Walls Sweating After Painting: 5 Causes and Fixes

When you paint your walls, you want them to look and remain perfect for a long time afterward. So, when those same walls begin ‘sweating’ water, it can be very frustrating. But, what are some reasons that walls sweat after painting, and how do you fix them?

When walls start sweating after painting, it could be due to excess humidity in the room or improper insulation. It could also be down to the area painted and whether or not it was properly sealed. You can often fix these issues with dehumidifiers or adequately preparing the site before you begin.

In this article, I’ll be covering some of the reasons that cause walls to sweat after they’re painted and how to remedy these problems.

1. High Ambient Humidity

When your walls are very cool, it can trigger condensation. This may occur for a variety of reasons: maybe it just stopped raining, maybe you turned off your A/C and opened the windows, etc.

The main factor in this equation is humidity.

When your walls are colder than the ambient humid air, water forms or condensates on the walls. This is extremely annoying if you’ve just painted: you may even need to repaint or apply additional coats.

How To Fix

If you believe the cause is humidity, the first thing you should do is crank your air conditioner until the humidity falls or install a dehumidifier if you don’t have an AC unit.

If it’s cold outside, consider using a space heater and if there isn’t adequate ventilation, open a window or turn on a fan.

You may need to keep this up for a few days, depending on the level of humidity and damage caused.

2. Improperly Installed Insulation

Properly installed insulation is supposed to prevent walls from sweating. But if insulation isn’t properly installed, the walls can absorb heat from outdoors in the summer.

In most cases, it will be cooler in the house, so when the heat in the walls meets the cooler indoor air, condensation forms and makes the walls appear to sweat.

In the cooler winter months, this phenomenon reverses: the indoors are warmer, and the walls are colder. Again, condensation forms when they meet. If you paint during extremely cold or hot months without adequate ventilation, sweating is nearly inevitable.

The humidity indoors exacerbates walls sweating because you create the moisture through showering, breathing, and any other type of running water. The more water you run without ventilation, in essence, contributes to walls sweating.

How To Fix

Other than completely ripping out your insulation, which is needlessly troublesome and expensive, there’s a simple and easy way to solve this issue: ventilate your home.

Open windows, install fans and generally increase airflow. But, again, dehumidifiers will help a great deal, and even a small unit will work.

However, to fix the issue at its source, you might need to consider replacing your insulation for something of better quality and ensure it’s properly installed by a professional.

3. You Painted Your Bathroom

Bathrooms tend to sweat the most out of any room after they’re painted, and this is because there’s so much humidity in there. Even if you have a lot of airflow in the rest of your house, the volume of water that gets run in the bathroom makes it very humid.

How To Fix

The way to stop newly painted bathroom walls from sweating is to not run water in the room until the walls are completely dried.

Install fans, open any windows and consider a dehumidifier. While it’s necessary to shower and do other tasks in the bathroom, if you increase ventilation, the bathroom walls should dry in no time.

Also, always choose a paint that states it’s for use in the bathroom. These will have water and mildew-resistant properties that should help to seal the walls and prevent any sweating.

4. Surfactant Leaching

Surfactant leaching is a phenomenon that happens to certain kinds of paint when they’re drying, especially latex paint. Latex paint contains surfactants that normally slowly migrate to the paint’s surface as it dries. When newly applied latex paint comes in contact with humid air, the surfactants rise much more quickly than they’re supposed to.

If this happens, the paint will discolor from oily residue weeping from its surface. Blotches will appear as the paint ‘weeps.’

Depending on how humid it is, the splotching can be more or less severe: extremely humid air can permanently stain newly applied paint. This is why it’s especially vital to ventilate newly painted areas.

How To Fix

To fix surfactant leaching, simply wipe the surface with a damp cloth and ventilate the area. If you just noticed it happening and immediately take action, it should correct itself.

Permanent staining from surfactant leaching is rare unless you don’t notice it happening or deliberately ignore it, perhaps thinking it’s just water.

To protect against surfactant leaching, the first step is to use water-resistant paint that will resist humidity. Running air conditioners can help reduce ambient humidity, or you can opt to use a dehumidifier and open some windows.

5. Poorly Sealed Bricks/Concrete

Similar to poorly installed insulation, walls sweating can also happen if your house has a substantial amount of concrete or brick in its construction.

Concrete and brick need to be sealed when building a home to protect against moisture and humidity. This is especially common with basements where part of the wall is above grade: it’s common for such walls to not get sealed right during construction, and then they weep afterward.

Painting unsealed brick or concrete is very difficult unless you seal the walls beforehand because any difference in humidity can cause sweating.

How To Fix

The only way to stop brick and concrete walls from sweating after you paint is to start by applying a sealer to the exterior walls.

This will protect against moisture and its byproducts, like moss and mold growth.

It is possible to apply a sealant to your exterior walls, but this can only be done after you have fixed the moisture issues inside. Painting over wet bricks will lock that moisture inside, causing all kinds of damage, such as mold and even cracking as it spreads.

Final Thoughts

When your walls sweat after painting, it can be a real pain. Thankfully, most problems with sweating walls come from high humidity. So, unless you have surfactant leaching, most cases of sweating walls can be solved by cranking the A/C or ventilating the area.

Sources

• The Globe and Mail: Sweaty walls and pipes likely signal trouble
• Sydney Home Show: What to do when your walls start sweating!
• Benjamin Moore: Surfactant Leaching
• SFSafeGate: How to Seal Exterior Brick
• Performance-Painting: 5 Important Things to Remember Before Painting Brick