Several factors affect the drying time of latex paint. The humidity and temperature when the paint is applied has a significant effect. The method of application makes a difference, as does the sheen and even paint color. The directions on the label give you a general idea of how long latex paint needs to dry between coats, but sometimes you need to wait longer than suggested.
Understand Drying Time and Curing Time: While latex paint usually dries to the touch within an hour (meaning lightly running your finger over it does not mar the paint) it can take up to a month to cure to its final hard finish. This is because latex paint forms a dry skin on the surface but the underlying paint is still wet. The liquids in the paint must completely evaporate through the dry skin to be considered cured.
Re-coating too soon can affect the look and performance of your paint job, both in drying and curing rates.
Average Re-Coating Times: The general recommendation for drying time between coats is four hours for both interior and exterior latex (water-based) paints. However, take the temperature and humidity levels into consideration. For ideal drying times, the temperature should be 70 degrees F with 70% humidity or less, and a light breeze or sufficient air movement to help the paint liquids evaporate.
In cooler temperatures, or when the humidity is high, allow more time between coats. Re-coating too soon can result in an uneven sheen and very long curing times. Applying too many coats too close together can also make the paint bubble and blister as the underlying paint liquids force their way through the paint film.
Some properties in the paint itself affect drying time. Deep colors may take longer because of the higher amounts of tint in the paint. Flat paint dries slower than shinier paint. Latex dries more quickly on porous surfaces like drywall, and paint applied with a sprayer or heavy-napped roller usually produces a heavier, slower-drying film.
When in doubt, it’s wise to allow a little extra time for the paint to dry between coats. If the humidity level is very high, put a dehumidifier in the area to speed dying time. At humidity levels at 90 percent or higher, the paint may never dry and will certainly never cure.
Painting Over Latex Primer: Many primers are latex and some require different drying times than regular paint. Always read the label. Some latex primers should re-coated within 48 hours for maximum performance, while others can be re-coated any time after the recommended drying time.