, damage sound concrete, increase material consumption, trap air, and make holiday-free lining application more difficult. A profile that is too light may leave laitance, smooth paste, or insufficient texture for dependable adhesion.

Produce the profile required for the specified system. Do not substitute personal preference for the written requirements of the project and coating manufacturer.

Preparation Methods

Abrasive Blasting

Dry or wet abrasive blasting can remove laitance, weak surface material, existing coatings, and contamination while creating an open profile. Abrasive type, size, hardness, pressure, nozzle distance, and operator technique affect the result. Dust and spent abrasive must be completely removed.

Shot Blasting

Vacuum-assisted shot blasting is effective on accessible horizontal surfaces. Travel speed, wheel speed, shot size, and machine condition determine the profile. Overlapping passes, turning marks, and untreated edges require attention.

Grinding

Diamond grinding can remove coatings, high spots, laitance, and surface contamination. Incorrect tooling or excessive polishing can leave the concrete too smooth. Grinding marks and inaccessible low areas must be inspected carefully.

Scarifying, Scabbling, and Milling

These impact or cutting methods can remove thicker materials and create aggressive profiles. They may also bruise, fracture, or microcrack the remaining surface when improperly selected or operated. Follow-up preparation may be necessary.

High-Pressure and Ultra-High-Pressure Water

Waterjetting can remove coatings, contamination, and deteriorated concrete without introducing abrasive. The contractor must control runoff and confirm that the resulting moisture condition, cleanliness, and profile are acceptable before coating.

Hand and Small Power Tools

Hand tools, needle scalers, small grinders, and similar equipment are useful at corners, penetrations, transitions, equipment bases, and other restricted areas. They should supplement the primary preparation method without leaving visibly different or inadequately prepared zones.

Acid Etching Has Important Limitations

Acid etching is not a universal substitute for mechanical preparation. It may react unevenly with dense, contaminated, previously coated, or chemically altered concrete. Acid and reaction products must be completely removed, and the concrete must be neutralized, rinsed, dried, and verified as required.

Do not use acid etching unless the specification and coating manufacturer permit it and the contractor can control chemical exposure, runoff, neutralization, residue removal, and the final surface condition.

Prepare a Representative Test Area

A test area establishes whether the selected equipment, abrasive, tooling, pressure, travel speed, and operator technique can achieve the required surface. It should be placed on representative concrete and include repairs, vertical areas, corners, or other conditions when practical.

Once accepted, the test area becomes a field reference for production work. Document the method, equipment settings, appearance, profile, cleaning procedure, and parties who accepted it.

Edges, Corners, and Difficult Areas

Large equipment cannot reach every part of a water or wastewater structure. Corners, wall-to-floor transitions, pipe penetrations, equipment bases, anchor pockets, channels, stairs, sumps, drains, and areas behind obstructions must receive equivalent preparation.

These locations are also common sites for pinholes, thin film, holidays, and early failure. Include them in the preparation plan rather than treating them as incidental touch-up work.

Preparation Exposes Previously Hidden Defects

Mechanical preparation may reveal cracks, bugholes, voids, honeycombing, corroded reinforcement, weak repairs, chemical attack, and deeper deterioration that were not visible during the initial survey.

Stop at the established notification point, mark the defects, photograph them, and obtain direction. Do not conceal changed conditions with primer, resurfacer, or additional coating material.

Remove Dust and Preparation Debris

Dust can settle into pores and profile valleys where it is difficult to see. Applying primer over dust bonds the coating to the dust rather than to the concrete.

Final cleaning may include:

• Industrial vacuuming with suitable filtration
• Clean, dry, oil-free compressed air when permitted
• Brushing followed by vacuuming in corners and depressions
• Rinsing when approved and followed by adequate drying
• Inspection of horizontal surfaces after airborne dust has settled

Compressed air should be checked for oil and moisture contamination before it is directed onto a prepared surface.

Protect the Prepared Surface

Prepared concrete can quickly become contaminated by foot traffic, leaking equipment, condensation, process water, rain, dust, oil, insects, or work performed by other trades.

• Restrict access after final preparation.
• Use clean footwear or protective covers where appropriate.
• Prevent hoses and equipment from dragging contamination across the surface.
• Maintain ventilation without introducing dust or exhaust.
• Monitor for condensation and water intrusion.
• Reinspect and reprep contaminated or weathered areas before coating.

Surface Acceptance

Acceptance should occur after preparation and final cleaning, but before primer or lining application. The inspection should cover the entire work area, not only easily accessible locations.

Acceptance may include verification of:

• Specified surface profile using the approved ICRI comparator chips
• Removal of laitance, coatings, curing compounds, sealers, and contamination
• Soundness of the remaining concrete and completed repairs
• Absence of dust, loose material, and spent abrasive
• Treatment of cracks, voids, bugholes, joints, penetrations, and transitions
• Required moisture condition and environmental readings
• Pull-off strength or other tests required by the specification
• Written release of the area for coating application

Pull-Off Testing and Failure Location

Pull-off testing can be used to evaluate the tensile performance of a prepared concrete surface, repair material, or applied coating system. The reported value alone does not tell the complete story.

Record where the test assembly failed: within the concrete, within a repair material, at an interface, within the coating, in the adhesive used to attach the test fixture, or through a combination of locations. The failure mode helps determine what part of the system controlled the result.

Contractor’s Field Checklist

• Is the required preparation standard identified?
• Is the required CSP or other profile criterion documented?
• Has a representative test area been prepared and accepted?
• Have all contamination and weak surface materials been removed?
• Are repaired areas and original concrete prepared consistently?
• Have corners, penetrations, transitions, and restricted areas been prepared?
• Have newly exposed defects been documented and corrected?
• Has all dust and debris been removed?
• Is the moisture condition acceptable for the specified system?
• Has the surface been formally accepted and released for coating?

Knowledge Check

1. Does matching an ICRI CSP chip prove that the concrete is ready for coating?

No. The CSP comparison addresses surface texture. The concrete must also meet the project requirements for cleanliness, soundness, moisture condition, repair, contamination, and environmental conditions.

2. Why is an excessively aggressive profile undesirable?

It can damage sound concrete, expose excessive aggregate, increase material consumption, trap air, create pinholes, and make continuous lining coverage more difficult.

3. Why should the failure location be recorded during pull-off testing?

The failure location identifies the weakest plane in the tested assembly and helps distinguish substrate failure, interface failure, coating failure, and test-adhesive failure.

Technical References and Further Study

• AMPP SSPC-SP 13/NACE No. 6-2024, Surface Preparation of Concrete. This active standard addresses mechanical and chemical preparation of concrete before application of bonded protective coating and lining systems.
• ICRI Guideline No. 310.2R-2013, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair. This guideline describes preparation methods and includes the CSP 1 through CSP 10 comparator system.
• ASTM D4258-23, Standard Practice for Surface Cleaning Concrete for Coating.
• ASTM D4259-24, Standard Practice for Preparation of Concrete by Abrasion Prior to Coating Application. This practice addresses producing a concrete profile and removing foreign material and weak surface laitance.
• ASTM D7234-22, Standard Test Method for Pull-Off Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
• The coating manufacturer’s current technical data sheets, safety data sheets, concrete-preparation requirements, moisture limits, primer instructions, and written project recommendations.

Standards and manufacturer requirements may be revised. Confirm the current edition and the exact project requirements before preparing or accepting the concrete surface.

Professional responsibility: This article provides foundational education and does not replace the project specification, approved repair documents, manufacturer instructions, site-specific safety plan, or judgment of the responsible design professional. When the prepared surface differs from the specified condition, stop and obtain written direction before applying the coating or lining.

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