The Membrane Is Only as Strong as the Surface Beneath It

A moisture-mitigation membrane can be chemically resistant, highly adhesive, and qualified for elevated concrete moisture. None of those properties will overcome a weak, contaminated, dusty, or improperly prepared substrate.

If the membrane is bonded to laitance, adhesive residue, curing compound, oil, weak concrete, or dust, the complete flooring or coating assembly depends on that weak layer.

Five Objectives of Concrete Surface Preparation

• Remove coatings, adhesives, sealers, curing compounds, dirt, and contaminants.
• Remove laitance, weak concrete, and deteriorated surface material.
• Open the concrete surface as required by the membrane system.
• Create a uniform, manufacturer-approved concrete surface profile.
• Leave the surface clean, sound, dry as required, and ready for installation.

Surface preparation should accomplish all five objectives. Producing a rough surface without removing contamination is not sufficient. Cleaning the surface without producing the required profile is also insufficient.

Evaluate Before Selecting the Preparation Method

Preparation begins with an evaluation of the concrete, existing materials, project environment, and membrane requirements. The selected method must be capable of removing the unwanted material without creating unacceptable damage.

Evaluate the Concrete

• Surface strength and overall soundness
• Laitance, dusting, scaling, spalling, and freeze damage
• Cracks, joints, penetrations, drains, and embedded items
• Previous repairs, patches, and underlayments
• Surface hardness and aggregate type
• Slab thickness and reinforcement where relevant
• Moisture condition and active leakage
• Oil, chemical, salt, or biological contamination

Evaluate the Work Environment

• Occupied or operating facility
• Allowable dust, noise, vibration, and shutdown time
• Access for preparation and dust-collection equipment
• Electrical power and ventilation
• Fire, explosion, and hazardous-location restrictions
• Protection of equipment, products, and adjacent finishes
• Waste collection and disposal requirements
• Schedule between preparation and membrane installation

Concrete Surface Profile

The International Concrete Repair Institute uses Concrete Surface Profile comparators, commonly called ICRI CSP chips, to describe surface roughness. The profiles range from CSP 1, representing minimal roughness, through progressively rougher conditions.

The required CSP must come from the membrane manufacturer's current written instructions or the project specification. Moisture-mitigation membranes commonly require mechanical preparation, but the exact profile varies by system.

More Aggressive Is Not Always Better

A surface can be underprepared or overprepared. Insufficient preparation can leave laitance, contamination, and an inadequate profile. Excessive preparation can fracture the surface, expose large aggregate, create deep valleys, increase membrane consumption, and make the specified film thickness difficult to achieve.

The correct goal is the approved profile on sound concrete—not the roughest surface the equipment can produce.

Common Mechanical Preparation Methods

Shot Blasting

Shot blasting propels steel abrasive against the concrete and recovers the media and debris. It can provide efficient preparation of large open floor areas.

The resulting profile depends on machine type, abrasive size, travel speed, blast pattern, concrete hardness, and number of passes. Slow travel or repeated passes can create excessive profile, while fast travel may leave surface material behind.

Shot-Blasting Quality Concerns

• Unprepared strips between passes
• Heavy overlap lines
• Excessively deep profile
• Remaining curing compound or adhesive
• Poor preparation at edges and columns
• Steel shot left in joints, cracks, or corners
• Inconsistent profile caused by varying concrete hardness
• Dust or debris left after blasting

Diamond Grinding

Diamond grinding is useful for perimeters, doorways, equipment bases, small rooms, and areas inaccessible to a shot blaster. It may also remove coatings and adhesives when the proper tooling is selected.

A grinder can polish dense concrete or smear soft adhesive and oil across the surface. Inspect the result closely. A shiny surface or residue-filled pores may not provide the required condition.

The grinder and HEPA-filtered dust collection system must work together. An undersized or poorly maintained vacuum can release hazardous dust and leave contamination on the floor.

Removing Existing Coatings and Adhesives

Existing materials must be removed to the extent required by the mitigation-system manufacturer. Leaving a thin film or stain can create an unqualified intermediate layer between the membrane and concrete.

Adhesives containing asbestos or other hazardous materials require evaluation before disturbance. Do not grind an unidentified legacy flooring material or adhesive until required hazardous-material assessments have been completed.

Oil and Chemical Contamination

Oil and chemicals can penetrate below the visible concrete surface. Mechanical preparation may remove the surface while exposing additional contamination beneath it.

Grinding can also generate heat and spread oily material across the floor. Preparation should not continue blindly when contamination reappears or a dark, odorous, or greasy surface remains.

Contamination Investigation May Include

• Facility spill and maintenance records
• Visual and odor observations
• Water-break or wetting observations where approved
• Core or powder sampling
• Laboratory chemical analysis
• Adhesion testing of prepared trial areas
• Manufacturer review of the identified chemical exposure

Severe contamination may require removal and replacement of affected concrete rather than ordinary cleaning and grinding.

Laitance and Weak Concrete

Laitance is a weak layer containing fine particles that can develop at the concrete surface. It may look solid but lack the strength needed to support a bonded system.

Dusting, scaling, freeze damage, rain damage, improper finishing, and weak cement paste can create similar concerns. Preparation should continue until sound concrete is exposed.

When the required removal becomes deeper than anticipated, stop and notify the responsible party. Significant concrete repair may require an approved repair design and compatible materials.

Cracks and Joints

Cracks and joints should be evaluated before membrane installation. Surface preparation may reveal previously hidden cracking or enlarge deteriorated edges.

Edges, Corners, and Penetrations

Large floor areas often receive good preparation while perimeters, columns, curbs, drains, trenches, pipe penetrations, and equipment bases receive less attention. These locations are also common points of water entry and coating failure.

Use appropriate edge-preparation tools and inspect the transition between machine- prepared and hand-prepared areas. Avoid leaving smooth strips around walls and columns.

Cleaning After Mechanical Preparation

Mechanical preparation leaves dust, abrasive, and debris that must be removed before the membrane is installed. Use a suitable industrial HEPA-filtered vacuum and clean accessories.

Ordinary sweeping can redistribute fine dust. Compressed air can spread silica and contamination and may introduce oil or water. Wet cleaning may add moisture and should be used only when approved by the system manufacturer and project procedure.

Final Cleaning Should Address

• Open floor areas
• Cracks and joints
• Edges and corners
• Drains and penetrations
• Shot-blast media
• Grinding dust
• Debris lodged in surface profile
• Dust deposited on adjoining vertical surfaces

Inspecting the Prepared Surface

Surface preparation should be accepted before membrane material is mixed. Inspection must evaluate more than roughness.

Acceptance Questions

• Does the surface match the specified CSP range?
• Have coatings, adhesives, curing compounds, and sealers been removed?
• Is the exposed concrete sound?
• Are oil, chemicals, salts, and other contaminants absent or addressed?
• Are cracks and joints treated according to the approved detail?
• Are edges, corners, drains, and penetrations fully prepared?
• Is the surface free of dust and debris?
• Are moisture and environmental conditions acceptable?
• Has preparation revealed any new condition requiring review?
• Can the membrane be installed within the permitted preparation-to-application interval?

Concrete Surface Profile Comparison

Compare the prepared concrete directly with official ICRI CSP chips when a CSP range is specified. Photographs alone may not represent profile accurately because lighting, scale, and angle can make a surface appear rougher or smoother than it is.

Check multiple areas. The profile produced near walls, in corners, over hard aggregate, and over soft concrete may differ from the main floor.

Adhesion and Surface-Strength Testing

Pull-off testing may be required to evaluate the surface or an installed test system. ASTM D7234 addresses pull-off strength testing of coatings on concrete.

Record both the measured strength and the failure plane. A test that fails within weak concrete provides different information from a test that fails at the membrane-concrete interface.

Testing is destructive. The location, quantity, acceptance requirement, test procedure, and repair method should be defined before testing begins.

Time Between Preparation and Application

Prepared concrete can become contaminated again. Dust from another trade, forklift traffic, leaks, spills, condensation, and worker traffic can compromise the surface.

Install the membrane within the manufacturer's permitted time after preparation. If the prepared area is left exposed, protect it and reinspect it before application. Additional cleaning or repreparation may be required.

Silica and Preparation Safety

Grinding, shot blasting, scarifying, chipping, and other concrete work can generate respirable crystalline silica. Follow applicable OSHA requirements, the written exposure- control plan, and equipment instructions.

Use effective engineering controls, properly maintained HEPA-filtered dust collection, required respiratory protection, eye and hearing protection, protective clothing, and controlled work areas.

Other Preparation Hazards

• Electrical power and damaged cords
• Noise and vibration
• Moving machine parts
• Metal shot and flying debris
• Ergonomic strain and heavy equipment
• Trip hazards from hoses and cables
• Unknown coatings, adhesives, and chemicals
• Confined or poorly ventilated areas
• Interaction with facility traffic and production
• Embedded electrical, heating, plumbing, or post-tensioning systems

Surface-Preparation Quality-Control Plan

1. Review requirements. Confirm removal, CSP, soundness, cleanliness, repair, moisture, and environmental criteria.
2. Prepare a representative trial area. Adjust equipment and tooling until the required condition is achieved.
3. Establish the acceptance standard. Compare the trial area with CSP chips and obtain approval when required.
4. Control production preparation. Monitor travel speed, tooling, overlap, vacuum performance, and edge work.
5. Inspect continuously. Identify remaining materials, weak concrete, contamination, and inconsistent profile.
6. Complete repairs and detailing. Treat cracks, joints, penetrations, and damaged concrete according to approved procedures.
7. Perform final cleaning. Remove dust, abrasive, and debris from all surfaces and details.
8. Document acceptance. Record the area, method, equipment, CSP, observations, repairs, photographs, and approving parties.

Contractor Field Checklist

• Review the membrane manufacturer's preparation requirements.
• Identify the required ICRI CSP range.
• Evaluate existing coatings, adhesives, repairs, and contamination.
• Confirm hazardous-material assessments where needed.
• Select equipment capable of removal and profiling requirements.
• Establish a representative approved trial area.
• Use effective silica-dust controls.
• Remove unsound concrete and bond-inhibiting materials.
• Inspect cracks, joints, drains, edges, and penetrations.
• Vacuum the entire prepared surface thoroughly.
• Compare multiple locations with official CSP chips.
• Document preparation and repairs with photographs.
• Protect the accepted surface from recontamination.
• Reinspect immediately before membrane application.

Knowledge Check

Technical References

Use the editions required by the project specification and follow current written instructions issued by the specified system manufacturer.

• ICRI Guideline No. 310.2R - Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair.
• ASTM F3010-24 - Standard Practice for Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings.
• ICRI Guideline No. 710.3-2022 - Guide for the Mitigation of Moisture in Concrete Floor Slabs.
• ASTM D7234 - Standard Test Method for Pull-Off Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
• ASTM F710 - Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring.
• OSHA 29 CFR 1926.1153 - Respirable Crystalline Silica standard for construction.
• Current technical data sheets, installation instructions, safety data sheets, detail drawings, and warranty requirements issued by the specified moisture- mitigation, coating, repair, underlayment, adhesive, and flooring manufacturers.

These references provide technical guidance but do not replace the project specification, applicable regulations, hazardous-material assessments, manufacturer requirements, or evaluation by a qualified professional. Final preparation and installation decisions must be based on current documents and actual site conditions.