Painting Contractors: Interior Cold Weather Painting

The application of exterior paints in cold weather is an obvious problem, but interior applications but can also be difficult. Many people are reluctant to open windows to improve airflow due to the influx of cold air. The subsequent lack of ventilation causes solvent or water vapor levels to increase proportionately to the amount of paint applied.

With solvent products, this can constitute a health and safety hazard due to the level of fumes in the air and the personal exposure limits (PEL) of the solvent or solvent blend. It is difficult to monitor fume levels without complex equipment. Indicator pens generally have a wide variance range that can be influenced by ambient conditions and therefore are not generally considered reliable. Too often, applicators consider the odor level (through sense of smell) as an indication of fume levels. Unfortunately, most solvents can cause a de-sensitization of the ability to detect them.

Latex paints present different challenges with cold weather application. A lack of ventilation leads to a moist air build-up (i.e. humidity), with condensation appearing on all cold surfaces. This is most noticeable on the windows, but the exterior walls can also show a much lower temperature.

If condensation does occur on the exterior walls, this can lead to a slower drying with subsequent color and gloss variations. Thick film application or build-up in corners where air flow is generally the poorest, can cause mud-cracking of the finish. Even normal film thickness (4-6 mil WFT) if subjected to temperatures lower than the recommended limits (generally 10° C. (50° F.) during the initial drying period can result in poor film integrity and adhesion or color and gloss variations.

Lacquer coatings are prone to showing blushing and dull gloss when used in cool (and particularly in humid) conditions. The faster evaporating solvents used in nitrocellulose lacquers cause a cooling of the surface as they are leaving the film. This can lower the surface temperature just enough to dip below the dew point and start condensation on the surface, leading to blushing.

Open flame gas heaters produce moisture and raise the humidity significantly if they are used in an enclosed area or as the sole source of heat. This humidity can affect nitrocellulose lacquers, waterborne coatings and, where moisture is condensing on the walls, any type of coating. Dry, electric or radiant heat is preferred.

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