Remedial Timber and Damp Heritage Specialists
Wall Stabilisation Specialists

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Damp Proofing

Rising Damp

Rising Damp can be defined as “moisture that is soaking up (typically) a wall or floor from below ground, i.e. finished external ground level, or internal oversite level”, Ralph Burkinshaw and Michael J Parrett, ‘Diagnosing Damp’, RICS. The legal requirement for a damp course was introduced in 1875 so if your house is younger then it most probable has a DPC. Slate, engineering brick or bitumen mixed with mortar were in earlier damp courses. Bitumen felt damp courses are the most common type and were used mainly between the 1920’s and 1980’s. Plastic strip damp courses were used from the 1970’s and are now the most common type of damp course in new construction.

Rising Damp is rarely due to a ‘failed DPC’ or a ‘broken down’ DPC. Common causes may be due to not having a damp course in the wall, or by debris bridging the existing damp proof course. Another common cause is high ground levels. Moisture from the ground damp contain hygroscopic salts and as dampness evaporates from the surface of the wall, the salts remain in the plaster. These salts build up and absorb moisture from the air making the problem even worse.

We will never recommend the application of dense cement renders as this is inappropriate, unnecessary and causes irreversible damage to the walls it is applied to. So called ‘rising damp’ control systems serve only to mask problems. Where necessary, our approach is to deal with the cause of the problem and if it is deemed necessary, to line the walls with a ventilated plaster lathe which we can plaster with lime mortar or light-weight plaster.


When warm, moist air comes into contact with cooler surfaces, the excess moisture in the air condenses. That’s because the cooled air next to the cool surface can’t hold as much moisture as the warmer surrounding air. In other words, as moisture-laden air gets close to the cold surface it starts to get cooled and so the relative humidity increases; the greater it is cooled the higher the relative humidity and the more it reaches saturation.

Years ago, before energy efficiency became a concern, homes were not built to be weathertight. Insulation concepts were very basic. Walls and ceilings were made from much more porous materials. Thus, water vapour could easily flow in and out of walls. Today’s homes are much less ‘permeable’ (they don’t let moisture escape through the walls). Windows and doors are built to reduce air leakage, and weatherstripping, modern insulation, vapour barriers and new construction techniques can help keep cold air out and lock moisture inside. As a result, moisture created by bathrooms, kitchens, laundries, plants and occupants can result in higher interior relative humidity. In the worst conditions this can build up to excessive, even harmful, moisture levels.

If materials in the property become badly affected by condensation they can become damp and mould can begin to grow. The mould that usually grows in these conditions is the black spot mould (Aspergillus Niger).

Resolving major condensation problems involves correcting the temperature, humidity and ventilation of the property. We can fit a full home ventilation system that will reduce the condensation in your home, alternative we can fit additional air vents.

Penetrating Damp

Penetrating damp is classed as any water that finds its way inside from the outside. It occurs at all levels of the building but is more prevalent higher up and on south west facing walls. Overflowing gutters, missing roof tiles, downspouts, leaking pipes, badly fitting windows or doors and damaged pointing, cladding, flashing or render are all sources of penetrating damp.

In the UK, one of the primary causes of penetrating damp these days is poorly installed cavity wall insulation. Cavity walls were actually developed to prevent water from penetrating the inner structure, serving as a kind of weather shield. However, when insulation is introduced, a bridge is created between the outer and inner walls, allowing the water access to the interior of the building.

The best way to address penetrating rain is to eliminate the cause. This can be as simple as clearing gutters of debris, repairing a crack, or replacing roof tiles. If the cause cannot be eliminated, there are solutions such as colourless, breathable water repellents that provide protection without changing the appearance of the brick or masonry, and ventilated dry lining systems.

Damp Proofing - Diagnosis Chart (for guidance only)


Time and Weather

Cause -> Treatment

Patches on external walls usually on lower exposed elevation.

After rain

Cause: Penetrating Damp, (porous masonry)

Treatment: Re-pointing, Exterior water repellent/render, bridged cavity

As above, also upper elevations, but related to external defects (pointing, chimneys, flashing, windows, rainwater goods etc.).

After rain

Cause: Penetrating Damp (external faults)

Treatment: Various structural repairs

Running water or damp patches below ground level.

Dependent on water table or rainwater saturation of soil

Cause: Penetrating Damp (basement)

Treatment: Various 'tanking systems'

Patches or continuous bands in ground floor rooms extending up from floor level.

Usually persistent, prolonged damp

Cause: Rising Damp from bridged cavity, concrete floors, wet insulation in walls, high ground level

Treatment: Identify and remedy the cause

Damp patches showing on plaster as an after-effect of rising damp. Occasionally, damp patches on chimney breast.

Before and possibly during rain (typically 'comes and goes')

Cause: Hygroscopic damp (salts)

Treatment: Ventilated Plaster Lath system

Patches on external walls, often in corners, within cupboards. Moulds disfiguring surface. Especially prevalent in or near kitchens and bathrooms.

Usually in cold weather

Cause: Condensation

Treatment: Improve ventilation, and/or heating (or insulate). Consider mould control system where other measures not feasible