Finishing in Hot, Humid Climates

How Humidity Affects Coatings and Blast Work

Many coatings are sensitive to humidity during application and cure. High moisture can slow solvent release, cause blushing or haze in some clear and topcoat systems, interfere with the cure of moisture-sensitive chemistries, and leave waterborne coatings slow to flash. On the blast side, freshly cleaned steel can begin to rust quickly when humidity is high and the surface sits near the dew point. Coating data sheets typically set limits on relative humidity and the gap between surface temperature and dew point, so the finishing area needs a way to measure and control those conditions rather than hoping the weather cooperates.

• Measure air temperature, humidity and surface temperature at the work.
• Prime blasted steel promptly, and keep the path from blast to paint indoors.
• Store coatings and abrasives in conditioned or dry space.

Dehumidification for Blast Rooms and Booths

Dehumidification is often the most useful upgrade a humid-climate finishing area can make. Desiccant dehumidifiers are common for blast rooms and large enclosures because they remove moisture effectively even when air is warm and damp. Refrigerant-based units and conditioned make-up air are other options. For a booth that exhausts large volumes of air, conditioning all of the incoming air can be costly, so plants weigh where control is needed most: the blast room during and after blasting, the booth during spray and cure, or a holding area between them. Dehumidifiers need electrical service, ductwork into the enclosure and condensate or reactivation exhaust, all of which should be planned with the rest of the mechanical system.

• Size dehumidification around the space and the hours it must hold conditions.
• Coordinate dehumidifier ducting with booth airflow so they do not fight.
• Plan service access for filters and desiccant wheels.

Keeping Painters and Blasters Safe in the Heat

Operators in coveralls, hoods and respirators can overheat quickly in a hot building. Heat stress affects safety and finish quality. Options include cooling the make-up air going into the booth, using cooling devices on breathing air for blasters and painters, providing conditioned break areas nearby, and scheduling heavy blasting during cooler parts of the day. Good airflow in the booth also helps operators feel cooler while maintaining proper overspray capture. Plan these measures with your safety staff, since comfort and safety both affect how long operators can work productively. Shade and ventilation at the booth entrance and blast room door also help, since operators often stage parts and gear in those spots between cycles.

Corrosion on Rooftop Fans and Air Units

Moist, salty air is hard on rooftop exhaust fans, make-up air units, ductwork and stacks. Steel housings rust, fasteners seize, dampers stick and electrical connections corrode. Specifying coated or corrosion-resistant housings, stainless or coated fasteners, and sealed electrical enclosures helps equipment last longer. Regular inspection of rooftop units, belts, bearings, dampers and burners catches problems before they shut down production. Ductwork joints and roof curbs should be sealed against water intrusion, since leaks into a booth can spoil coatings and damage filters.

• Inspect rooftop fans and units on a regular schedule.
• Replace corroded fasteners and dampers before they fail.
• Seal curbs and duct joints against wind-driven rain.

Storm Season Readiness

Hurricanes and severe storms bring high winds, heavy rain and power outages. Rooftop units and exhaust stacks need secure anchoring and bracing appropriate for wind loads. Plan how to shut down the booth, blast room, burners and dehumidifiers safely ahead of a storm, and how to restart them afterward with checks for water intrusion, damaged filters and debris in fans. Keep spare filters, belts and fuses on hand, since supply can be disrupted after a storm. If a facility uses backup power, decide in advance which finishing loads, if any, will run on it. After the storm passes, check stack caps, roof curbs and duct seams for wind damage before running fans, since a loose cap or open seam can let rain straight into the booth plenum.