How long interior paint needs to dry depends on several factors. Most significant are the type of paint and the drying conditions. For a successful painting project, you need to know how long paint must dry before applying a second coat, using masking tape or cleaning the surfaces.The recommended drying and re-coating times for each type of paint or primer vary but will be noted on the product label.
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There are two basic types of interior paints. Water-based (latex) paint is the most common choice for painting walls, ceilings and trim because it is fast-drying and lower in odour. Oil-based (alkyd) paint is sometimes used for trim and woodwork. Primers may be oil- or water-based.
Factors Influencing Drying Time
Temperature and humidity have the biggest impact on drying time. Apply latex paints when the temperature is at least 10 degrees Celsius. The ideal temperature for drying is around 21.1 degrees C. Cooler temperatures will retard drying time. Alkyd paints can be applied at or just above freezing, but will dry exceedingly slowly in cold weather. The higher the humidity level for either type of paint, the slower it will dry, as the paint liquids take longer to evaporate. At humidity levels consistently over 90 per cent, the paint may never dry and will certainly never cure. If there is no natural breeze, use a fan or dehumidifier to speed drying time.
Drying and Curing Times
Paint is dry to the touch when you can lightly run your hand over the surface and it feels dry instead of slightly sticky. Under ideal drying conditions, latex paint is dry to the touch in about an hour and alkyd paint, in three to four hours. Latex paint may be re-coated in three to four hours, while alkyd paint typically requires at least eight hours before re-coating. Paint is cured when it reaches its final hardness. Here the paint types are reversed. Alkyd is usually fully cured in about three days, while latex paints are not considered cured for about 30 days. A simple test to determine if paint is cured is to press it with a fingernail. If the paint is cured, a fingernail will not leave a small indentation.
Problems and Solutions
Avoid cleaning walls, putting things on freshly painted shelves or window sills, and leaving doors or windows shut or raised in the same position, for about 30 days. Because latex paint takes so long to cure, doors and windows could stick, and wiping down a freshly painted wall could leave indelible smears. If your paint job requires putting masking tape on fresh paint to paint straight lines and protect wood trim, don't use regular masking tape because it can pull the paint from the surface. Purchase blue painter's tape instead, which is available in a "low tack" version for delicate surfaces. It might be tempting to put a second coat on latex paint as soon as it feels dry, instead of waiting several hours. However, you risk it drying to an uneven sheen, and it will also take longer to cure.
Latex paint can dry to the touch to quickly, yet compared to alkyd paints, take about 10 times longer to cure. The latex paint film dries from outside in. It quickly forms a dry skin, but the underlying paint is still wet. The liquids in the paint take a long time to evaporate through the dry skin. Only when all the moisture has evaporated is the paint considered cured. Alkyd paint dries from the inside out. The paint film adhering to the substrate dries first, while the surface of the paint film is the last to dry. Because it doesn't form an initial skin on the surface, the moisture and solvents evaporate faster, decreasing the cure time to about three days.
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