Damp Walls

Walls becoming damp is a common problem that faces properties in the United Kingdom, especially during periods of high rainfall and persistent bad weather. Damp walls can lead to bad smells, deterioration of plasterwork and can even lead to structural damage to timber.

Damp walls can be caused by various types of damp, from rising and penetrating damp, to condensation problems. Sometimes damp walls are caused by appliances such as washing machines or dishwashers failing, or from internal plumbing problems. Either way, if you notice damp walls it is important to deal with the problem and identify the root cause, this will allow you to then solve the problem.

Rentokil Property Care have put together a guide on how to fully understand what is causing damp walls, and the best way to solve the problem.

Often damp problems can be complex and may require professional help, through a damp and timber survey from a qualified professional. If you are unsure about how to stop the damp problem, you may require a survey to provide answers and recommendations to stop the problem for good.

Damp patches on walls are often caused by moisture penetrating into a building from outside, either from lateral penetration known as penetrating damp, or from ground water rising upwards, known as rising damp. This means that either the design of your property, lack of routine maintenance or even building defects are leading to moisture problems inside.

Damp walls can also be caused by high levels of moisture created from within the property from every day tasks such as cooking and washing, and this is known as condensation. If the moisture vapour in the air cannot escape from the property, it will condense on cold surfaces, such as cold outside walls.

Each type of damp has different indicators, so through a thorough investigation you may be able to identify the root cause of the damp problem. Sometimes damp walls are not caused by a damp problem, but from an internal leak. Pipes and seals on appliances can sometimes cause leaks, while radiators and water pipes hidden within walls may be causing the issue. A common problem is caused by inaccessible shower trays which can overflow or leak from the hidden u-bend. If this is causing the problem you will need to contact a plumber, and will not require damp proofing.

Often the cause of a damp problem inside a property originates from outside. External walls are often affected by penetrating damp, as heavy rainfall alongside building defects can cause moisture to penetrate through masonry walls, leading to damp patches on walls internally. This is particularly true of solid walls, where damp can easily cross from outside to inside.

This is noticeable as brickwork and masonry have dark damp patches, and if left over time moss, algae and other plants may start growing. This can happen if gutters are blocked, so when it rains, water pools around the blockage and once full will pour down the walls. The same can happen at ground level with blocked drains.

Cracks in brickwork and masonry can also allow moisture to penetrate inside a building, causing damp patches. Cracks in renders, poor pointing and even problems with cavity wall insulation can cause damp problems on walls, as this can cause moisture to be trapped or redirected.

If a building lacks a functioning damp proof course, this can cause damp tidemarks on walls, both external and internal. This is often paired with salty deposits. The tidemarks are often accompanied by moss growth on exterior walls suffering from rising damp. Often damp patches on exterior walls will be located in the same position as interior walls, indicating that the problem originates from outside the property.

To prevent a damp problem for good it is essential to understand what is causing it, and solve the issue. If left unaddressed, or if the problem is misdiagnosed, it can lead to further issues in the future, or even more costly repairs - especially if structural timber is affected by timber decay.

Damp problems can sometimes be more complicated than expected, so you may require professional advice to identify the root cause of the problem. A qualified surveyor will use their expertise to diagnose the cause of damp, with specialist equipment used to pinpoint the exact cause and extent of the issue.

If you are worried about a damp problem, a damp and timber survey can provide you with answers, and when required a treatment plan to solve the problem for good.

Rising damp is less common than people expect, because most properties are built with a damp proof course. If a damp proof course becomes defective over time, or if a building never had one to start with, ground water is able to rise upwards through tiny pores in masonry walls. This process is known as capillary action.

When moisture rises upwards it contains dissolved hygroscopic salts from the ground, these get trapped in masonry and plasterwork as the water evaporates. They are also able to pull moisture out of the air into the plaster surface. Over time these salts can deteriorate the surface of walls, while damp patches can form.

Sometimes a perfectly fine damp proof course becomes bridged, meaning that moisture is able to bypass it and allow for the upward movement of moisture into masonry walls. This is often caused by external ground work, raised paths or new driveways. A damp proof course can be bridged internally by plasterwork applied lower than the damp proof course.

The most common sign of a rising damp issue is damp patches that form tidemarks on internal ground floor walls, just above skirting board level. They are often accompanied by salty deposits. Rising damp can cause structural damage to timber, leading to rotten skirting boards, joists and floorboards in the affected area.

If damp patches are high up on ground floor walls, on ceilings or on different stories of a property - they cannot be caused by rising damp -  another form of damp will be causing this problem.

Penetrating damp is the process by which moisture from outside a property is able to penetrate through masonry walls and enter the fabric of a building. When moisture pools around masonry walls it is able to penetrate through and cause damp patches on internal walls. This is especially true if walls are of solid brick construction where there is no cavity barrier to stop moisture penetration.

One of the most common causes of penetrating damp is from building defects because of a lack of regular maintenance. This can be anything from damaged guttering, defective roof tiles and most commonly from blocked and backed up drains. These will often require no damp proofing, just remedial repairs.

High ground levels can allow the lateral penetration of damp into buildings, and will affect properties built into hills or on a slope. This may require more specialist treatments, as masonry is below the ground level. Wind driven rain can cause water to penetrate directly through masonry walls, especially when cracks have appeared or when mortar deteriorates. Again regular maintenance can prevent this, however sometimes porous masonry may require masonry protection cream to create a watertight barrier.

Penetrating damp can affect a property at different levels, meaning floors, ceilings and walls can all be affected.

Damp walls and mould growth are two common symptoms of a condensation problem in a property, and most commonly affects properties during winter or periods of cold weather.

Condensation is caused when there is too much moisture in the air inside a home, and this humid air comes into contact with a cold surface like a mirror, window, or wall. The moisture condenses on the cold surface and leads to condensation forming, and in severe cases beads of water running down surfaces. If left, spores will germinate on these surfaces and mould growth will form. It is common in areas where moisture is produced, such as bathrooms and kitchens, but it can also occur in cold spots in a property, like external walls, uninsulated ceilings or bay windows.

Mould growth is one of the most telling signs of a condensation problem, but mould can also form on occasions due to penetrating damp. This is when the moisture penetrates and causes a cold spot where mould can form.

The most important step before carrying out any DIY fix or treatments for damp is to make sure you correctly identify the type of damp causing the problem, and identify the source. This will mean that any treatments carried out are specifically for the type of damp causing the problem, and the full extent of the issue is dealt with at the root cause.

The treatment processes for damp depends on the type of damp, while other issues may be caused by the problem so a full assessment may be required. It is not uncommon for a damp problem to cause structural damage to walls or timber decay in the form of woodworm, wet rot or dry rot.

If you are unsure about the extent of the problem, or are having trouble identifying the type of damp, a professional damp and timber survey may help provide you with answers.

A CSRT or CSTDB qualified surveyor will be able to provide you with clear answers on what is causing the issue, while providing you with a survey report outlining their findings, backed by evidence. They will also be able to provide you with any recommendations for treatments if required.

The remedial treatments required will depend on whether or not the problem is confirmed to be rising damp, penetrating damp or condensation.

If there is evidence of a rising damp problem, the installation of a remedial damp proof course is the most common and cost effective way to protect walls from rising damp.

This creates a chemical damp proof course which forms a waterproof barrier preventing moisture from rising upwards. It is installed roughly 150mm above ground level horizontally into a mortar course. Often plaster is contaminated with hygroscopic salts that are pulled upwards into the walls by rising moisture, so will need to be replaced. If left it may lead to further salt deterioration over time. Specialist salt retardant plaster is used when replastering to prevent any remaining salts in the masonry from penetrating through the new surface.

Penetrating damp is often caused by building defects, so the first step is to identify the fault that is causing the problem. Sometimes penetrating damp can be solved through minor DIY fixes or repairs carried out by a reputable builder. This can be anything from repairing damaged gutters to repointing external brickwork. For porous brickwork specialist masonry protection creams can be used to create a waterproof barrier from lateral rain penetration. 

Often properties are abutted by high ground levels, in which the internal living environment is lower than the external ground level. This may require elements of waterproofing as the ground level cannot typically be lowered.

It is also quite common to find paved parking areas where the water run-off is directed straight into the house wall, which will cause damp.

Sometimes associated problems such as fungal decay, woodworm and even structural issues like wall tie failure can be caused by penetrating damp. This makes it important to fully understand the extent of the problem, and structural timbers in the vicinity are thoroughly checked.

Condensation and mould problems are caused by an excessive amount of moisture inside a property, with inadequate ventilation. That means for a comfortable internal environment there needs to be a balance between insulation, ventilation and internal heating.

Working extractor fans should be used in bathrooms and kitchens, and some properties may even require PIV units to provide increased air flow throughout the whole property.

Damp patches and mould growth on walls are often caused by cold spots, so thermal improvements to the surface of the wall may be necessary. Specialist thermal plastering systems can be used, while insulation may be required in roof spaces above affected ceilings. For isolated areas anti-condensation paints can be used.

Extensive mould problems in properties may require professional mould cleans, while a damp and timber survey can provide recommendations specifically for the property in question, in order to create a healthy internal environment for occupants.

Damp proof paints are a useful tool for some types of damp, but should only be used when the source of damp causing the problem is confirmed. If incorrectly used or installed it could lead to moisture being trapped inside walls and mask the problem, causing further issues in the future, such as fungal decay.

A professional damp and timber survey should be carried by a professional in order to fully understand the problem, and whether an application of an appropriate damp proof paint is required.

Damp walls and mould growth caused by condensation in isolated areas of a property can benefit from using anti-mould paints. These create a thermal barrier between the cold wall and the warm internal atmosphere, preventing the moisture laden air condensing in this area. Ventilation improvements may still be required, as the air still contains high levels of moisture if not addressed.

Other forms of anti-mould paints contain a fungicide to prevent mould growth, which can be very effective, but the excessive moisture that runs down surfaces caused by condensation must also be addressed. This is typically done through improved ventilation.

For larger walls affected by mould and condensation, thermal plastering is an option.

Masonry protection creams are used on porous masonry walls, affected by lateral rain penetration, often during periods of heavy rainfall. Over time the rain can penetrate through to internal walls and cause damp problems.

The masonry protection cream creates a vapour permeable water-repellent barrier, meaning the walls stay dry. Once applied the cream increases the thermal efficiency of the walls, while preventing internal damp problems. This in turn can help reduce energy consumption and energy bills. While some elements of repointing may be required before being applied, once fully dried the cream will protect against spalling, efflorescence and moss and algae growth.

Yes, damp proof paints do work but should only be applied when the damp causing the problem has been thoroughly investigated and identified. If you do not identify the source of damp causing the problem you may trap moisture within the wall, which can lead to further issues and more costly repairs at a later date.

External damp proof paints will create a waterproof barrier which can stop moisture penetrating through porous surfaces, while anti mould paints can help create a thermal barrier stopping condensation forming on the interior face of cold walls. Often damp proof paints may be required in conjunction with other forms of treatments, hence why it is important to have a professional provide you with recommendations if you are unsure on how to proceed with your damp problem.

Rentokil Property Care are here to help, and have qualified and experienced surveyors local to you.

If you are still concerned about damp walls inside your property and want professional advice, you can arrange a damp and timber survey from a Rentokil Property Care surveyor.

When you have a problem with damp inside your property you want to trust a company to get it right the first time. Our CSTDB and CSRT qualified surveyors will carry out a thorough survey of your property, investigating the root cause and making sure to identify the extent of the problem.

All their findings will be detailed in an easy to understand survey report, with all evidence found detailed within, along with recommendations for remedial treatments, but only if they are required.

Rentokil Property Care has been working in peoples homes and businesses for over 70 years, correctly identifying property issues and providing long term solutions.