Stop Damp and Condensation

Penetrating Damp

Water permeates the structure of the building, only during wet weather, drying out when the weather improves. More serious cases may mean the wall itself has become porous – more common in older, solid wall structures, it will more than likely require re-pointing and any spalled, crumbling or frosted brick faces making good if not removing and replacing with new ones before any further treatment is applied.

Cause and Effect

Rising  and penetrating  damp describes the movement of moisture within a structure upward or through permeable building materials by capillary action, suction and absorption. This moisture will dissolve soluble salts from the building materials such as calcium sulphate, and may also carry soluble salts from its source.

If the moisture evaporates through a permeable surface, these salts will be left behind and form deposits on or within the  surface. Where there is a large permeable surface, salt crystals are deposited as a harmless flour-like dusting on the surface.

If evaporation is restricted to localised areas such as defects in an impermeable paint finish, then salt deposition is concentrated, forming thick crystalline deposits with the appearance of small flowers; hence the term ‘efflorescence’.

When evaporation occurs within the material, salts can be deposited within the pores. The expanding salt crystals in these locations may result in fractures forming in the material and degradation of the surface. This type of decay may be seen in porous brickwork or masonry and particularly where bricks have been painted with impermeable/oil based paints.

When there has been a long-term problem with moisture penetration, evaporation at the edge of the damp area leads to a distinctive ‘tide mark’ as a result of salt deposition. Where this occurs at the base of a wall, the tide mark is often taken as a typical diagnostic feature of ‘rising damp’.

However, these salt accumulations may remain even when the water penetration that originally caused them has long gone. Similarly, water penetration may have occurred from causes other than ‘rising damp’.

The accumulation of ‘moisture reservoirs’ in the foundations may also arise as the result of chronic plumbing leaks or floods from plumbing, drainage defects, sub terranean ground movement and climatic changes resulting in higher and lower water tables.

Damp conditions in walls can be caused by chronic condensation problems and as a result of saturation and gravity particularly badly at the foot of the wall thus masking and exacerbating a rising damp problem . We find there are many condensation problem’s caused through poor wall insulation , none breathable wall coatings and inappropriate use of water repellents and cement additives.

Condensation

This occurs when warm moisture-laden air cools to due point (the temperature at which moisture condenses) against a cold surface. Such cold surfaces commonly occur when the insulation value of the external wall is reduced by water penetration, as described above.

Intermittent occupancy of the home with intermittent heating provides the conditions for condensation, inducing unwanted moisture on cold damp surfaces, particularly in ground floor bedrooms. These phenomena are the main causes of damp in the base of walls rather than ‘rising damp’ alone.

Damp and saturated masonry at the base of walls may lead to a number of more catastrophic problems over the long term.

Managing damp

There are many reasons why walls suffer from high moisture levels in the base of walls other than ‘rising damp’, and even when it is a significant factor. The resolution of problems due to high moisture levels requires the proper identification and diagnosis before a cost-effective and appropriate solution to the problem can be found.

Damp Courses (DPC’s) and Damp Proof Membranes (DPM’s)

These are basically mechanical barriers designed to repel damp not cure it. An appropriate moisture barrier must be chosen carefully save not to drive damp in different directions and cause problems elsewhere in the structure. The effect of inserting a damp-proof material into a structure can lead to the appearance of fresh ‘rising damp’ in other walls for example following the laying of a new concrete floor with a damp-proof membrane.

This is most often done when a suspended floor structure is replaced by a solid floor, or when a breathable stone slab floor is lifted and re-laid. Before the alteration to the original floor, moisture would have been able to evaporate off a large surface and be absorbed into the substrate even if this may be soil, without affecting internal finishes. However, a new impermeable membrane allows the water to accumulate beneath, forcing it to the sides of the room and into the base of the walls and through Capillary Action up the walls into the superstructure if no DPC is apparent in the walls.

DPC’s and DPM’s do not provide the complete solution to chronic damp problems. Adequate Ventilation is also a major component of any damp eradication and control scheme.

‘Chemical damp-proofing’ may provide a useful barrier to damp in the short to medium term where the walls are of uniform construction such as sound brickwork laid with strong cement mortar, especially if they are combined with a ventilated dry lining systems or other building detail which allows moisture to dissipate.

This method is most unreliable where walls are of natural stone, because the injected chemical will follow the lines of least resistance and may not accumulate in sufficient quantities where it is needed and thus must be saturated to ensure proper protection and to overcome high porosity levels of the stone type for example sandstone versus granite. Chemical treatment of stone is not always the best time tested solution for controlling and curing damp problems.

This is particularly prevalent when the wall is made up of materials of differing permeability, as is common in the thicker walls of older buildings where the bricks and mortar may be of variable consistency and the structure may include cavities, particularly when the wall consists of brickwork or masonry skins containing a rubble/random infill.

Rendering down to ground level is a very common source of moister and where a DPC is present can ‘bridge’ the intended barrier allowing water through capillary action to rise above the barrier and into the super structure having the effect of sucking the moisture out of the ground .

Breathable Wall Surfaces

The use of traditional lime mortar renders and more modern polymer modified cement based rendering systems allow walls to breathe more easily.

Correct detailing of renders designed to shed water clear of the base of the wall and to prevent ‘bridging’ of any existing damp-proof course is therefore essential. Insertion of an appropriate bell cast bead (flared bead shaped like a bell) allows the render to kick out slightly thus enabling water to be shed away from the wall surface and percolate down to the footing/foundation level.

Waterproofing the surface off the brickwork below DPC level also helps to repel excessive surface water until natural drainage occurs and reduces the pace at which ground and foundation level brickwork deteriorates.

Wall Cavity

An intended airspace incorporated in the design of the building to improve insulation and protect from damp and weather and water ingress, contrary to popular belief cavities have been used over the centuries and there are many examples like, the construction of old brick built Methodist Chapels going back several hundred years such as the one featured in our web site.

Cavities are created by two separate leaves of walls tied together for added strength and stability. This is not always done too securely with header bricks or more recently mechanical ties and fixings. Cavities are often compromised by debris accumulating during the construction and build process or by the ill-advised injection of some proprietary branded insulation foams.

These defects may also bridge existing damp-proof courses, allowing water to penetrate to interior finishes. In some cases, the most cost effective solution is to reinstate a through-ventilated cavity, install better quality fill materials or externally insulate and render the walls.

Generally, failures in existing damp-proof courses are the result of bridging by inappropriate repairs and alterations, by raised ground levels or by localised damage due to structural movement or poor building work. If a damp-proof course is an original design detail created to control moisture movement in the structure, it may be necessary to carry out local repairs. This is best done by ‘cutting in’ a new layer of damp-proof material locally rather than by the general injection of hydrophobic solutions into the masonry to create a ‘moisture movement restricting barrier’ or injected damp proof course as most people know it.

Ventilation

Traditional buildings built in damp or potentially damp sites commonly included through-ventilated sub-floor cavities, cellars or basements. These act as sumps to allow the evaporation and dissipation of moisture from the structure before it reaches occupied areas or vulnerable finishes. Indeed, in some parts of the country it is not uncommon to find streams running through the cellars or basements in old farmhouses. These were often retained as a source of water for domestic use. However, if the ventilation of a basement, cellar or sub-floor cavity has been restricted, moisture can build up and penetrate vulnerable structures.

This can occur, for example, by earth and plants clogging air bricks or by the ill-advised application of relatively impermeable materials. The solution to these problems if they develop, is to re-establish ventilation, before applying further damp-proof materials.

As described earlier, the reinstatement of a through-ventilated suspended floor is generally preferable to its replacement with a concrete slab. The requirement for the continued dissipation of moisture does not preclude the use of basements and cellars as occupied areas, but means that walls should be kept ventilated and not sealed.

This can be achieved by using through-ventilated dry lining systems rather than impermeable finishes or tanking materials, which would only force moisture into adjacent structures above or to the side.

Traditionally, dry lining has been produced by the use of timber panelling spaced from the masonry with battens or the use of lath and plaster. In all cases, the cavity behind should be ventilated at the top and at the bottom to allow through-ventilation to dissipate moisture, as otherwise moisture will accumulate to cause damp and decay problems.

This commonly happens when insulation material or debris is allowed to block the cavity behind lath and plaster or when impermeable paint layers accumulate over timber panelling. These defects are easily solved and the traditional ‘farmhouse’ technique of timber panelling to dado level can be an attractive and cost-effective solution to problems of damp penetration or condensation affecting the foot of masonry walls.

Modern materials and techniques may be used to achieve the same end, and many products are available on the market to allow the cost-effective provision of through-ventilated dry lining systems, including specialist plasterboard systems and plastic ‘Platon’ membranes.

Even with the loss of traditional skills and the complexities introduced into building by new materials and new styles of occupancy, the conditions resulting in damp to the base of walls can easily be avoided with a little thought and scientific understanding. Indeed, new materials and techniques can often be used to advantage if their properties are analysed as potential environmental controls. In contrast, the miss-diagnosis of rising damp and the general application of particular products and techniques without considering the consequences leads to the unnecessary waste of money.

Weather proof coating is a good idea providing the natural properties of the bricks is maintained in particular surface appearance and breath- ability. Bricks and mortar must be allowed to breathe naturally. If rendering is undesirable especially if the building is of historical interest, like many period buildings and those listed under local planning and preservation laws. Gutters, down pipes and poor roofing are a constant source of damp and water ingress to these buildings because they are usually old and leaky, check to make sure they are not overflowing.

A more rational approach to the diagnosis and treatment of damp problems in buildings is simply about using common sense  and reinstating established building practice and appointing a specialist you know you can trust.