Inspection Must Occur Before the Membrane Disappears

Once an underlayment, adhesive, coating, or flooring material is installed, the moisture-mitigation membrane can no longer be inspected directly. Defects that could have been repaired easily become concealed beneath an expensive finished assembly.

The contractor should establish a formal membrane-inspection and acceptance step before allowing the next trade or system layer to proceed.

Understanding the Terminology

Why Pinholes Form

Pinholes can result from air escaping the concrete, insufficient membrane thickness, excessive rolling, surface porosity, contamination, foam, or bubbles that break before the material closes.

Common Causes

• Air escaping from porous concrete during substrate warming
• An excessively rough or open concrete surface
• Insufficient material applied over the measured area
• Failure to use a required primer or scratch coat
• Overworking the membrane with a roller
• Using an incorrect roller cover or squeegee
• Mixing air into the material at excessive speed
• Foam or bubbles remaining after mixing
• Oil, silicone, chemical, or cleaner contamination
• Dust or loose material trapped at the surface
• Applying material after its usable working time
• Rapid environmental or substrate-temperature changes

Outgassing From Concrete

Concrete contains air within its pore structure. When the substrate warms, that air can expand and move outward. If a wet membrane is present, the escaping air can form bubbles.

Some bubbles close while the material remains fluid. Others break and leave open pinholes or craters. A surface can therefore appear acceptable during placement and show defects later.

Application during stable or falling substrate temperatures may reduce outgassing when permitted by the manufacturer. Approved primers, scratch coats, application methods, and additional coats may also be used.

Where Defects Are Commonly Found

• Heavily profiled or porous concrete
• Edges and wall-floor transitions
• Corners and areas behind columns
• Cracks and repaired areas
• Construction joints and saw cuts
• Drains, trenches, and penetrations
• Application-section boundaries
• Squeegee and roller overlap lines
• Low areas where material collected
• High spots where the film was pulled thin
• Areas prepared with different equipment
• Locations where debris or traffic disturbed the wet film

Lighting Is an Inspection Tool

Pinholes and holidays can be difficult to see under ordinary overhead lighting. Use bright, portable lighting positioned at a low angle across the surface. Raking light can reveal bubbles, craters, texture changes, dry spots, debris, and damaged areas.

Inspect from more than one direction. Glossy membranes can reflect light and hide defects when viewed from only one position.

When to Inspect

Visual Inspection Procedure

1. Divide the floor into inspection sections. Use the same section numbers employed in the application records.
2. Provide adequate lighting. Use general illumination and portable low-angle lighting.
3. Walk a consistent pattern. Inspect the complete area rather than only visibly questionable locations.
4. Inspect the field. Look for pinholes, bubbles, craters, dry spots, texture changes, foam, contamination, and embedded debris.
5. Inspect every detail. Examine edges, walls, columns, cracks, joints, drains, penetrations, and terminations.
6. Mark each defect. Use an approved removable marker or floor-plan reference without contaminating the membrane.
7. Photograph representative conditions. Include location and scale where useful.
8. Prepare a repair list. Identify the defect type, location, and approved correction.
9. Reinspect every repair. Do not close the inspection record until repairs are accepted.

Coverage Records Support Inspection

Compare actual material use with the measured floor area. Unexpectedly low consumption can indicate underapplication even when the surface appears uniformly colored.

Unexpectedly high use may indicate excessive profile, concrete porosity, unusually thick application, waste, inaccurate area measurements, or material collecting in low areas.

Consumption records do not locate individual pinholes, but they provide important evidence when combined with visual inspection and other approved testing.

Wet-Film and Thickness Evaluation

Wet-film gauges may help evaluate coating thickness on relatively smooth surfaces. Rough concrete makes measurement more difficult because the film follows peaks and valleys.

Do not use an unapproved thickness method to claim compliance. Follow the membrane manufacturer's written procedure and recognize that coverage-per-kit control may be the primary field method for some systems.

If destructive thickness measurements or samples are required, establish the number, location, acceptance criteria, and repair procedure before testing.

Continuity and Holiday Testing on Concrete

ASTM D4787 addresses continuity verification of liquid or sheet linings applied to concrete substrates. The method, equipment, voltage, grounding, substrate condition, and lining thickness must be appropriate for the installed system.

Electrical holiday detection commonly depends on a conductive path between the test electrode and the substrate or another grounded conductor. Concrete conductivity can vary with moisture, density, salts, thickness, reinforcement, and grounding arrangements.

Not every moisture-mitigation membrane is suitable for electrical holiday testing. Thin membranes, conductive fillers, broadcast aggregate, damp surfaces, complex details, or unsuitable equipment can produce unreliable results or damage the film.

Low-Voltage Versus High-Voltage Testing

Standards developed for pipeline coatings or conductive metal substrates should not be transferred automatically to a thin floor membrane over concrete. Use the procedure applicable to the actual lining and substrate.

Establishing the Test Procedure

When electrical continuity testing is required, the written procedure should be approved before the membrane is installed.

The Procedure Should Define

• The governing standard and edition
• Membrane product and expected thickness
• Permitted cure stage before testing
• Detector type and model
• Low-voltage or high-voltage method
• Required voltage or instrument setting
• Grounding method
• Electrode, sponge, brush, or probe configuration
• Wetting solution when applicable
• Travel speed and overlap
• Instrument calibration or functional verification
• Defect-marking method
• Repair and retest procedure
• Safety controls and qualified personnel

Instrument Verification

Check the detector according to the manufacturer's instructions before testing and at required intervals. Verify that the alarm functions and the grounding connection is effective.

A detector that does not respond to a known test condition cannot provide reliable inspection results. Document the equipment identification, settings, verification, and operator.

Repairing Pinholes and Holidays

Repair procedures vary with membrane chemistry, cure stage, recoat window, defect type, and surrounding condition. Follow the manufacturer's written instructions.

1. Mark and document the defect. Record its location, type, and size.
2. Determine the cause. Check for outgassing, contamination, soft material, thin film, damage, or a recurring substrate condition.
3. Remove unsound material. Do not coat over soft, unbonded, or contaminated membrane.
4. Prepare the repair area. Clean or abrade it as required without damaging surrounding sound membrane.
5. Apply compatible repair material. Maintain required overlap, thickness, and detailing.
6. Allow proper cure. Protect the repair from traffic, moisture, condensation, and contamination.
7. Reinspect and retest. Confirm that the defect is closed before the next system layer is installed.

When a Second Coat May Be Required

Widespread pinholing or excessive porosity may require more than isolated spot repairs. A manufacturer-approved additional coat may be necessary.

Before applying another coat, confirm surface preparation, recoat window, cleanliness, required abrasion, primer, coverage, and compatibility. An additional coat should not be used to hide soft material, contamination, or poor adhesion.

Inspecting Repairs, Joints, and Details

Repairs and transitions deserve the same inspection as the open floor. Check that crack-repair materials remain bonded, moving joints are honored, drain details remain open and functional, and penetrations are sealed according to the approved design.

Watch for thin edges, abrupt terminations, uncoated vertical faces, wrinkles, voids, bridging, and missed corners.

Soft or Uncured Membrane

Soft, sticky, rubbery, or discolored areas may indicate incorrect mix ratio, incomplete mixing, expired material, contamination, low temperature, or material applied after its working time.

Do not apply another layer over an unexplained soft area. Mark and isolate it, review the batch and mixing records, and obtain approved corrective direction.

Blush, Haze, and Surface Contamination

Some resin systems can develop a surface film, haze, blush, or contamination during cure. This can interfere with adhesion of the next layer.

Do not assume that abrasion alone or a solvent wipe will correct the condition. Follow the manufacturer's specific cleaning, preparation, and recoat procedure.

Final Acceptance Documentation

Record the Following

• Project, date, floor area, and inspection-section numbers
• Inspector's name and qualification
• Membrane product, batches, and installation date
• Actual material consumption and covered area
• Environmental conditions during installation and inspection
• Visual-inspection method and lighting
• Pinholes, holidays, bubbles, soft areas, and other defects located
• Floor plan showing defect and repair locations
• Photographs of representative defects and repairs
• Electrical continuity procedure and approval when used
• Detector model, serial number, settings, and verification
• Repair materials and procedures
• Repair cure and reinspection results
• Final acceptance date and approving parties

Membrane Acceptance Checklist

• The entire membrane surface has been inspected systematically.
• Edges, corners, walls, columns, drains, and penetrations are continuous.
• Cracks and joints match the approved details.
• No open pinholes, holidays, craters, or dry spots remain.
• No unexplained bubbles, fish eyes, or delaminated areas remain.
• No soft, sticky, uncured, or contaminated membrane remains.
• Material consumption agrees with the required coverage.
• Required continuity testing has been completed and documented.
• Every defect has been repaired and reinspected.
• The membrane is within the permitted recoat condition.
• The accepted surface is protected from traffic and contamination.
• Written acceptance is complete before the next layer begins.

Safety During Continuity Testing

Electrical holiday detectors can present shock, ignition, and equipment hazards. High-voltage instruments require properly trained personnel and manufacturer-approved procedures.

Do not use electrical test equipment in flammable atmospheres or near uncured materials containing ignitable vapors unless the complete operation has been evaluated and approved. Follow equipment instructions, site electrical requirements, grounding procedures, and applicable safety rules.

Wet-sponge testing introduces water onto the membrane. Control slip hazards, protect electrical equipment, and remove residual moisture before subsequent coating work.

Knowledge Check

Technical References

Use the editions required by the project specification and follow current written instructions issued by the membrane and test-equipment manufacturers.

• ASTM D4787-24 - Standard Practice for Continuity Verification of Liquid or Sheet Linings Applied to Concrete Substrates.
• ASTM F3010-24 - Standard Practice for Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings.
• ASTM G62-23 - Standard Test Methods for Holiday Detection of Coatings Used to Protect Pipelines. Its applicability is limited to its scope and should not be transferred automatically to concrete-floor membranes.
• AMPP SP0188 - Discontinuity Holiday Testing of New Protective Coatings on Conductive Substrates.
• ICRI Guideline No. 710.3-2022 - Guide for the Mitigation of Moisture in Concrete Floor Slabs.
• Current technical data sheets, inspection procedures, application instructions, safety data sheets, detail drawings, and repair requirements issued by the specified moisture-mitigation and flooring-system manufacturers.

These references provide technical guidance but do not replace the project specification, applicable safety requirements, manufacturer instructions, or evaluation by a qualified professional. Final inspection and continuity-testing procedures must be approved for the specific membrane, substrate, thickness, and project conditions.