Why Can’t You Paint Inside When It Rains? Our Answer

Weather can be so unpredictable. When you are all set for a weekend indoor painting job, the weather will not, in any way, be in your favor. When it rains outside, all the possibilities of completing the job end up in a train of thoughts.

  • Should I continue painting?
  • Will the paint hold well?
  • Is it worth continuing?

For a project that you only do every five to ten years, success is crucial because it can affect the coat’s longevity. So if you wonder why you can or cannot paint indoors when it rains, here is what you should know.

Painting Indoors Under Normal Condition

Under normal conditions, you do not have to worry about how the rain or humidity may prolong drying time or affect the paint adhesion. You can go on with the normal process of preparing and painting the surface. Simply clean and sand the surface to smoothen it. And you are ready to paint.

You can expect the paint to adhere well, as how it should with water or oil-based paint. Under normal weather, there are low levels of humidity. This only means that the paint would dry as expected. You do not have to worry about the failure of your painting job as long as you follow the painting procedures indoors.

Factors that Affect Drying of Paint

  • Humidity

Humidity levels tell how much water vapor flows in the air. If the air is too damp, the surface will be cold, and the paint will have trouble adhering to the surface.

  • Temperature

The temperature indoors affects the drying and curing time of your paint. Not only will it affect its adhesion and drying time, but it may also affect the paint’s consistency.

  • Type of Paint

Paint has different chemical compositions. Each one suits a more suitable surface.

Oil-based paint takes longer to dry than water-based paint.

  • Thickness of Paint

Thicker paints will take a longer time to dry. The same goes for uneven thickness, thicker or thinner coats will have different drying times.

  • Ventilation

Ventilation is a crucial part of drying painted surfaces indoors. Indoor space needs air circulation to speed up drying time. Also, ventilation reduces humidity levels. It helps blow off fumes and prevent the accumulation of dust and debris in the painted area.

  • Surface

The surface affects the drying time of the paint. Especially when you deal with a porous surface like wood, the possibility of absorbing the dampness of water vapor is high.

How the Rain and Humidity Affect Painting Surfaces Indoors?

1) Relationship Between Humidity and Rain

Raining increases the humidity levels inside a room. Even if it continuously rains outside for the entire day, you have to deal with longer drying time and, worst, uneven and sticky paint.

When the rainfalls drop into the ground, it releases water vapor into the air. This water vapor is the moisture in the air that we sometimes feel as something damp in the skin. When more water vapor releases into the air due to constant rain, the humidity levels increase.

When humidity increases indoors, it would be impractical to continue the painting job because it will not adhere well. You can paint indoors when the humidity levels go from 40 to 50% if you want to maximize your effort in painting.

2) The Role of Humidity

Humidity highly affects the drying time of paint indoors. If you paint in a highly humid area, let us say about 80%, the solvents and water in the paint would have trouble evaporating. Moreover, the paint may absorb the excess water vapor, leaving the coat tacky and challenging to dry.

On the other hand, extremely low humidity levels could cause the paint to crack and peel.

The ideal humidity level for indoor painting is around 40 to 50%. At this level, the air has enough water vapor to slow down the process, drying the paint evenly without causing it to feel tacky or sticky. The result? Even finish indoors.

Why Can’t You Paint Inside When It Rains?

Technically, you can paint indoors when it is raining. But continuing to paint under this condition will make or break your project. For this reason, you must know its consequences. Otherwise, you must take steps to control humidity in the room.

1) Adhesion issues

For the paint to bond to the surface, it must dry and harden properly. However, moisture could prevent proper adhesion.

The air becomes saturated with moisture. And water molecules react with the applied paint. It can make the paint thinner or runny.

If you are painting on wood, this can be problematic because wood absorbs moisture.

For concrete surfaces, it will take a longer time to adhere to the surface with increased humidity and moisture. In this condition, the paint could remain soft and tacky for longer hours than for concrete surfaces under normal weather.

And if you are painting on metal surfaces indoors, it can be crucial because metal reacts heavily to moisture. It can cause rust and corrosion. It may trap into the painted surface and serve as a barrier between the surface and the paint, which leads to adhesion issues.

2) Longer drying time

Having excessive moisture in the air prolongs drying time.

When it is raining, there is less ventilation indoors, and the movement of air is restricted. For this reason, the water vapor flows in a constrained manner, and evaporation takes place slower. The paint remains soft and takes longer to harden in this condition.

Wait for the surface to dry completely. Turn your air conditioner on or use a dehumidifier to control it indoors.

3) Paint blisters and bubbles

Paint blisters or bubbles form when the moisture traps between the surface and the coat. With too much of it escaping the layer of paint, expect lots of bubbles under the coat.

4) Uneven finish

Uneven finishes develop when you paint while it is raining. It happens because of humidity, possible paint dilution, or thickening of the paint. Sometimes, the excess moisture alters its consistency and thins out or thickens the paint.

5) Molds

Mold tends to develop under moist conditions. In general, mold develops in moisture within

24 to 48 hours. One thing you need to avoid when painting indoors is the growth of molds. As the paint takes longer to dry under humid conditions, the mold traps between the surface and the paint. When it does, there’s a huge possibility for the mold to grow and spread.

Can you still Paint Indoor Successfully when Raining?

You can still paint indoors successfully even it is raining but with a few hacks.

How do you Prepare the Surface for Indoor Painting when it is Raining?

When you do not have any choice or other days to paint, and the weather is not good, you can control the humidity indoors. Controlling the humidity helps you deal with the excess moisture inside and paint smoothly in rainy weather.

  • Turn the ceiling fans and ACs on

When you expect bad weather, turn your fans and ACs on the day before and after your schedule. Doing this measure will help you prepare the surface. The fans will help draw out the moisture from the air faster. The same goes for after painting. Increasing the ventilation and giving the air more ways to circulate will help draw the moist indoor air faster.

Turn the ACs on before, on, and after your painting day.

  • Use a dehumidifier

Dehumidifier draws indoor air into the room, cools it to condense the water vapor, and dries the air. The condensed water vapor is collected into a reservoir and circulates the dried air. The process reduces moist air indoors.

A humidifier sets an optimal environment for the paint to dry. By using a dehumidifier, you can prevent the paint from sagging and leaving an uneven finish.

It is worth noting that the efficacy of a dehumidifier depends on its capacity and room size. Make sure to use a dehumidifier that can control the moisture in the room. It will be useless to use a small dehumidifier in a large room.

Run the dehumidifier before, on, and after the day of painting

  • Turn on the heater during the winter

This measure goes for extremely cold weather like the winter. You don’t have to crank it extremely hot. Just keep it within 60°F. Do this a day before and after painting.

  • Open windows

Opening the windows increases circulation within the room. If the rain does not sprinkle indoors and into the project area, you can open the windows to draw moist air out and dry the air faster.

  • Wait patiently

Patience is the key, especially if you need to apply a second coat. You need more patience. Expect the first coat to dry longer when it is raining. But if you performed the tips in controlling humidity above, you may have to wait shorter. So before applying paint, prepare the surface by drying it completely, even if it is raining. And let the first coat dry thoroughly before applying the second coat.

Application of Paint is as Important as Curing Condition

Remember this. The way you apply the paint impacts how the paint adheres to the drying surface. You need a consistently clean and dried surface before and while painting and while the paint bonds and cures on the surface. Your attention to this process will make a difference in the success of this project.

And yes, rain can be a hindrance. But with a few tricks, you can pull off an indoor painting project smoothly, even if it rains.