Damp on Walls

Given the persistent rainfall across the UK, it’s no surprise that many homeowners experience problems with damp walls. From damp spots on walls to a persistent musty smell and damaged plaster, moisture can enter a property through various means including rising damp, penetrating damp, and condensation.

Sometimes damp patches can be caused by plumbing leaks, or issues with appliances like washing machines or dishwashers.

Whether you’re seeing dampness on walls internally or noticing damp patches on external walls, understanding the source is the first step toward effective damp repair.
Our expert guide explains the most common causes of wall dampness, how to identify the signs and type of damp, and the most effective damp treatment options.

If you are still unsure about the damp problem, you may require a damp survey by a trained professional who can provide you with advice and recommendations to help stop the problem.

Dampness can be caused by several factors, either moisture penetrating into the building from outside, through excessive moisture within the property, or through rising damp because of the lack of, or a defective damp proof course. These can be identified in different ways, giving you an indication of the problem, and how to solve it.

You may not even require damp proofing - often internal leaks from plumbing problems or broken appliances can cause damp problems. The first step is always to check pipework and seals to make sure that isn’t the source of the damp patches. Both water and waste pipes can be hidden within walls and leaks then come to the surface in unexpected places. If you find issues relating to plumbing leaks you should contact a plumber.

Because different types of damp require different treatments, it is very important to identify the type of damp causing the problem and solve it. If you misdiagnose the type of damp this could lead to the problem getting worse, and more costly repairs in the future.

It can be challenging to accurately identify the specific type of damp affecting your property yourself. A professional damp survey goes beyond just visible symptoms, using specialist equipment to help to pinpoint the exact cause and extent of the issue.

If you're unsure about the type of damp in your home, seeking expert advice can provide clarity and ensure the correct treatment is recommended.

Rising damp is caused by groundwater moving up through porous building materials by capillary action, affecting ground floor walls of properties. Key signs include damp tidemarks on internal walls, just above the skirting boards up to a metre high, and salt deposits that damage paint and plaster. You may also notice flaking paint and lifting wallpaper and a stale, damp odour.

Rising damp is often misdiagnosed and is more rare than people think. Rising damp will only ever affect ground level walls, up to a metre. If you notice damp problems elsewhere this indicates it is not rising damp.

Rising damp signs on internal walls are more common in older properties and terraced houses that do not have an existing damp proof course, or where the damp proof course has become defective.

Penetrating damp most commonly occurs due to wind driven rain when water enters the building from the outside. It can also be caused by building defects like porous masonry, damaged mortar joints, damaged gutters, cracked render, or broken downpipes. It is mostly an issue for solid wall rather than cavity wall properties.

Penetrating damp can affect any level of your home, and you may spot corresponding damp patches both inside and outside, near where there are building defects. Inside, dampness on the wall can appear as moisture patches, stains, or even mould growth. Moss and algae may grow externally around blocked drains, gutters and near broken downpipes.

If left untreated, these damp spots can damage plaster, leave water marks and create a cold, uncomfortable environment.

Condensation is the most common form of damp in the UK, affecting millions of homes, especially during the colder months. Condensation forms when warm, humid air comes into contact with cooler surfaces such as windows or cold external walls. This typically leads to black mould growth, often found in bathrooms, kitchens, and other areas with poor ventilation.

It will often affect north facing external walls as they receive little sun, and can appear behind large furniture such as wardrobes and sofas pushed up against walls. It is common near areas that produce moisture, such as kitchens and bathrooms. Ventilation must be improved to help remove the warm humid air from inside the home. Mould growth is most commonly caused by condensation, although it can be caused by penetrating damp.

Damp external walls often show visible signs of water ingress, such as moss growth, streaks, or salt efflorescence. In many cases, these symptoms mirror those found on interior walls, indicating the source of moisture is external.

Building defects like cracked render, poor pointing, or cavity wall insulation problems can contribute to damp on walls, particularly if moisture is being trapped or redirected.

Blocked gutters or backed up drains may cause heightened water levels, which can then penetrate into masonry.

If high ground levels are bridging damp proof courses this can also cause damp patches on walls. If newly installed pathways or flower beds are built up against the walls, moisture can bypass the damp proof course and enter the building. The construction method of a wall may affect the extent of a damp problem. Walls that are solid construction are more vulnerable to penetrating damp problems than cavity walls.

Whether you’re dealing with damp on an internal dividing wall, a damp internal wall in a terraced house, or dampness on outside walls, the correct damp repair method depends on the type of moisture problem.

Once you have correctly identified the cause of dampness, you should address the issue and remove the source of moisture. If left untreated, damp can make your property an unpleasant place to live, and could even lead to structural problems such as fungal decay.

If you are unsure about next steps, you may require professional advice. This will give you peace of mind a professional has fully investigated, and given you recommendations that will solve the problem long term.

Once confirmed as rising damp, the most effective solution is to install a remedial damp proof course (DPC).

This involves injecting a damp proof cream into the mortar joints of the affected wall, creating a waterproof barrier that stops the upward movement of moisture within the masonry.

Because plasterwork is often contaminated with hygroscopic salts that migrate into the wall from groundwater, plaster will need to be removed and then replastered with a salt retardant additive. If left, these salts will absorb moisture from the air, causing damp patches.

Begin by fixing the source of the moisture, such as broken roof tiles or leaking downpipes. These building defects are often easily fixed by DIY or remedial repairs from a builder. Brickwork may need repointing and if masonry is porous, masonry protection creams can be used to help create a waterproof barrier against wind driven rain.

Sometimes buildings can have high ground levels affecting the property, as may occur from access paths or basement walls.  A structural waterproofing solution will then be required. Depending on the scenario, we can assist in designing full waterproofing systems to BS8102 specifications.

If you have damp, wet walls and black mould growth, you may require improvements to ventilation, thermal improvements and a reduction in internal humidity.  This could mean using extractor fans, dehumidifiers, or installing a Positive Input Ventilation (PIV) system.

Mould will often form on cold walls, and this can be addressed by improving the thermal efficiency through thermal plastering and anti condensation paints. If you have problems on ceilings you may require insulation being topped up.

If the mould problem is regularly returning, and causing significant issues to your property, 
you may require a damp survey by a trained professional who can provide you with advice and recommendations to help stop the problem, which may include a professional mould clean.

Damp proof paints are options for specific damp problems, but may not address the root cause of the problem. If installed incorrectly they could even trap damp inside walls and mask the problem, causing further issues at a later date. A damp survey should be carried out to understand the damp problem, and provide recommendations for use.

For minor patches of condensation, anti-condensation paint can be applied to create a thermal barrier between the cold surface and the warm moist air. This can help prevent future mould growth. Condensation paints that contain a fungicide are also available. These prevent mould growth, but do not address the root cause and condensation may still form on the surface.

A masonry protection cream will create a water-repellant coating on porous masonry, therefore stopping penetrating damp caused by wind driven rain. The walls will be dry, meaning improved thermal efficiency as wet walls require more heat to warm. This can help reduce energy consumption and therefore energy bills.

Peter Cox can provide you with an expert damp survey if the problem is persisting and you would like professional advice.

Our network of branches across the country ensures that a local fully qualified surveyor will visit your property. We are backed by various trade bodies, providing assurances that we conform to and surpass the highest industry standards. Since our formation in 1951, we are proud to uphold our reputation as the industry market leader and the name to trust when it comes to condensation and property preservation.

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  Does Cavity Wall Insulation Cause Damp?

  Many properties in the UK have cavity wall insulation and while cavity wall insulation is generally beneficial, poorly installed or defective insulation can contribute to penetrating damp. This can happen if the insulation is incorrectly blown and allows moisture to transfer from the external to the internal wall or where external masonry is defective.

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  Do you clean up after damp repairs?

  Damp treatment may require drilling or removing plaster, which can cause dust and disruption. To get your property back to its original condition, our team uses dust mats, floor coverings and high-spec Hilti dust extraction units to minimise dust and leave your home clean and tidy after installation.

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  Do external damp proof paints really work?

  Damp proof paints create a waterproof barrier that stops moisture penetrating through porous surfaces such as brickwork or stonework. They are effective when installed correctly and other building defects, like missing pointing or spalled brickwork, are dealt with. It is important to make sure to use the correct product, as some seal the surface, thereby trapping moisture, whilst others allow trapped moisture to escape. All products should be installed according to the manufacturer's instructions.

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  When should I use Damp Proof Paint?

  Damp proof paints should only be used after a thorough inspection, and the source of damp has been identified and addressed. If not you could trap damp within a wall which could cause more issues in the future.

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  Can damp walls cause health problems?

  Damp walls and black mould are associated with health issues, as exposure to mould spores over a long period of time can cause issues to the young, elderly or those who are
   Immunosuppressed. Issues like coughing, wheezing or sore throats can also be exacerbated. You should always speak to your GP if you are worried about health implications caused by damp walls or black mould.

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  Can you treat damp without removing plaster?

  This will depend on the type of damp, as condensation and penetrating damp may not require plasterwork to be removed and replaced. Rising damp is caused by ground water often containing hygroscopic salts, migrating upwards through walls. Salts will remain in the brickwork and plaster, meaning over time these could migrate to the surface of the plaster, indicating a damp problem. Hygroscopic salts can pull moisture from the atmosphere, which is known as salt damp. Replastering with a salt retardant additive is necessary to prevent future salt migration.