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Penetrating Damp

What is Penetrating Damp?

Severe penetrating damp

Penetrating Damp is the process of outside moisture moving from the exterior wall of a building to the interior. It occurs when outside moisture like wind-driven rain impacts against a building’s wall. Building materials such as brick soak up this rain to saturate the wall with Penetrating Damp.

Rain penetration into masonry (penetrating damp) can occur in buildings of all ages. At its most obvious, it penetrates right through the wall and is visible as a damp patch on the internal wall – often causing discolouration and peeling / flaking of paintwork or wallpaper. However, rainwater penetration can be damaging to a property, even if it does not penetrate all the way through a wall. For example, moss growth, increased heat loss, and frost damage can be caused by rain penetration into masonry.

Water soaks through the exterior wall and is absorbed into the substrate, where it travels through to the interior walls. There, moisture manifests as wet spots on the wall. These patches of penetrating damp damage wallpaper, plaster and the walls themselves. This creates a damp environment that causes spores in the air to settle, growing mould and mildew.

Brick and masonry substrates are especially susceptible to penetrating damp. This is due to their interior structure that gives them sponge-like properties of moisture absorption.

Rain penetration is not a problem that is restricted to single-skin walls. Poorly installed wall-ties or cavity wall insulation can provide a pathway for rain penetration to track through cavity walls.

Leaking gutter; a perfect example of a building defect causing penetrating damp problems

In many cases, rain penetration is caused by poorly designed or maintained building details (e.g. blocked downpipes or leaking gutters) causing large amounts of rainwater to flow over a small section of masonry. In these cases, the penetrating damp can usually be cured by rectifying the defect.

Roof damage can let in moisture, causing damp to take hold. Common things to look for on roofs include damaged flashing and pointing, as well as cracked or missing tiles.

The drainage system is also a point of common failure that can lead to penetrating dampness. If exterior drains become clogged, rainwater can collect against the brickwork – leading to hot-spots of penetrating damp. Broken drains can also cause water to fall or collect in irregular areas and cause dampness and mould growth.

Door frames are also common points of ingress for moisture. General damage, cracks and a lack of weather protection devices are the points of failure to watch out for to avoid damp getting in through closed doors.

In other cases, rain penetration can be caused by the masonry wall not being weathertight enough to withstand local weather conditions. Often the weathertightness of the masonry can be improved using external render, cladding, or weatherproof paints. However these solutions all change the visual appearance of the masonry.

Call us on 01403 210204 or submit an enquiry for information on how deal with penetrating damp.

Where does Penetrating Damp come from?

Penetrating Damp (Rain Penetration Through Masonry)

Penetrating Damp usually gets into the home environment through wind-driven rain. When rain falls on a building, it cascades off the roof and runs into the drainage system.

Once it enters the drain pipes, it is safely deposited away from the house, usually through an external pipeline and into the water mains. Foolproof, right?

Wrong. Despite our best wishes, rain doesn’t always fall precisely downwards. The average wind speed in the UK is around 8 knots, or around 9 miles per hour. That’s more than enough to catch falling rain and propel it into your walls.

Wind speed often drives rain at velocity, causing a misting or spraying effect that makes walls very wet, very quickly. In the UK, south-west facing walls are most susceptible to driving rain due to the prevailing winds that travel into the country.

The haphazard nature of wind-driven rain makes it impossible to predict where damp spots will appear. Although wind-driven rain often peppers walls, water ingress will be more extreme in weak spots of a wall.

Some walls may also be more exposed to the elements than others. Buildings that stand alone without protections from rain, frost and wind will suffer from damage to the substrate.

It is important that buildings are regularly maintained and precautionary measures taken. For instance, the application of a breathable masonry waterproofing cream in wind-exposed buildings can decrease this amount of water damage and stop penetrating damp from setting in. Houses and flat blocks on the coastline are also at heightened risk from salty sea spray as well as wind-driven rain.

Penetrating Damp on exterior of a property

The haphazard nature of wind-driven rain makes it impossible to predict where damp spots will appear. Although wind-driven rain often peppers walls,  water ingress will be more extreme in weak spots of a wall. 

Some walls may also be more exposed to the elements than others. Buildings that stand alone without protections from rain, frost and wind will suffer from damage to the substrate. 

It is important that buildings are regularly maintained and precautionary measures taken. For instance, the application of a breathable masonry waterproofing cream in wind-exposed buildings can decrease this amount of water damage and stop penetrating damp from setting in. Houses and flat blocks on the coastline are also at heightened risk from salty sea spray as well as wind-driven rain.

Just as moisture can seep from the outside through to the inside, penetrating damp can too. Leaking appliances like boilers can introduce moisture into walls, where water then travels through brickwork and masonry in the exact same way that rain does. Regular maintenance of boilers, radiators, water heaters, washing machines and taps are essential to keep your home dry.

It is important to remember that Penetrating Damp can affect buildings of all ages at any point in their lifespan. If a building has not been comprehensively damp-proofed with a masonry waterproofing cream, it is susceptible to penetrating damp in wet conditions. Although a damp-proof course will successfully stop rising damp from setting in, penetrating damp from wind-driven rain is still a threat.

How can you identify Penetrating Damp?

Rising damp

Rising Damp

Penetrating Damp

A damp spot is a damp spot. It can be difficult to define exactly which type of damp you have when you notice patches, mould, wallpaper and plaster damage inside the home. The key to correctly identifying penetrating damp is the height at which it manifests. 

Rising Damp comes up from the ground. It will never be found higher than a metre up a structure. If your external damp is at its wettest on the ground and rises to within a metre of the floor, rising damp is very likely. If the damp displays any higher than a metre and its source is not immediately visible on the ground, penetrating damp is the most likely option.

It is also important to consider the conditions around the home suffering from damp. Due to the many possibilities of the culprit behind penetrating damp, it is often more common than rising damp. 

The two conditions can sometimes look similar, and are often mistaken for one another. It is very important that the correct diagnosis is made before attempting to treat your home. If in doubt, the Safeguard Europe Customer Care Team is available to assist with your damp-related problem.

What kind of damage does Penetrating Damp cause?

Corrosion of bricks and mortar

When water-soluble salts like calcium carbonate or sodium sulphate are present inside brick, they dissolve in contact with moisture. The resulting salty water travels through the brick’s capillaries to leach out of its surface. Moisture evaporates on the wall, leaving a white and powdery substance on the surface. While efflorescence itself is mostly an aesthetic problem, it is a warning sign of dampness within a wall. 

If you’ve discovered efflorescence on your walls, penetrating damp may have taken hold. Water saturation damages bricks and mortar. Excess moisture pushes pressure outwards, which causes a type of damage called spalling. This refers to the flaking and crumbling that occurs on the brick’s surface. 

In extreme cases, spalling can lead to structural instability. Parts of the brick and mortar fall away and become weak points in the structure. Once this kind of damage has set in, penetrating damp will only get worse. Spalled bricks and mortar let in even more moisture, causing further deterioration at a quicker rate.

Woman inspecting wall covered in black mould

Damp brickwork and masonry encourages black mould growth on walls. Although black mould is more common internally due to the higher temperatures needed for growth, it can grow on exterior walls too. Black mould thrives in wet, warm and humid conditions. The combination of cold weather, warm interior heating and wet walls means that black mould is always present in structures with a penetrating damp problem.

Black mould is harmful to the health of buildings and people. It can be difficult to get rid of, requiring the removal of the visible mould as well as the invisible hyphae that exists below the substrate. Treatments like the Dryzone® Mould Removal & Prevention Kit can be used to eliminate mould and prevent its recurrence for up to 6 months after application. But that isn’t the only growth that homes suffering from penetrating damp must reckon with.

Green algae on an old brick wall

Sunlight, minerals and water make up the recipe for algae growth. Damp exterior walls have all 3 in abundance. Although algae looks fragile, those spidery green spores are actually incredibly resilient. Their roots burrow deep into brickwork, taking hold within walls. 

Algae roots produce acids that unbalance the alkalinity of bricks and damage them. It also damages mortar joints in much the same way.

Inside the home, penetrating damp can wreak havoc on plaster and plasterboard. Both types of interior finish are porous, capable of absorbing lots of moisture. Plasterboard can swell and soften, while plaster can blister and flake. This damage is both unsightly and structural, weakening and damaging the finish of the wall while providing the perfect conditions for mould to grow.

Where wooden fixtures, furniture and skirting boards directly contact the damp wall, the moisture transfers through. Where fungal spores are present, this can cause wet rot. Penetrating damp can cause serious damage if it reaches structural timber and will need immediate professional attention.

Cavity Walls vs Solid Walls

Solid Wall Internal insulation with plasterboard, stormdry and Dryrod installed

Insulated Solid Wall with Stormdry application and Dryrod DPC

Insulated Cavity Wall with Stormdry Masonry Cream applied

Cavity walls are common in modern house construction. This refers to how the walls are constructed, and they are usually built this way to facilitate cavity wall insulation. Very simply, a cavity wall is a wall formed of two separate layers of wall – one inside, one outside. The gap in between is where the wall insulation goes. 

A modern cavity wall specification will usually include weep holes, which are intended to provide a path for moisture which gets into the wall to exit it. These holes are connected to cavity trays inside the wall, which collects and diverts the moisture that penetrates the wall. With the moisture safely diverted out of the wall, penetrating damp cannot soak through to the interior wall. Assuming the weep holes and cavity trays have been placed and installed correctly, this type of construction is effective at keeping out penetrating damp. 

However, in properties that date earlier than the 1920’s, solid walls are the most common type of housing construction. Exactly as it sounds, solid wall construction means that there is a single unbroken wall dividing the interior from the exterior. As brick and wood are porous materials, solid wall constructions are much more vulnerable to penetrating damp than cavity walls.

How to prevent Penetrating Damp

The best way to ensure penetrating damp does not damage your property is to take preventative measures before the damage begins. Regular maintenance of guttering, downpipes, roofs and windows will also ensure help to defend the home from damp before it sets in. Checking renders and sealants regularly for early signs of damage will also ensure that moisture does not find its way into the wall.

Regular home maintenance also has an important part to play in treating penetrating damp. Plumbing and central heating are common causes of penetrating damp within the home. Boilers must be serviced annually and a simple plumbing check must be regularly undertaken to ensure that pipes are not corroded or leaking. Small leaks have been known to drip onto adjoining walls for a long time before anyone notices.

The application of a breathable waterproofing masonry cream like Stormdry Masonry Cream on the outer walls is recommended to build an effective hydrophobic barrier from moisture ingress.

Breathable Colourless Water Repellents for Masonry

Stormdry soaking into a wall over 24 hours

Brick wall absorbing Stormdry over a period of 24 hours

Breathable, colourless [1] water-repellents offer a solution in situations where there is a desire to maintain the visual appearance of the masonry. They work by lining the pores in the masonry rather than blocking them. This allows the wall to breathe naturally and allows any moisture present in the masonry substrate to escape.

Since 1983 Safeguard have been producing breathable, colourless water-repellents based on active silanes and siloxanes. These molecules form an extremely strong and stable bond with silicaceous building materials such as brick, mortar, concrete, and sandstone. In the case of our deeply-penetrating Stormdry Masonry Protection Cream this results in a life expectancy of 20 – 30 years.

Faulty mortar must be repointed

It should be noted that products of this type are only intended to block rain penetration through the pores of the masonry. Cracks in masonry will have to be filled or repaired. Faulty mortar should be re-pointed using a suitable sand/cement or sand/lime mix incorporating Stormdry Repointing Additive. This additive contains silane and siloxane water-repellents as well as additives to promote bonding and reduce shrinkage. In cases of wind-driven rain, even mortar beds that appear to be in good condition may need to be re-pointed as wind-driven rain is able to permeate through tiny shrinkage cracks between the mortar and the brick / stone. Please contact our technical department on 01403 210204 or submit an enquiry for further information.

[1] These products may cause some slight darkening to certain substrates. Although this will usually fade over time, a small, representative and inconspicuous test area should always be treated before full treatment begins.

How to treat Penetrating Damp

Treatments for Penetrating Damp

The most important factor in treating a penetrating damp problem is to ensure that walls no longer allow moisture and water ingress. Black mould can be treated inside the home with biocidal sprays like Dryzone Mould Removal and Prevention Kit, but unless the root cause of penetrating damp is fixed, it will reoccur. In cases of external algae, lichen and moss growth, treatment and removal must be carried out before further damp treatments are carried out.

Spalled brick and mortar must be fixed and repointed to avoid extreme water ingress. Waterproof repair mortars like Drybase Universal Mortar are effective ways to spot-fix damaged substrates, while repointing additives like the Stormdry Repointing Additive range can heal and prevent further damage to mortar joints.

Saturated plaster must be stripped and replaced. Damp-proof replastering options are available to prevent plastering damage should dampness reoccur. Options include –

Damp plasterboard must be assessed for damage and mould growth, dried out if possible or replaced entirely. 

In cases of penetrating damp through roofs, damaged roof tiles must be repaired or replaced. Chipped or cracked flashing or pointing must also be repaired. Underneath the tiling in many modern roofs are EPMD rubber membranes. These can disintegrate in places, and where they fail, they will allow moisture in through the roof.

Door rain deflectors and door draft seals are two possible additions that can stop rising damp around doors. In these cases, exterior silicone seals around door frames must be checked and repaired.

Some types of paint or waterproofing coating do not allow for vapour permeability. It is very important for houses to be able to breathe in order to maintain healthy humidity levels. Damp which penetrates through structures that cannot breathe will remain wet, as the moisture cannot escape the coating. Breathable waterproofing creams like Stormdry Masonry Cream ensure that moisture leaves the wall while maintaining a completely hydrophobic surface.

  1. Ensure that all leaks from water-retaining appliances like boilers and radiators have been contained and fixed. 
  2. Plumbing is also a major source of non weather-related damp. 
  3. All standing water must be drained out of the wall & damaged areas must be dried and repaired. 
  4. Dehumidifiers can help to dry out damp rooms once the core problem has been rectified. 

Book our free Penetrating Damp CPD Webinar

Be aware – walls can take months or even years to fully dry out. Reducing the humidity of your home and being aware of the causes of condensation will help you maintain a dry home. Check out our condensation guide.

Safeguard Europe has been battling penetrating damp since 1983. As well as an extensive range of damp-proofing products, we also have years of experience to share. Our Continuing Professional Development Webinars are approved by the Royal Institute of British Architects. Hosted by Certified Surveyors in Structural Waterproofing, Research & Development scientists and experts, get yourself fully trained up with the latest in damp-proofing methods and materials.

In our 1 hour Penetrating Damp Webinar, you’ll find out:

  • Why penetrating damp is a problem
  • The causes of penetrating damp
  • The process of rain penetration through cavity walls
  • The four-step process for treatment of penetrating damp
  • Primary and secondary protection against penetrating damp

Alongside Penetrating Damp, we also offer a wide range of other building industry webinars. Discover out how to deal with condensation or learn more about dampness in buildings with Safeguard Europe.

For more information call
01403 210204