If left untreated, damp can damage much more than a building’s appearance. It can lead to the deterioration of plaster and masonry, promote timber decay and create unhealthy conditions for occupants. Unfortunately for property owners, inappropriate treatments for damp commonly cause greater harm to structures than years of degradation. We explain how you to can prevent and remove damp from your home with the correct damp treatments.
Rogue damp proofing contractors or misunderstanding electrical moisture meters can frequently lead to unnecessary expense and damage through the retrospective installation in walls of horizontal damp proof barriers (damp proof courses or DPCs). Equally the harm done by modern solutions that aim to seal old walls rather than improve their ability to breathe is underestimated. An appreciation of how the basic construction of older buildings differs from that of new ones will help you avoid such misguided remedies.
Older buildings such as Victorian, Edwardian, 1930’s and those of traditional construction methods such as Cob, Lime and Wattle and Daub must be allowed to breathe. Whereas modern buildings rely on keeping water out with a system of barriers, buildings that pre-date the mid-19th century are usually constructed of absorbent materials that allow any moisture that enters to evaporate back out.
Because most old buildings were constructed with solid walls without DPCs and originally had no roofing felt, rain or below ground moisture could both enter. This did not, however, mean dampness was inevitable. Before central heating was commonplace, heat from open fires drew in large quantities of air through loosely fitting windows and doors. This high rate of ventilation would have quickly evaporated moisture from permeable internal surfaces while the wind dried out any damp roof timbers or permeable external wall surfaces.
An equilibrium was therefore established whereby the moisture being absorbed was equal to that evaporating. When upgrading an old building, you must maintain this equilibrium for the building to work as intended and remain dry.
Main causes of dampness
The main risks arise from:
Condensation: Energy-saving measures that reduce ventilation in old buildings such as double-glazing increase relative humidity. Humidity is also raised by modern lifestyles that generate large quantities of water vapour, from bathing, cooking and washing. Condensation will occur on any surface below the dew point (i.e. temperature at which saturated air releases surplus moisture vapour). Interstitial condensation within the pores of materials reduces thermal insulation and further increases the risk of condensation.
Penetrating damp: Roofs, chimneys, parapets and other exposed parts of a building are most susceptible to rain penetration, especially where access for maintenance is difficult. Junctions in roofs are potential trouble spots, with water exploiting defective lead flashings, mortar fillets, ridges or hips. Concentrated and prolonged wetting of walls and external joinery arises from poorly maintained rainwater fittings, and leaks from parapet and valley gutters can cause significant damage to structural roof timbers. Hairline cracks in pointing and render invariably admit moisture where cement mortar has been used for repair, rather than lime.
Internal leaks: This results from overflowing baths or showers, burst pipes, the gradual breakdown of pipe joints, leaks from washing machines or dishwashers, and accidental damage.
Below ground damp: This may be rising damp, which is neither as widespread as commonly thought nor a total myth, as sometimes now claimed. Floors become damp where the evaporation of moisture from below is inhibited by vinyl sheet, rubber-backed carpets or other impervious coverings. New concrete floors or impervious coverings also drive excess moisture into the bases of nearby walls (including chimney stacks), where it rises by capillary action. DPCs were not compulsory in walls prior to 1875 but this is only likely to become a problem where breathability is compromised. In addition to rising damp, below ground moisture can result in problems where ground levels around your building rise unduly.
Bridging damp – Can be commonplace brought about innocently by raising external ground levels such as raised flower beds against bays or laying new drives over the top of existing ones. This allows rainwater to ingress to the decorated side of a property by means of bridging across a cavity by means of building debris within it.
Tips for Diagnosing Damp
Roofs and Rainwater Fittings
Inspect your roof during wet and windy weather to decide if a damp ceiling patch is due to roof leakage and/or condensation. Debris on the ground (broken slates, tiles and so on) or daylight seen inside lofts indicate possible roof problems.
Defective rainwater fittings may be most obvious during heavy rain, but stains on walls and plant growth provide further clues. Don’t forget to check gulley’s at ground level.
Condensation typically occurs between October to April, basically when external temperatures drop leading to us keeping windows and doors shut subsequently reducing the volume of fresh air getting into properties to maintain internal humidity levels at between 40 – 60%. It normally appears as beads of water droplets on hard shiny surfaces such as windows and window frames and as mould growth on internal finishes. It is intermittent, like penetrating damp, but unrelated to wet weather.
Penetrating damp typically shows up as well-defined patches after heavy rain typically to south westerly facing walls. Anticipate moisture ingress through hairline cracks in unsuitable hard, modern cement pointing or rendering.
Below ground moisture causing rising damp can extend up to 900mm above floor level, sometimes with a classic tidemark on finishes. Salts appear as white deposits and if internal humidity levels are high, mould growth can form over the top of this damp.
Water leaks from radiator pumps, sink and bath plumbing, shower trays, sealant around bath’s and showers, etc can be very damaging if left undetected or ignored.
Damp Proof Course and Alternative Systems Compared
Inserted by cutting in or during rebuilding. Can cure rising damp but this drastic method is usually inappropriate. The drawbacks to this practice are possible major structural problems, potential damage to historic finishes internally, unsuitable for randomly coursed walls, access difficulties and ongoing deterioration sometimes of masonry below DPC where moisture is concentrated. It is also very labour intensive making it the most expensive practice.
Walls impregnated with a chemical solution through holes at bottom to create a new chemical damp proof course. Widely used today but not always appropriate for period or listed buildings. Can be supported by 20-year insurance guarantees if installed by approved contractors.
Drawbacks: drilling holes inadvisable in flint, granite, etc. Hard to form proper barrier in rubble walls with voids, drill holes are unsightly and incorrect application can result in little or no improvement.
Holes drilled to receive porous siphons approximately 50mm in diameter that absorb damp and evaporate it from each tube. Sound in theory but problems may occur in practice. Drawbacks: salt accumulation in tubes may increase moisture; air-flow sometimes inadequate; tubes commonly set in hard cement mortar; unsightly.
A system that dates back centuries. Electrical potential aimed at reducing capillary rise of moisture in the ground by using electrodes bedded in wall.
Suitable only in solid walls, very thick walls and very commonly used retrospectively in Spain and France. Can be very effective but relies on an unbroken, un-disrupted small electrical current. Not expensive to run but if not maintained as an ongoing supply can result in damp rising from the ground.
Drawbacks: Requires installation ideally by a specialist. Cannot have the circuit broken by way of alterations to the property or loss of power supply.
Qualified surveyors have a legal duty to follow a process of diagnosis arriving at rising damp being the last reason for damp in so much as it can be a very invasive, messy and expensive remedial process potentially leading to undue stress to a structure. Regrettably, many still simply note the occurrence of high meter readings and pass on all responsibility for further investigation to remedial treatment contractors. These contractors have a vested commercial interest, encouraging over-specification. Should a mortgage company insist on work you believe is misguided, challenge this and consider obtaining a written report from an independent surveyor or architect.
Effective remedial measures depend on accurate diagnosis, but applying staged remedies can also be part of understanding the cause of a damp problem. Quite often, the first remedy may involve nothing more than basic maintenance such as clearing a blocked rainwater gulley. Remedies will either cure dampness by addressing the cause (for example, improving drainage) or will manage it by treating the symptoms (changing washing or cooking habits, for instance).
Be sceptical of contractor guarantees. They amount to very little and legal backing or commitment. The only remedial damp proofing guarantee of any tangible value is an insurance backed guarantee.
Controlling Air Moisture Condensation
Condensation can be treated by reducing air humidity or keeping surfaces above dew point temperature. Humidity is reduced by cutting the amount of moisture available or increasing ventilation by opening windows, etc. Tumble dryers should be vented to the outside if not of the condenser type, and clothes drying indoors is best avoided.
Temperatures are maintained above dew point with suitable heating. The permanent use of dehumidifiers is NOT a permanent solution to condensation.
Condensation in chimney flues can be eliminated with proper linings. Redundant flues that have been sealed should be fitted with ventilation grilles or re-opened. Lofts should be well insulated and ventilated but make sure insulation does not restrict ventilation at the eaves.
Controlling Penetrating Damp
Reinstate dislodged and missing slates and tiles before damage occurs to roof timbers or plaster ceilings. SPAB, the Society for the Protection of Ancient Buildings, recommend that renovators avoid spray-on roof foams for the underside of roofs, or external bitumen coatings although other experts disagree. SPABs view is that they prevent proper inspection, hinder the re-use of slates or tiles and, by reducing ventilation, increase the risk of decay.
Brush moss off roofs since it can block gutters and retain moisture, which may damage certain roof coverings in frosty weather. Also, clear gutters and rainwater pipes regularly, particularly if your building is surrounded by trees or perched on by pigeons.
Re-point deeply eroded mortar joints in walls. Whilst sand and cement with a plasticiser is fine for modern buildings, it is important to use a lime based material (preferably without cement) for most buildings pre-dating about 1900. Localised re-pointing is generally all that is required.
Where rain penetrates exposed south west facing walls, limewash, lime render and slate or tile hanging are traditional solutions although these cannot be employed without changing the external appearance of the wall. The use of high grade, colourless water-repellent treatments do a good job to protect the brick face and mortar of exposed elevations. You should carry out a trial area before applying to all walls.
Controlling Below Ground Damp
Once correctly diagnosed a failed damp proof course will need to be replaced. The most cost effective solution for this is a chemically injected DPC. To be effective this must be applied in the correct position and in the right volume.
Before this kind of work is undertaken firstly, tackle all other potential issues such as raised ground levels, damaged render or plinths, localised flooding around the property or affected wall, poor drainage and allow the wall to breathe and dry down naturally.
Brick/masonry can take as much as one month per in the thickness of the wall to fully dry down.
Reducing or removing the source of moisture may also help alleviate rising damp. French drains can be an effective and relatively inexpensive answer but it is preferable not to site them directly against walls and rodding points must be provided. Otherwise, blockages can effectively convert them into a sump and increase dampness. Consider also the structural and archaeological implications.
In respect of an old or period building always consult with the appropriate bodies before applying any treatments to get their recommendations for a preferred remedial strategy.
Similarly, the eradication of any contributing moisture from other sources such as rain splash from raised Drives and Patios could prevent the need for more extensive remedial treatment.
If damp issues have been present but the internal plaster and decorative finish is sound there is not always a need to remove the plaster. It may dry down fully of its own accord. If, however salts or staining are present, we recommend that as part of a standard procedure for new chemical damp proof treatments that the plaster is replaced to a minimum of 1 meter from the floor or to 300mm above the highest point of recorded damp.
Why use Alliance?
Set up with one purpose in mind and that was to keep things simple!
This means that we can operate a no-frills business that allows us to pass our negotiated supplier discounts onto our customers. As suppliers to the Landlords National Property Group as well as programmes like Restoration Man and Amazing Spaces you know that you are getting the best possible quality.
A reason why many customers continue to return time and time again and not just for the discounts and the low prices. Here at Alliance Remedial, we can supply top quality specialist products so you can be sure that you are getting the best service.
If you would like to know more about our damp proofing, ventilation and other products and services contact us today and we will be happy to find the ideal solutions to help keep your property damp free and comfortable!