Environmental Conditions, Dew Point, and Condensation Control

The Weather Is Part of the Lining System

A lining contractor controls material, equipment, and application technique, but the surrounding environment controls how the surface and material behave. Conditions that were acceptable when the shift began may become unacceptable before the first coat is completed.

A small amount of condensation on freshly blasted steel can cause flash rust or adhesion loss. High humidity may slow cure or contribute to surface defects. Cold material may become too viscous to mix and spray correctly. Excessive heat may shorten pot life and working time.

The Four Basic Measurements

Most coating and lining projects require the contractor to monitor four fundamental conditions.

Material temperature should also be measured when required. The lining can be much colder or warmer than the surrounding air because of storage conditions, direct sunlight, heaters, or heated plural-component equipment.

What Is Dew Point?

Dew point is the temperature at which the air becomes saturated and water begins to condense. If a steel or concrete surface reaches the dew-point temperature, moisture can form on that surface.

The moisture may be too thin to see. The surface can appear dry while a microscopic film of water interferes with primer wetting and adhesion.

Contractors therefore compare surface temperature with calculated dew point. The difference between those two temperatures is commonly called the dew-point spread or surface-temperature margin.

Why Condensation Can Appear Suddenly

Condensation risk changes whenever air temperature, surface temperature, or humidity changes. A tank shell may remain cold while warmer humid air enters through an open manway. Moisture can then condense on the colder steel.

Common causes of sudden condensation include:

• Warm humid air entering a cold tank
• Nighttime cooling of exterior steel
• Morning temperature changes
• Rain or a passing weather front
• Starting or stopping heaters
• Opening access points or containment
• Changing ventilation rates
• Cold product, water, or soil behind a surface
• Direct sunlight heating only part of a structure

Readings taken in one location may not represent a large tank, containment area, shaded wall, floor, roof, or exterior shell.

Surface Temperature Is Not Air Temperature

Steel responds quickly to sunlight, wind, night cooling, cold contents, and external weather. Concrete changes temperature more slowly but can remain cold long after the surrounding air warms.

A thermometer hanging inside a tank only measures air temperature. It does not prove that the tank floor, lower shell, roof, concrete wall, or shaded area is within the permitted range.

Measure the actual substrate at representative locations. Include suspected cold spots, shaded areas, exterior-facing walls, floors in contact with soil, and areas near openings.

Relative Humidity and Lining Performance

Relative humidity affects condensation risk, solvent evaporation, water evaporation, surface preparation, cure, and worker conditions. Product sensitivity varies.

High humidity may:

• Increase the probability of condensation
• Promote flash rust on prepared steel
• Slow evaporation and extend cure
• Contribute to amine blush in some epoxy systems
• Interfere with moisture-sensitive materials
• Reduce visibility and ventilation effectiveness

Very low humidity and high airflow can also create problems for waterborne, cementitious, or moisture-dependent systems by accelerating surface drying. Always use the limits for the specific product.

Material and Substrate Temperature

Cold material generally becomes more viscous and may be difficult to mix, pump, atomize, spread, or consolidate. Cold substrates can slow cure and increase condensation risk.

Excessive heat can shorten pot life, reduce working time, increase solvent release, cause dry spray, create excessive exotherm, and make wet-film control difficult.

Heating only the air may not adequately warm a heavy steel structure or thick concrete slab. Likewise, direct-fired heaters may introduce moisture and combustion products if they are unsuitable or improperly vented.

Measuring Environmental Conditions

Instruments may include electronic environmental meters, psychrometers, surface-temperature probes, infrared thermometers, and data loggers.

Whatever instruments are used, the contractor should:

• Use equipment suitable for the required accuracy and range
• Verify calibration according to the project requirements
• Allow instruments sufficient time to stabilize
• Keep sensors clean and protected from overspray
• Take measurements near the actual work
• Check several locations on large or divided surfaces
• Record the instrument identification
• Recheck suspicious or rapidly changing readings

Infrared instruments can be affected by surface emissivity, distance, angle, reflected heat, and instrument settings. A contact probe may be required to confirm questionable readings.

Where Measurements Should Be Taken

Conditions can vary inside the same structure. Air entering a manway may be warm and humid while the lower steel remains cold. A tank roof exposed to sunlight may be much hotter than the shaded shell.

Representative measurement locations may include:

• Top, middle, and bottom of tanks and vessels
• Floors and walls in contact with soil or water
• Shaded and sun-exposed surfaces
• Areas near ventilation supply and exhaust openings
• Dead-air spaces and areas behind structural members
• Recently washed or repaired concrete
• Areas closest to operating equipment or exterior weather

How Often Conditions Should Be Recorded

Record conditions before surface preparation, before coating begins, and at the intervals required by the specification. Additional readings should be taken whenever conditions may have changed.

Recheck after:

• Weather changes
• Starting or stopping ventilation
• Starting or stopping heaters or dehumidifiers
• Opening or closing access points
• Moving to another area of the structure
• Work stoppages and meal breaks
• Unexpected changes in cure or application behavior

Continuous electronic logging can provide valuable information, but sensors must be positioned and maintained correctly. Data should still be reviewed by a responsible person.

Ventilation Changes the Environment

Ventilation removes vapor, aerosol, dust, heat, and hazardous contaminants. It can also introduce humid air, cold air, dust, or uncontrolled temperature changes.

Airflow should be designed to:

• Protect workers and support required atmospheric conditions
• Remove vapor and overspray from the work area
• Avoid dead-air pockets
• Prevent contaminated air from returning to the work
• Avoid disturbing wet lining
• Prevent excessive solvent concentration at the surface
• Maintain acceptable conditions throughout cure

Ventilation required for worker protection must never be reduced simply to improve coating application. The application plan must satisfy both safety and lining requirements.

Dehumidification

Dehumidification can help maintain prepared steel, reduce condensation risk, and extend the safe working window. It is especially useful in tanks, vessels, containment systems, and enclosed structures.

A dehumidification system must be sized and arranged for the enclosure, outside air leakage, moisture load, access openings, ventilation requirements, and project conditions.

Supply and return ducts should distribute conditioned air throughout the work area without creating untreated pockets. The contractor should monitor actual conditions at the surface rather than assuming that equipment operation guarantees compliance.

Heating the Work Area

Heating may be needed to keep the substrate and lining within their permitted temperature ranges. The heat source must be suitable for the coating materials, atmosphere, and work location.

Direct-fired combustion heaters can add moisture and combustion byproducts to the air. Improper heaters may also introduce ignition sources into an area containing flammable vapor.

Heating equipment, fuel, exhaust, clearances, electrical classification, and fire protection must comply with the site safety plan and applicable requirements.

Conditions Must Remain Acceptable During Cure

Acceptable conditions at application do not guarantee a successful cure. Temperature can fall overnight, humidity can rise, ventilation can be shut down, or condensation can develop before the lining has cured.

The contractor must maintain the required conditions for the complete period specified by the manufacturer. This may include the period between coats and the final cure before immersion or chemical service.

Amine Blush and Surface Contamination

Certain epoxy systems may develop a greasy, waxy, cloudy, or water-soluble surface film under particular humidity and cure conditions. This is commonly called amine blush.

Blush can interfere with adhesion between coats. Sanding alone may spread or drive water-soluble contamination into the surface. Follow the manufacturer's cleaning and recoat procedure before applying another coat.

Not every surface defect is amine blush. Confirm the condition before selecting a corrective method.

When Work Should Stop

What to Do After Conditions Become Unacceptable

1. Stop the affected operation.
2. Protect mixed material and equipment according to the manufacturer's instructions.
3. Mark the last acceptable application area.
4. Document the time and environmental readings.
5. Inspect prepared and coated surfaces for moisture, flash rust, contamination, or cure problems.
6. Restore acceptable environmental conditions.
7. Repair or reprepare affected surfaces as required.
8. Obtain the required inspection release before restarting.

Do not simply wait for the meter to return to an acceptable number. First determine whether the surface was damaged or contaminated during the unacceptable period.

Environmental Inspection Records

A complete record should identify:

• Date, time, project, structure, and work area
• Air temperature
• Surface temperature and measurement location
• Relative humidity
• Calculated or measured dew point
• Surface-to-dew-point difference
• Material temperature when required
• Instrument identification and calibration status
• Ventilation, heating, and dehumidification status
• Weather and exterior conditions
• Work being performed at the time
• Corrective actions and restart authorization

Contractor Field Checklist

Knowledge Check

Key Takeaway