solvent evaporation and humidity problem?

Question

if humidity levels cause a decrease in air pressure, why does an elevated humidity level slow the solvent evaporation process from paint films? wouldn't the drop in pressure promote a faster evaporation rate?

Answer 1

The drop in pressure is due to the mole weight of water (18) vs that of dry air (about 29). The more water vapor, the lower the pressure. The pressure difference is not very large, but the more water vapor you have in air, the less of other vapors can be accomodated.

Answer 2

The higher the humidity the slower paint will dry.