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For latex paint, the proper formation of the paint film (coalescence) can be seriously affected if paint is applied when air temperature is below 10˚C.
Curing may be incomplete and coalescence problems may arise, which can result in a paint film that fails prematurely or in the more serious cases, the paint film may crack and check. Improper film formation may cause a powdery film that can be brushed off the substrate. This can cause the touch-up coat to look several shades lighter than the base coat.
Chalky Coalescence Problems
Paint film failure
Even if the paint film appears sound, if the paint has poorly coalesced, extensive problems may arise when re-coating. In addition, the moisture level in the air typically increases as temperatures drop during the fall or are high in the early spring, which can cause large amounts of condensation to form on exposed surfaces.
If the condensation forms on a paint film that has not fully cured, it can cause surfactant bleed especially in deep or accent colours that result in soapy pinkish, amber or sometimes white streaks or blotches on the paint film. Condensation can also dramatically slow the dry time and cure time of the film, increasing the water sensitivity of the paint film until it has fully cured.
Alkyd/Oil based (solvent) finishes are more forgiving in regards to colder weather painting. These finishes cure by oxidation, not coalescence. Cold temperatures will retard oxidation, but are not detrimental to the overall curing of the system. Some alkyd finishes will still cure at temperatures near 0˚ C. Even though alkyd/oil base finishes will tolerate the lower temperatures of spring and fall, one still has to watch a couple key factors.
Cool temperatures along with high humidity can cause condensation. Condensation can alter the curing process or change the gloss of the finished paint job, be it alkyd or latex. Temperatures around the freezing point can produce frost formation on the paint job, which can be just as damaging as condensation.
Other factors to keep in mind when the exterior environment conditions are less than ideal include monitoring the substrate temperature. When surface temperature of the substrate is below 10˚ C it can significantly slow the drying time and even prevent proper film formation of the paint.
It is important to note that the surface temperature can vary between different areas on the same structure causing the dry time and proper film formation to vary as well. In addition, the actual temperature of the paint itself can be a determining factor in the success of a paint film as its performance is also affected the temperature of the paint when it is applied.
Store the paint in an area that will be at least 10˚C. If the paint is applied when it is too cold it will not flow properly, leading to excessive film build, thereby slowing the dry and cure time of the film.
It is important to have present the minimum painting conditions of 10˚C and humidity levels below 80% during application and up to 8 hours thereafter, otherwise the performance of the coating cannot be guaranteed. Click here to see why choosing Top Coat Painting for your project will make you look good!
