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Weather Conditions Paint is not a finished product until it has been applied and dried on an appropriate substrate at the designed performance film thickness. Proper application therefore is critical to the performance of the paint system. High performance paint systems are especially sensitive to misapplication and a knowledge of the application characteristics and recommended film thicknesses are vital to obtain optimum results. Weather Conditions Bad weather conditions are a perennial hazard in painting operations. Paint should never be applied on wet surfaces and therefore painting should be avoided not only in rain,sleet and fog but also when high humidities and low steel temperatures lead to condensation. Condensation is very difficult to detect on surfaces and will occur if the steel temperature is below atmospheric dew point. As a general guide, application should not take place when the steel surface temperature is less than 3 °C above the dew point. Extreme temperature too may present problems. At low temperatures (below 5 °C), the curing of paints such as epoxies may slow down dramatically and for some paints stop altogether. Others are not seriously affected and chlorinated rubber -and vinyl paints may be used at or below 0 °C as long as the surface is free form ice -as ice may be present in pores of the steel surface at these temperatures, generally however, painting below 1 °C should be discouraged. At high temperatures, solvent loss from paint atomised during application is very rapid, paint droplets do not coalesce on the surface (leading to a porous coat)and clouds of dry spray may also be produced. The problem may be rectified by the addition of thinners but these should never be more than a few per cent of the weight of the paint. Generally, painting should be avoided during extremely hot hours where paint operations are carried out in hot climates, the paint should be applied in the morning and early evening.