The temperatures and the atmospheric moisture content are constantly in flux. It is important to plan any painting projects for a forecasted period when it is not too cold and the moisture content is not too high.
It is possible to paint in wet or cold weather; however, if the temperature is very low or the humidity is very high, the paint finish will be compromised, and you will need to spend more time rectifying it. 500F-900F is the optimal temperature range, and humidity should be lower than 70%.
A good quality paint finish is achieved by using the correct paint, preparing the surface, ensuring you have quality paint brushes and rollers, and most importantly, exercising patience. If the weather is too wet, the humidity is too high, or too cold, rather hold off on starting the project until the conditions are more favorable.
You Can Paint In Bad Weather
Two primary conditions affect the way paint dries which are.
- The humidity.
- The temperature.
The Weather Is Too Wet, Or The Humidity Is Too High
The ideal humidity levels for painting fall between 40% to 70%.
If the weather is too wet or the humidity levels are more than 70%, the paint finish will be affected, and the following issues may occur.
The Paint Will Leach
Latex or oil-based paints will leach and leave behind the white or brown streaks discussed above.
The Paint Will Lose Its Protective Qualities
If too much moisture is in the atmosphere (humidity), it will compromise the paint’s protective qualities.
The Paint Will Take Longer To Cure
If the humidity levels are too high, there will be more water in the air, which will impact the speed at which the moisture in the paint’s solvents evaporate and slow down the time it takes to cure, which will compromise the finish.
The Temperature Should Not Be Too Cold
While you can apply paint in cold weather, however, if it is too cold, the results will not be optimal.
If the paint is applied in conditions that are too cold, the life expectancy of the paint layer may be compromised.
If latex or oil-based paints are applied at temperatures below 500F (100C), it will compromise the curing process.
In addition, it will cause the surfactants (pigments, binders, solvents, and additives) to rise to the paint’s surface too quickly.
It will leave behind tell-tale white or brown streaks and staining in a process called leaching.
Too much moisture in the atmosphere (humidity) will also cause leaching.
If the paint you are applying is oil-based (enamel paint around window frames etc.), the oils that form the base of the paint change consistency and thicken.
It causes the paintbrush bristles to stiffen, making it harder to apply the paint, resulting in more paint being used and a reduced coverage area per gallon.
The conditions needed differ between internal and external walls. The optimal weather conditions for inside and outside walls are as follows.
Painting Internal Walls
Painting inside the structure is easier than on the outside.
The work surface should be protected from the elements, so the painter has more flexibility regarding the weather conditions.
While the optimal temperature still lies between 500F – 900F (100C and 320C), if the temperature is lower, the painter can try to heat the area using an artificial means (space heater, etc.).
In addition, if the area is protected, the paint can be applied irrespective of the wind speed.
Painting External Walls
There must be no precipitation (rain) when painting an external wall, and a light breeze is also a positive factor.
If the temperature is below 500F, the paint will take longer to dry and ultimately cure.
While the paint is wet, impurities such as dirt, dust, grime, bugs, and organic matter are caught in the wet paint and ruin the finish.
If it is raining while you paint an external wall, the paint may be washed off and leave a streaky finish that needs to be redone.
A rule of thumb of optimal weather in which to paint an outside wall is.
- Clear skies and sunny weather.
- A light breeze.
- Temperature ranging between 500F – 900F (100C and 320C).
- Humidity levels of no more than 70%.
What Causes Paint To Stick To A Wall?
Three steps occur when the paint is applied.
- In the first step, the wet paint must stick to the wall.
- Once applied, the paint dries to the touch.
- Once dried, it will still take a little while to cure fully.
How Does The Paint Stick To The Wall?
The paint adheres to the wall surface at a molecular level.
The molecules in the wall and the paint adhere together through Van der Waals forces.
The liquid paint binds inside the surface pores. The molecules in the paint form a bond with the molecules in the surface, which is being painted through a process called Van der Waals forces.
If the wall has a plaster surface, it is good practice to spray a mist onto the surface to be painted and then apply the paint, enabling the paint to flow into the surface pores.
If you don’t carry out this step, the paint may bind to itself and not the wall, resulting in the paint peeling off in sheets.
Once Applied, The Paint Dries To The Touch
The paint dries when the surfactants in the paint evaporate, leaving the painted surface dry to the touch – even though it is not 100% dry.
The initial drying takes a few hours unless the temperatures are too cold or the atmospheric humidity is too high.
If the temperature or humidity is not optimum, the initial drying process will take too long, which may compromise the final paint finish.
What Is Meant By The Paint Curing?
Once the paint has gone through the initial drying process, where the surface has dried to the touch, it will still take some time to cure fully.
Until the paint has cured, it will still be flexible, with a plastic feel to it.
As the paint cures, it goes through a further hardening process where it fully fuses to the painted surface, and the “plasticity” disappears, and it will feel solid to the touch.
It generally takes 5- 10 days to cure completely, depending on the temperature and humidity levels.
While it is possible to paint a structure in cold and wet weather, it won’t be easy at temperatures below 500F (100C), and the final finish will be compromised. Additionally, the paint will lose its protective qualities, which will result in it needing to be replaced early.
On the opposite end, if the humidity is too high (generally when temperatures are high), it will negatively affect the final result.