Some coatings employ pre-gel, or additional cross linking, mediated by a change of pH. Oxygen uptake and oxidative polymerisation, unblocking of blocked chemical reactions and other chemical polymerisation reactions can further strengthen the coating. Under normal circumstances a decorative latex paint will become touch dry in 10-30 minutes and will be hard enough to paint over in about 2 hours. This process requires the removal of water from the coating. Lack of air movement leads to the formation of stagnant layers of air saturated with water vapour adjacent to painted surfaces. Sheltered walls and horizontal or gently sloping surfaces are particularly prone to this effect.
Stagnant layers retard further evaporation of water from wet paint surfaces.
When painting must be done in cooler conditions it is better to paint on windy days. Incompletely dried films rehydrate when their surface temperature drops low enough to condense water out of adjacent air. This dew point is a function of temperature, relative humidity, and the electrolyte composition of the coating. Generally, electrolytes present in the coating have the effect of increasing the dew point temperature. Paints with low alkali soluble thickener, low dispersant and electrolyte levels have least effect on the dew point temperature.