Knowing when to paint is just as important as knowing what to paint. Painting under the best weather conditions, at optimum temperatures, and allowing adequate drying time ensures good surface adhesion.
Low temperatures and rain
Obviously, paint is not going to stick when it is raining. But, it is best to stop painting at least eight hours before anticipated showers. Some paint can labels go further, advising stopping 24 to 48 hours before an anticipated storm.
So often we believe paint is dry because it feels dry to the touch. While latex paint may feel dry to the touch in two to four hours, rain can still dilute paint that is not really dry.
Because the adhesion of latex paint is dependent on its water base evaporating, low temperatures slow drying time. Most manufacturers advise not painting when the temperature is below 50 degrees Fahrenheit. The only time it is considered safe to paint at a lower temperature is if the temperature is going to rise doing the day to 70 degrees or so.
It is best to stop painting when temperatures start to drop for the day. As the temperature drops, the amount of water the air can hold lessens. The dew point is the temperature at which water vapor in the air begins to condense. Condensation can cause incompletely dried paint films to rehydrate, often causing the paint to run or blister.
Painted surfaces that have gone through prolonged drying times due to weather or temperature never achieve typical durability. For example, if the paint is still wet, paint film freezes. Coloalescence — the process of the paint resin squeezing together with paint pigments to form the paint film is interrupted. As the temperature rises, water will resume evaporating from the paint, leaving random particles of uncoalesced resin that literally washes away during heavy rains.
High temperatures and wind
Painting at high temperatures also causes poor surface adhesion. While paint labels indicate the optimum temperature to paint is between 65 to 85 degrees Fahrenheit, it is important to avoid painting a surface that is hot from direct sun exposure. Painting hot surfaces prevents the paint from flowing evenly off the brush or roller. The paint strokes will not look even. The paint film may blister — lift off from the underlying surface. Blistering is literally small vapor pockets created when the paint ingredients separate and vaporize.
Drying times and second coats
While painting in windy conditions may speed up the drying time, paint that dries too quickly may crack and flake off. Airborne dust particles will also interfere with the paint’s adhesion.
Because a coat of paint makes a dramatic aesthetic improvement to a home the tendency is to want to get the job done quickly. Unfortunately, when paint is dry to the touch it is not dry enough for a second coat.
The labels on primers and latex paint suggest the minimum drying time before re-coating. Many latex primers suggest waiting a minimum of three hours before applying the surface coat and many latex paint labels suggest allowing at least four to eight hours to pass between applying a first and second coat of paint. Applying the primer or paint thickly or painting at high humidity or cool temperatures will increase this time.
Adding a second coat to a surface that is not truly dry prevents air from reaching the underlying surface, keeping it from drying completely. This still-pliable first coat expands and contracts as the temperature changes. Alligatoring (small vertical and horizontal cracks that resemble the skin of an alligator) often occurs, causing the paint to flake off in rectangular chips. Painting over a soft coat can also cause the top coat to shift, which then dries into a rough crinkled surface that looks like wrinkled cotton fabric. Surfaces that are alligatored or wrinkled must be scraped or sanded down to the substrate and re-primed and re-painted.
Putting the newly painted surface into use
Finally, the paint can label will indicate when the paint surface is ready for use. Using a surface before at least 48-hours has passed can result in the paint taking on the imprint of objects laid on it.
Also, two freshly painted surfaces (such as windows or doorframes) can often stick together if used before they are dry.
The paint can label will explain how much time (often 14 to 30 days) that must pass before a newly painted surface can be scrubbed. Following the label instructions for optimum painting, conditions and drying times will ensure your paint job brings you pleasure for years to come.
Paulette Rossi is a Certified Master Recycler. She can be reached at: 503-797-1827 or firstname.lastname@example.org.