How to fix damp walls

Regardless of whether you own your home or rent it, damp walls are never good. At best, they make a room feel chilly and unwelcoming, and at worst, they can cause structural damage and health risks. Moisture can damage building materials and promote mould growth.

Fortunately, moisture can often be addressed and prevented without calling in professionals. In this text, our building protection experts present 5 causes of moisture problems and their solutions.

Humidity problems and their solutions

1- Capillary action

If you notice damp patches, paint bubbles, crumbling plaster or powdery deposits at the bottom of your walls, the problem is likely caused by capillary action.

Capillary action usually occurs in masonry walls that have a defective moisture barrier or none at all, although inadequate sub-floor ventilation and poor site drainage can also be contributing factors.

Foundations are often made of concrete, which is a fairly porous material. When the foundation is waterlogged, moisture can travel up tiny channels called capillaries into the house.


  • Improve drainage on your property. Make sure there is a slope to keep runoff away from your foundation when it rains or snows.
  • Have professionals cover your foundation with a waterproof membrane.
  • If you spot cracks in your foundation, seal them with polyurethane insulating foam.

2- Condensation

Condensation occurs when humid air accumulates inside a home. Poor ventilation is often the cause.


  • Make sure your ventilation system is working properly. If it’s not running efficiently, you may need to re-seal it with a sealant designed for HVAC systems.
  • If necessary, install fans or vents in rooms you think the moisture is coming from (kitchen, laundry room, bathrooms, etc.) so the humid air is removed from the house before it can cause problems.

3- Thermal bridges

Thermal bridges occur in buildings with poor insulation. The lack of insulation reduces the thermal resistance of the walls, and the temperature fluctuations can cause condensation.

In cavity walls, thermal bridges generally occur where insulation has been poorly installed or has sagged.


4- Leaks and cracks

There are a variety of leaks and cracks that could be responsible for damp walls. Some are more common than others.

For example, leaks or gaps in a roof can cause water infiltration that damages the insulation in the attic and stains the ceilings.

Cracks around the bathtub, shower or sink can also lead to humidity in the walls. Water can seep into tiny crevices and saturate structural materials.

Plumbing leaks are also often responsible for damp walls.


5- A building envelope that is not waterproof

Damp patches on the walls are usually caused by penetrating moisture, meaning that water from outside is seeping through the exterior cladding to the frame and walls.

For example, a masonry wall with damaged bricks and mortar can let moisture in and cause water infiltration.

If the damp patches are clustered around the windows and doors, it’s likely that rain is seeping in through gaps around the frames. If the moisture is under the opening, it may be because there is no drip edge under a sill.


  • Keep the exterior walls and cladding in good condition.
  • Caulk the spaces around openings with a door and window sealant.
  • Clear the drip grooves under the window sills.

To fix damp walls, you need the right products

Damp walls can have a variety of different causes. You need to identify the source in order to choose the appropriate solution.

Adfast waterproofing products can help you address many of the problems that cause moisture in walls. In order to find the product that best suits your needs, use our product selector or contact our experts for help. That way, you can make sure you get the desired results.