What Happens When You Paint in High Humidity?

Should You Even Bother to Paint if it’s Really  Humid Outside?

We’ve covered in a previous article how all paint is not created equal. Exterior paint, for instance, is made to withstand a lot more outdoor punishment.

What Happens When You Paint in High Humidity?

So, is it ok to paint when it’s humid? Most experts will recommend a specific temperature and humidity range in which it’s ideal for painting. A rule of thumb is that the temperature should be between 40F and 90F, or 5C and 32C, with 40 to 70 percent humidity. Of course, this varies wildly.

What about when conditions aren’t ideal? What happens when you paint in high humidity? Let’s go ahead and state the obvious: humidity is terrible news for painting, And it has something to do with paint drying.

A Good Answer Requires an Obvious Question: What is Paint?

At this point, it’s useful to look at what paint is made of.

Paint is made of three components:

  • The pigment makes the paint look like paint. It’s where the color comes from
  • The binder is there to make sure these pigments stick together, to the surface they are painted on, and gives paint it’s protective quality
  • The solvent’s job is to make it easier to apply the paint by making it thinner. This is necessary because the pigment and binder combined can make for a very sticky mess

When you apply paint to a surface, the solvent then starts to evaporate. You are now left with the pigment that evenly binds to the surface and a beautiful coat of paint. As you can see, the drying process is crucial for the paint to cling to the surface effectively. If it can’t do that fast enough, it won’t create a hard coat.

How Does Humidity Affect Paint?

Humidity wrecks the drying process of paint by introducing extra water into the equation. Usually, some humidity is acceptable. A little water won’t be a problem so long as it evaporates faster than the solvent in the paint. At best, you’ll have longer drying times. Sometimes you might get a few discoloured spots called surfactant leaching.

When you paint in high humidity, it introduces even more moisture. Too much water interferes with the drying process. What you end up with is moist gunk that won’t form a protective layer on the surface.

This effect is especially pronounced when you combine high humidity with low temperatures. This nasty combination will make condensation quickly form on your surface.

Humidity also works against you when you’re painting on wood. Wood quickly absorbs moisture from the air during humid days. This makes it harder for the paint to adhere to the wood’s surface. The result is paint that’s uneven and peels easily.

What Should the Humidity Be to Paint Outside?

Of course, there’s no such thing as no humidity. In fact, some moisture is necessary for easier painting. Too low a humidity level can make the paint dry faster, making it harder to apply even coats. Somewhere in the neighbourhood of 40 to  50 percent is a good range.

A piece of advice is to pick the ideal time of day to paint. The best would be to paint before the day begins to warm up, but not so early that morning dew is still present. Mid-morning would be a good starting point. Experiment with a few strokes and see how it goes!