If conditions are too hot, too cold, too humid, or too dry when you apply paint or primer, problems may result.

If conditions are too hot, too cold, too humid, or too dry when you apply paint or primer, problems may result.

  • 1

    Be Sure That Temperature and Humidity are Right Before You Paint

    There are many factors that will impact the long-term success of your painting project. Most of those factors are firmly in your control: proper surface preparation, choosing the best products, etc.

    But two of the factors that can help to make or break your project are not entirely in your control: temperature and humidity.

    If your painting project is inside, you’ll likely be able to control the temperature, and to a lesser degree, the humidity. But if your project is outside, you’ll be at the mercy of Mother Nature. You’ll have little control over the temperature and humidity beyond waiting for the right day to roll around.

    The right day is worth waiting for, though, because charging ahead on the wrong day can result in lots of problems.

    Here’s a general rule of thumb: if the weather is uncomfortable for you — too hot, too cold, too sticky, too dry — then it’s probably not a great day for painting. For specifics about choosing the best day for your project, and the problems that may befall if you choose the wrong day, read on.

  • 2

    Temperature

    How hot is too hot for painting?

    Generally, temperatures of 90° F or above are uncomfortable for most paints (and for most people!) Temperatures that are too warm will decrease the viscosity of the paint or primer to a less-than-optimum consistency. (Solvent-based products are most susceptible to the negative effects of high temperatures.)

    The problems you might encounter from applying paint or primer in too-hot temperatures include:

    • Poor hiding of underlying colors or blemishes
    • Runs
    • Sagging
    • Poor leveling (paint dries before it flows sufficiently to cover application marks left by brushes or rollers)

    Temperatures that are too warm may cause latex products to dry faster than desirable. That makes it difficult to apply the product to an area before the previously applied area has dried. The result can be visible lines showing in the overlap zones.

    Painting problems are also likely to result when the mercury falls to less than 50° F. The cold will cause solvent-based products to dry too slowly, resulting in problems such as sagging, wrinkling, and flashing (shiny or dull blotches).

    And the cold may impede the proper coalescing of the resins in latex-based products, causing poor adhesion and diminished durability.

  • 3

    Humidity

    Conditions of high humidity can retard the evaporation of solvents in oil-based paints, causing unevenness in the gloss of the finish. High humidity can also cause sagging of water-based products, and may lengthen drying time considerably. Avoid relative humidities greater than 70%.

    Low humidity (substantially below 50%) can cause water-based products to dry too quickly, particularly when painting porous masonry surfaces. You might be able to slow the drying process sufficiently by using a hose to dampen the surface before painting, or by waiting to paint an area when it’s in the shade.

  • 4

    Check the Forecast

    It’s important that you apply your products when the temperature and humidity are within acceptable ranges. But don’t forget to consider weather changes that might occur after you’ve finished painting, but before the paint has cured.

    Problems can result if either the temperature or humidity exceeds acceptable limits shortly after application — even if conditions were perfect when you applied the product.

    It’s ideal if the comfort range of humidity and temperature will hold during the first 24 hours after application. It’s also best if there will be no cycles of freezing and thawing during the first two weeks after application.