Coating Application and Environmental Conditions
Application quality depends on the environment at the steel surface, not the ambient weather station. Measure steel temperature, air temperature, relative humidity, and dew point at the work face. A common minimum is steel at least 5°F (about 3°C) above dew point; if the margin is smaller, condensation can form before or during cure. Do not apply over visible moisture, frost, or flash rust beyond the specification. Airless spray is typical for bridge work; plural-component equipment is used for fast-curing materials. Follow the data sheet for mixing, induction time, pot life, thinning, and recoat window. A frequent trap is adding thinner to extend pot life or improve atomization; that can violate VOC limits and alter sag or cure behavior. Another trap is applying the full coat before stripe coats at edges, welds, bolts, and back-to-back angles. Stripe those areas first, then spray the full coat within the recoat window. If the window is exceeded, the surface may need abrading or a tie coat; do not simply overcoat. Worked example: surface temperature is 50°F and dew point is 47°F. The margin is 3°F, below the 5°F minimum, so stop and improve conditions. Rule of thumb: if the gauge says the steel is close to dew point, treat it as wet, even if it looks dry.