AirSprayTech Academy Certificate Program

Why Moisture Causes Coating and Flooring Failures

Article 01 of 20

Concrete can appear dry while still containing enough moisture to damage a coating, flooring adhesive, protective lining, or low-permeability membrane. Understanding how moisture contributes to failure is the first step toward selecting, installing, and documenting a successful system.

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Moisture Is Often Hidden

Moisture-related failures are among the most expensive and misunderstood problems in concrete coating and flooring work. The surface may look dry, feel dry, and even pass a quick surface check while substantial moisture remains within the concrete slab.

Concrete is porous. Its interconnected pores can hold liquid water, water vapor, and dissolved salts. When a relatively impermeable coating or flooring system is installed, moisture movement may become restricted at the bond line. The resulting chemical and physical conditions can weaken the system or separate it from the concrete.

Where the Moisture Comes From

Before selecting a coating or mitigation membrane, the contractor should investigate the source of the moisture. Different sources require different corrective actions.

How Moisture Contributes to Failure

Loss of Adhesion

Moisture at the concrete-coating interface can interfere with adhesion or weaken the surface layer of the concrete. If the bond becomes weaker than the stresses placed on the system, the coating, adhesive, membrane, or flooring material can delaminate.

High Alkalinity at the Bond Line

Moisture can transport alkaline compounds and soluble materials through concrete. When evaporation is restricted by a low-permeability system, an alkaline solution may accumulate at the interface. Some adhesives and coating components can soften, deteriorate, or lose adhesion under these conditions.

Osmotic Blistering

Soluble salts or other contaminants beneath a coating can attract water through the coating film. Pressure may then develop in isolated areas, forming fluid-filled blisters. Simply repairing the visible blisters without addressing the moisture and soluble contamination can result in another failure.

Hydrolysis and Chemical Degradation

Certain coating and adhesive components are susceptible to degradation when exposed to prolonged moisture and alkalinity. The affected material may soften, become sticky, discolor, or lose its ability to bond.

Efflorescence and Salt Deposits

Water moving through concrete can carry dissolved salts toward the surface. As the water evaporates, white crystalline deposits may remain. Efflorescence is evidence of moisture movement, although the visible deposit does not by itself identify the exact source or severity of the condition.

Microbial Growth

Moisture trapped within compatible organic materials can support microbial growth. Odor, staining, or biological contamination may occur in flooring assemblies, underlayment, wall-to-floor transitions, and other concealed locations.

Typical Warning Signs

• Blisters or bubbles in the coating or flooring system
• Delamination or hollow-sounding areas
• Peeling at joints, cracks, penetrations, or slab edges
• White deposits, efflorescence, or recurring surface salts
• Darkened concrete or unexplained damp areas
• Adhesive that is soft, wet, discolored, or chemically degraded
• Clouding, whitening, staining, or color changes
• Coating that remains soft or does not cure as expected
• Musty odors or evidence of microbial growth
• Recurring failure after localized repairs

Common Assumptions That Lead to Trouble

“The Surface Feels Dry”

Touching the surface evaluates only what can be felt at that moment. It does not measure internal relative humidity or establish the amount of moisture moving through the slab.

“The Slab Is Old, So It Must Be Dry”

Slab age does not guarantee suitability. An older slab can receive moisture from the ground, plumbing leaks, exterior water, cleaning, condensation, or a failed vapor retarder.

“The Concrete Has Cured for 28 Days”

The traditional 28-day reference relates primarily to concrete strength development under specified conditions. It does not prove that the slab has reached the moisture limits required for a coating or flooring installation.

“One Reading Represents the Entire Floor”

Moisture conditions can vary across a slab because of thickness, placement sequence, sunlight, HVAC operation, ground conditions, previous flooring, water exposure, and building configuration. Required test quantities and locations must be followed.

“A Plastic Sheet Test Clears the Slab”

The plastic sheet method can indicate the presence of moisture under the test conditions, but it is not a quantitative substitute for the testing required by a product manufacturer or project specification.

“A Moisture Barrier Stops Every Water Problem”

Moisture-mitigation systems have defined uses and limitations. A product intended to control moisture vapor emission may not be suitable for active leakage, moving cracks, hydrostatic pressure, contaminated concrete, or exterior water intrusion.

Testing Establishes Conditions, Not Guarantees

Moisture testing provides information about the slab at the test locations and at the time the tests are performed. Results should be compared with the written requirements of the complete system, including primers, adhesives, membranes, coatings, underlayments, and finished flooring.

Commonly referenced methods include in-situ relative-humidity testing, anhydrous calcium-chloride testing, and the plastic sheet practice. These methods do not measure the same property and should not be treated as interchangeable unless the governing documents expressly permit it.

Record the test method, instrument identification, calibration information, test locations, slab thickness where applicable, temperature, relative humidity, HVAC condition, test dates, results, and the acceptance criteria used.

The Contractor's Practical Responsibilities

• Review the project specification before estimating or beginning the work.
• Obtain the current technical data for every component of the proposed system.
• Identify the required moisture tests, quantities, locations, and acceptance limits.
• Confirm who is responsible for testing and who has authority to accept the results.
• Investigate visible moisture, leakage, efflorescence, staining, and previous failures.
• Map and photograph test locations so results can be traced to specific slab areas.
• Document ambient temperature, relative humidity, surface temperature, and dew point.
• Notify the responsible parties when results exceed published or specified limits.
• Obtain written approval for any moisture-mitigation system and its installation procedure.
• Retain test records, product data, batch information, daily reports, and photographs.

What a Moisture Failure Can Cost

A failed floor or coating is rarely limited to the price of replacement material. Corrective work can require demolition, disposal, mechanical preparation, moisture investigation, new mitigation materials, reinstallation, equipment relocation, and interruption of the owner's operations.

Failures in warehouses, cleanrooms, food-processing facilities, aircraft hangars, hospitals, laboratories, secondary-containment areas, and manufacturing plants can also create sanitation, contamination, safety, and production concerns. Documentation is therefore an important part of both quality control and contractor risk management.

Safety During Investigation and Testing

Drilling concrete for in-situ relative-humidity probes can expose workers to respirable crystalline silica and may encounter embedded electrical lines, heating systems, reinforcing steel, or other utilities. Follow the project safety plan, applicable regulations, and approved dust-control procedures. Use suitable drilling controls, HEPA-filtered collection equipment, personal protective equipment, and scanning or utility-location procedures where required.

Moisture-mitigation resins, primers, cleaners, and repair materials may introduce chemical, ventilation, ignition, skin-contact, and respiratory hazards. Review the current safety data sheet and manufacturer instructions before handling or applying any material.

Pre-Installation Moisture Review

• Is the building enclosed and operating under the required service conditions?
• Are the HVAC system and environmental conditions stable?
• Are there visible leaks, wet joints, damp walls, or standing water?
• Is an effective underslab vapor retarder known to be present?
• What flooring, coating, adhesive, or curing compound was previously installed?
• Has the required moisture testing been completed at the correct locations?
• Do the results satisfy every component manufacturer's published limits?
• Are soluble salts, alkalinity, surface strength, and contamination also being evaluated?
• Is the proposed mitigation system approved for the measured conditions?
• Have all findings, exceptions, and approvals been recorded in writing?

Knowledge Check

Technical References

The following documents provide important technical guidance. Always use the current edition required by the project documents and the system manufacturer.

• ASTM F2170 - Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes.
• ASTM F1869 - Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.
• ASTM D4263 - Standard Practice for Indicating Moisture in Concrete by the Plastic Sheet Method.
• ICRI Guideline No. 710.3 - Guide for the Mitigation of Moisture in Concrete Floor Slabs.
• Current technical data sheets, application instructions, and safety data sheets issued by the specified coating, flooring, adhesive, primer, and moisture-mitigation system manufacturers.

These references support professional decision-making but do not replace the project specification, governing regulations, manufacturer requirements, or evaluation by a qualified design professional. Final system selection and application must be based on the actual site conditions and written project requirements.