How To Treat Dampness In Internal Walls: 3 Step Guide UK (Do This!)

Homes should be cosy sanctuaries where one can unwind, away from the hustle and bustle of daily life. But when your internal walls are damp, this sanctuary is more of a source of stress than anything else. 

Treating dampness in internal walls could be as easy as applying a coat of waterproof (but breathable!) paint. However, some damp problems may require more extensive repairs. 

This guide will show you how to fix them.

How To Treat Dampness In Internal Walls

Many homeowners believe that damp internal walls are a result of condensation. However, there are other potential causes. Isolating the cause is paramount to solving the issue permanently.

1. Isolate The Cause 

The first step to damp proofing walls internally is identifying the damp type. There are four potential reasons for damp walls: 


Condensation is the most frequent cause of damp internal walls in UK homes and the easiest to treat. 

It generally occurs due to insufficient ventilation, a lack of insulation, and poor habits, such as forgetting to turn on the extractor fan when showering or leaving the windows closed when cooking (especially if you don’t have a cooker hood). 

Signs of condensation include damp patches, water droplets on walls and other hard surfaces, mould and mildew stains, and peeling or flaking paint.

Penetrating Damp

Also known as lateral damp, penetrating damp is usually the result of water successfully finding a way from the outside of the building into your home. 

Older buildings made of porous masonry materials are more susceptible to penetrating damp. Cracks in render and masonry, moss on the roof, and other openings in roofs and walls are the main causes of this damp type. 

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However, it can also happen due to plumbing pipes leaking inside a wall.

Signs of penetrating damp include damp patches on walls and ceiling, damp staining on external walls, flaking or peeling paint, crumbly plaster, and black mould. 

You may also notice water dripping from the wall or ceiling when it rains or if a pipe is leaking.

Construction Damp 

Construction damp has the same signs as penetrating damp, but it is caused by a construction error.

Potential causes include defective or missing windowsills, non-breathable wall coatings, improperly installed or defective seals around doors and windows, and unsealed holes in walls where cables or pipes protrude. 

An error when rendering the house is also a potential cause of construction damp.

Rising Damp 

Rising damp is more frequent in old houses, even though it can happen in any building. It occurs when ground level water travels up through porous building materials, including brick, sandstone, and mortar.

A tide mark on your ground floor walls is the most common indicator of rising damp. This mark, sometimes referred to as salt damp, is caused by the soluble salts found in groundwater and the composition of masonry materials. 

Other signs of rising damp include damp patches on the lower portion of the walls, bubbling plaster, peeling or flaking paint, rotting flooring and skirting boards, and a musty smell.

2. Solve The Damp Problem

Once you’ve isolated the cause, select the appropriate damp wall treatment below to fix the problem.

How To Stop Condensation Problems

Increasing ventilation and insulating external walls, the basement, and the roof are the best methods to fight condensation.

You can insulate the walls internally or externally. 

Internal wall insulation is cheaper than external, and you could even fit the rigid insulation boards yourself. Panels are generally 100mm thick, so they will slightly reduce your floor area.

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Increasing air movement can be done in a number of ways. Opening the windows when cooking or after taking a shower can help get rid of vapour. 

You can also install a new or more powerful extractor fan or an externally vented cooker hood. Your clothes dryer and washer should also be vented externally. If possible, avoid drying your laundry indoors.

Keeping your home warm in winter and using dehumidifiers can also help fix condensation issues.

How To Stop Damp Coming Through Walls

The treatment of dampness inside the walls is slightly different depending on the cause. 

If you’re dealing with penetrating damp, check the pipes, drains, and gutters and make sure they are not blocked. Check the roof for missing tiles.

Check around your window and door frames for any damp spots or cracks. 

Inspect the walls externally for holes or cracks in the render. A cracked or loose flashing between the chimney stack and the roof could also let moisture in. 

If you’re suspecting a construction damp problem, check the roof insulation and make sure it’s installed correctly. 

Inspect the holes where cables or pipes enter the home. Check the doors and windows (including the windowsills) and make sure they are installed correctly. 

If you can’t identify the damp cause, hire a damp surveyor or contact your building association or local council. 

Once you’ve found the cause, take the appropriate steps or hire a contractor to fix it. Painting the external walls with a water seal product could also stop penetrating damp, if caused by porous masonry materials.

How To Stop Rising Damp 

The only way to treat rising damp in an old house – or in a new one, for that matter – is to create a new damp-proofing course.

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Injecting a chemical damp proofing course into the walls is the cheapest way to stop rising damp. This is done by drilling holes into the base of the walls (externally) and injecting the compound. 

If you have a basement, waterproofing it could also solve the problem. 

3. Repair The Walls

Whilst treating damp walls before painting is crucial for a quality finish so is repairing the walls once you’ve solved the damp problem.

The first step is to let them dry thoroughly. Increase ventilation and use a space heater or room dehumidifier to speed up the process.

Stripping the old paint might be necessary in case of extensive damage. Also, inspect the plaster and fill in any cracks or holes before treating the surface with an interior wall sealer. 

In case of mould, clean the walls with a solution of one-part bleach to four parts water. Wipe the affected areas with a rag, then dispose of the cloth in a bag to prevent spreading mould spores to other areas of your home.

Once the walls are repaired, apply a good primer and paint in the desired colour, using a waterproof but breathable emulsion.

What Are The Effects Of Dampness In Walls?

Dampness in walls must be treated promptly, and not only because living in a damp house is bad for your health. 

Moisture travelling through walls may soften the plaster and render, causing them to crumble. It also affects the paint finish and could lead to the disintegration of masonry materials. 

Eventually, dampness in walls can reduce the structural strength of your house.


Treating dampness in internal walls can be quick and cheap or a costlier and more extensive process, depending on the cause. We hope this guide can help you identify the source of moisture and fix the problem before it becomes a real danger.

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