Wet walls: How to correctly spot & remove damp

Let's go! Our step-by-step guide on fixing moisture in walls

The following guide offers a simple and succinct explanation of what steps you need to take to spot and treat wet walls. You’ll find more detailed information further down in the “Tips & Planning” section of this guide.

1. Visually inspect the walls.
2. Measure the moisture levels in the walls with a suitable device, such as a thermo detector or a moisture meter for wooden walls. An inspection camera can also work.
3. Isolate the area of damp and find the cause. If necessary, consult a building expert.
4. If you are renting, inform the landlord immediately.
5. Remove the source of the damage and dry the wall.

Here are some of the most common types of wall dampness and the solutions to fix and prevent them:

Tips & planning for wet walls

Permanent dampness in a house not only damages its structure but can also affect the health of its occupants. The increased humidity can lead to respiratory and joint problems, particularly in older people and small children.

On top of this, damp walls are an ideal breeding ground for mould. Spores are released indoors, where they are absorbed through the air by humans and animals. This can cause anything from severe fatigue and headaches to allergies and asthma, which is why you should always act as soon as you spot dampness in a room!

How can I spot condensation on walls?

You can often detect a problem just by looking at and smelling the wall. You can spot damp if:

• There is a musty or earthy smell that doesn’t disappear even when ventilated.
• The room is cold and clammy, even if the heating is on.
• The windowpanes are permanently fogged.
• The affected wall feels colder than the rest of the interior walls.
• The wallpaper, tiles, or plaster is peeling off.
• Metal girders are rusting.
• Brickwork is crumbling and there are small cracks.
• There are mould stains and salt crystals present, as damp dissolves the salts out of mineral building materials.
• There are floor puddles in the room.
• Mould formation is visible as black, brown, reddish or yellow stains.

How can I measure damp in masonry?

You can measure the dampness in a wall by using either a moisture meter (for wooden walls) or a thermo detector. Hold the device in front of or against the wall and take several readings in different places. The results will be displayed either as a percentage or in digits.

Moisture levels in cellar walls can even reach 150% or 200% if the masonry is unsealed or inadequately sealed. A wall’s material will determine whether it is considered damp or wet. You can find data on appropriate moisture levels for different building materials online. We also have a separate guide on determining a wall’s material.

You can also employ a specialist company to take professional moisture readings of your walls. This gives confirmation of your suspicions, provides more accurate results, and can determine the causes of the dampness in your walls.

To do this yourself, you can drill into your walls using a rotary hammer. . Check out our guide on drills for further details on finding the right drill for this task, or you can just leave it all to a professional. As with any DIY project, make sure you follow DIY safety precautions at all times.

Drilling holes also lets you measure the moisture in deeper layers of the building. You can collect samples from inside your walls and use them to determine the amount of dampness. Crush the sample into a pressure cylinder and mix it with calcium carbide. The ensuing chemical reaction provides information about the moisture content.

Causes of wet walls

Before you can renovate a damp or wet wall, you must first find out where the water is coming from. In most cases, one of the following causes is to blame:

• Poor ventilation: Showering, cooking and drying clothes produce a lot of indoor water vapour that needs letting out. A window that's permanently open but only on the latch doesn’t create enough air flow and cools down the masonry. Moisture then condensates on the cold surfaces.
• Incorrect heating: Too little heating can cause condensation to form on cold walls in winter and slowly penetrate the masonry.
• Technical faults: Dishwashers, dryers, washing machines and air conditioners (etc.) can leak water.
• Defective vertical protection: With no external waterproofing, ground water can seep into the masonry where it spreads further.
• Leaky or missing horizontal protection: If both the vertical and horizontal seals are missing, water can seep in through cracks in the wall. This problem usually goes unnoticed until moisture in the walls causes problems.
• Leaky or damaged roof: Cracks or holes in the roof will enable rainwater to drip through, penetrate the walls, and spread to multiple rooms.
• Thermal bridges caused by insufficient insulation: Thermal bridges are areas of the building where an abnormal amount of heat escapes. Moisture condenses in these areas. Shutters, blinds, window frames and lintels are often affected by this.
• Flooding and heavy rainfall.
• Damage to water a sewage pipes: Individual wet-looking spots on internal walls that spread quickly are sure signs of water damage. Usually, leaks are caused by corrosion, but pipes can also be damaged by DIYers who drill incorrectly. See our "first-aid" article on what to do if your drill hits a water pipe accidentally.
• Cracks in the masonry, through which moisture can enter.
• Poorly sealed showers and bathtubs: Running and splashing water can seep through cracks and gaps in your bathroom.
• Insufficient drying times in new buildings: Sometimes with new builds, not enough time is planned for the moisture to escape.

Water always looks for the path of least resistance to escape from. As such, it’s worth checking the building plan of the house. Which rooms share a common wall? Which rooms are on top of each other? Where are the pipes laid out?

If your walls are permanently wet, you should consult an experienced building expert. They will diagnose the problem and advise you on how to proceed.

Tips and remedies for wet walls in your house

Each of the causes mentioned above show different damage patterns and require specific measures. When draining the water, it’s important to also fix the source of the damage. Superficial treatment is only a short-term solution for wall dampness.

You can repair minor damage yourself. Wall dampness through a burst pipe or defective washing machine can be easily remedied by simply airing the room. A dehumidifier is recommended for smaller areas, as this draws the moisture out of the room and the wall.

For larger areas of water damage, however, special building dryers are used. Condenser and adsorption dryers are frequently used alongside infrared and radiant heaters. Radiant heaters work similarly to infrared heaters, but they penetrate deeper into the walls.

If condensation is forming on your walls in your bedroom, it’s time to reconsider your heating or ventilation behaviour. It’s better to ventilate briefly and intensively instead of leaving the windows permanently but slightly open. Intermittent ventilation (opening your windows completely three times a day for 5-10 minutes at a time) is the best way to dry your walls.

In addition to this, it’s good to regularly check the humidity in the room using a hygrometer. A reading of between 40% - 60% is ideal. Never place the hygrometer near heating appliances or windows, as this could skew the results.

Mistakes around heating are also common. Make sure that all rooms are heated to at least 15°C in winter, even the ones you don’t use. Frequent and significant temperature changes in your house or flat promote moisture damage.

If water gets into your walls through cracks or leaks, these must be closed immediately. Check out our DIY guide on repairing cracks in plaster for more information. Do you need to seal a flat roof or insulate an attic? We’ve got guides for those, too.

If mould appears on wet patches on your wall, you must act quickly to prevent it spreading further. Small and superficial stains can be tackled yourself with special mould removers, medical alcohol or methylated spirits. If mould has taken root in the building’s structure, however, you should call a specialist. Qualified support is also needed to spot and remove dry rot.

Stop wet walls: Masonry waterproofing

If your house or cellar’s waterproofing is damaged, intermittent ventilation and special drying appliances won’t be enough to protect the walls against moisture in the long term. Instead, you can use either horizontal or vertical protective barriers to dry out your walls. Horizontally installed barriers prevent moisture seeping up from the ground into the masonry, while vertical barriers protect against moisture that penetrates from the side.

Horizontal barriers can be created by:

• Cutting and sawing: Insert one or more insulating barriers (like metal sheeting, plastic boards or bitumen coating) into the wall. In general, this is taken care of in new buildings, but they can also be retrofitted into old buildings if the specifications of the house allow it. This requires the wall to be cut open with special tools.
• Chrome steel sheeting: Overlapping corrugated sheets are placed into a joint in the masonry with a jackhammer. You don’t need to open your walls for this, which means even an experienced DIYer can do it. Use special building dryers to remove the remaining moisture.
• Unpressurised injection: This method is also suitable for DIYers, provided only small areas are affected. Multiple holes are drilled into the wall and filled with a liquid sealant, which gradually spreads into the masonry and seals up any pores and cavities. We have a guide on drilling holes in concrete if you need help with this. In instances of heavy moisture penetration in the walls, you must first dry the masonry.
• Pressurised injection: Again, holes are drilled into the wall. This time, however, the chemical sealant is injected with a specialised machine under high pressure. This allows it to reach gaps that are otherwise difficult to access.
• Wall replacement: This elaborate method is mainly used for severely damaged masonry, and involves partially replacing the wet bricks, mortar, or concrete in the wall. To prevent the water from rising, it’s best to install a horizontal barrier beforehand, but this will be limited by the structure of the house.
• Electrophysical methods: In some cases, you can use an electrical voltage to displace moisture from the masonry. However, this method is relatively expensive, and the results are disputed by experts.

For vertical waterproofing barriers, the following options are available:

• Exterior waterproofing for basement walls: If you need to drain your wet walls from the outside, you must first completely expose your external basement walls. After repairing any faulty joints or plaster layers, a thick coat of bitumen is applied (referred to as a “black tank” across Europe). Dimpled sheet membrane and filter fleeces act as an additional protective layer. Alternative insulation methods include sealing slurries (brown tub) and plastic sealing sheeting (K-tub). If you seal your exterior basement walls carefully, the inside moisture should dry up on its own.
• Interior waterproofing for basement walls: In addition to exterior waterproofing, you should also treat damp walls from the inside. First dry the walls and remove any old plaster layers, then apply several layers of sealing slurry. If it’s not possible to waterproof your exterior wall, you can use special renovation plaster to refurbish the wet wall. This repels moisture from the outside but is diffusion-open from the inside. It’s also able to bind and store salts.

Costs for drying and renovating wet walls

The costs for wall drying depend on the extent of moisture penetration in the walls and the size of the area to be renovated. Here’s an overview of what you can expect:

If you have any damage assessed by a building expert, expect additional costs of around £60-85 per hour.

If you choose to do the work yourself, however, you can massively reduce the costs. As a DIYer, you can knock old plaster off walls, scrape out joints, expose basement walls and even paint the walls after they’ve been dried. Some advanced procedures can also be done yourself, such as unpressurised injections, chrome steel sheeting or applying special renovation plaster.

In the event of a burst water pipe, homeowners' insurance usually covers the damage. If the walls are wet due to flooding, additional insurance is required in advance to cover the damage. Damage caused by technical defects is covered by the household contents insurance.

Other renovation projects

Do you love a bit of renovation? If you’re interested in further renovation projects, we’ve got plenty of useful guides for you. Our DIY Knowledge section offers numerous tips and tutorials that you can use to spruce up your home, from sanding floorboards to covering a radiator.