The Problem
Condensation is by far the most common cause of dampness in buildings, probably accounting for most dampness problems reported. It affects both old and new properties. Condensation is directly associated with mould growth, and it is this that the occupier first sees and gives an idea as to the potential scale of the problem. The mould is usually found on decorative surfaces, especially wallpapers, where it can cause severe and permanent spoiling.
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So what to do? Well, first thing. Is there a working extractor fan in the bathroom? Is it used every time the bathroom is used? Ideally, a unit which activates every time the bathroom light is switched on is needed. Better still, a fan which continues to run for five minutes after each operation – even when the light is switched off.
If there is a fan, is it ducted out of the building properly? If it’s in the ceiling or not on an outside wall, there must be ducting leading to an external vent – check it. The fan is useless without it. When the fan is operating, can you put a sheet of A4 paper over the grill and leave it hanging by the suction? If not, then the fan is either defective or is not powerful enough (this can be caused by too many bends in ducting too).
Next – repeat for the kitchen. A cooker hood may look nice and have the latest in ‘carbon filtration’ but this will not remove moisture from air. Check that any cooker hood has a ducting kit, leading to an outside grill. Without a duct it is useless. It must be used when cooking, boiling a kettle or washing pots. If there’s no hood, then install an extractor fan – minimum 150mm diameter and it must be diligently used.
Extractors work just like an open fire would. They expel air, with the moisture and such in it. This is replaced by dryer air, which is drawn in via small gaps and ventilation grills, such as the very small ones over windows. If you can find these ‘trickle vents’, then do check
they are open and leave them open.
Taking into account the differences in lifestyle and housing which has happened over the last 50 years or so – the extractors in bathrooms and kitchens are the most undervalued essential components of a modern house. If they wear out, break or are neglected, condensation problems will almost always follow.
The next thing is keeping an eye on moisture production. Okay, we still have to dry clothes, but remember how heavy those clothes were, fresh from the washing machine? And how light they are when they’ve spent a few hours on the clothes rack or radiator? All that weight loss
is water, which is now in the air. So it is sensible to try to limit that. This can be done by using one room as the drying room, rather than having wet clothes willy-nilly, all over the house. The drying room can be gently heated and the window opened to let the warm moist air get out – remember to keep the internal door to that room closed, so that the warm moist air doesn’t spread around the house and cause more condensation. If you can, try to avoid drying clothes this way (apart from a tea towel and bath towel in the kitchen and bathroom of course).
If the above is in place and there are still issues, then that’s the time to ask for specialist advice. There may be walls which are colder than they should be – causing condensation even in relatively ‘dry’ environments, or other causes, which need a bit more investigation.
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The Problem
Condensation is by far the most common cause of dampness in buildings, probably accounting for most dampness problems reported. It affects both old and new properties. Condensation is directly associated with mould growth, and it is this that the occupier first sees and gives an idea as to the potential scale of the problem. The mould is usually found on decorative surfaces, especially wallpapers, where it can cause severe and permanent spoiling. The mould and its spores (‘seeds ’) cause the ‘musty’ odor frequently associated with a damp house and can sometimes give rise to health problems.
The obvious places for condensation to occur are on cold walls and floors, but sometimes it occurs in roof spaces and in sub-floor areas where there is a suspended floor. Timbers in these areas will become damp and susceptible to damage by dry rot or wet rot.
The Cause
It is a fact that warm air can hold more water as vapor than cool air. So, quite simply, condensation is caused when moisture-laden air comes into contact with a cold surface –the air is cooled to a point where it can no longer hold its burden of water vapor. At this point, (DEWPOINT), water begins to drop out of the air, and it is seen as condensation on surfaces.
On impervious surfaces such as glass and paint, beads or a film of water collect, but on permeable surfaces such as wallpapered and porous plaster the condensing water is absorbed into the material. Therefore, the problem is initially not obvious.
Recognising Condensation
Condensation is very much a seasonal problem, occurring during the colder months (October to April). During the summer the problem is seen to go away. During the winter, ventilation of the house is usually low (windows and doors are closed, draught proofing takes place.) This allows buildup of water vapor in the house, which, in some cases, is sufficient to cause condensation. So during the colder months the following signs begin to appear:
In some cases, condensation may be long term but intermittent, forming only at certain times of the day or night. In these cases the only sign of condensation, may be mould growth, water perhaps evaporating during the day. One should also be aware that the problem can occur well away from the site of most water vapour production. For example, water vapour produced in a kitchen may diffuse through the house into a cold bedroom where it will condense on cool walls and lead to mould growth.
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A new technical publication on Salt Attack and Rising Damp has been published jointly by the Heritage Council of NSW and gives excellent advice for surveying a building for potential damp problems. The following is a useful list of activities you should undertake to help identify the extent of the problem.
Do go out in the rain (the heavier the better) and check gutters and downpipes for blockages, leaks and overflows. Also check around the base of the building for water lying against walls.
Do check for the presence of a Damp Proof Course (DPC) – and ensure that it is continuous, and not ‘bridged’ by built up paving and garden beds.
Do remember that damp walls increase the risks of fungal rot and termite attack to floor timbers – always check beneath timber floors.
Do consider the possibility that your old building may have had previous treatments for rising damp, and that these may be obscuring the extent of the problem.
Do clean out existing air vents regularly – and monitor results before deciding to add new ones.
Do consider the possibility of salt attack decay into wall cavities – always inspect cavities for accumulation of debris (and corrosion of ties).
Do consider the implications of drying out the soils beneath your building. If it is founded on reactive (expansive) clay soils excessive drying could lead to structural cracking as a result
of differential settlement.
Do get independent advice – that way there should be no pressure to use a particular product or system. Check your adviser’s credentials.
Don’t use hard cement mortars to repoint failed lime mortar joints – that will just drive the damp further up the wall and may also damage the bricks.
Don’t even think about sealing walls with water repellent coatings.
Don’t mulch your walls. Move garden beds away from the base of walls and remove irrigation to prevent spray and pounding against walls.
Don’t dismiss the old tar and sand DPC – reduce the damp ‘stress’ on the walls, repair the DPC, use sacrificial mortars in the joints if necessary, and monitor results before considering an expensive new DPC.
Don’t undertake insertion of any form of DPC until all the basic housekeeping measures have been completed and their effectiveness assessed over a period of time (at least a year).
Don’t accept the cheapest quote for chemical damp coursing without checking the contractor’s references and the details of the proposed works, such as drill hole spacing and depth, and how the contractor will determine when sufficient fluid has been impregnated.
Don’t try to get away with using less chemicals and then locking in the inevitable damp with waterproof plasters – your client has read this too!
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The causes of penetrating damp are multiple and can be related with faulty building work, poor maintenance, faults in the plumbing work or rain water goods which have allowed water to enter into the structure. Some common faults are leaking gutters, down pipes, ignored overflow pipes, dilapidated pointing, frost damaged bricks, faulty joints between window and walls, missing roof tiles/slates faulty or missing flashings all of which has allowed damp to soak through the building.
Penetrating damp result in serious deteriorating affects to the internal finishing like damp staining, salting, blown plaster, spoiling and peeling of the finishes in the internal areas. A watermark might be noticeable on the internal wall and grow if the water continues to enter.
Identifying the source of the dampness is of the up most importance. And the cause has to remedied before any remedial action can be undertaken. It must be noted that even when these defects can be cured, the effects of residual moisture within the building can continue to create problems. It is generally accepted that a wall can take one month for each inch of the wall thickness to dry out after the source of the penetrating damp is removed. So on an average 12” solid brick wall it could take a year to dry out.
Remedial Treatment
After identifying and fixing the root cause of the damp it will still take a long time for the wall to dry. The affected area will also be inclined to attract any available moisture. This moisture can manifest as mould associated with condensation. This is a result of the lower thermal properties of the wall hence making it colder. Wall coverings may appear damp especially after rain. It is possible to form a barrier by installing a studded damp proof membrane (moisture and vapour can evaporate because of the studs). Once they are installed, they provide a permanent separation barrier between the damp walls and internal finishes meaning a dry interior surface and protection is maintained always and the damp walls can dry out – meaning no more damp mould. Also Damp Proof Membranes are totally impervious to the hygroscopic salts which are bi-products of the penetrating damp and associated residual moisture. These membranes cover the entire wall and allow for plaster to be put directly onto them or for the application of plaster slabs. This allows for very speedy remedy to the problem and decoration can take place within a few weeks as opposed to a year.
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Salt attack and rising damp are two distinct but interconnected processes; both must be understood if damage is to be reduced and if corrective measures are to be successful. While the term rising damp is commonly used to cover both features, it tends to overlook the role of salt. The issue is more relevant in older buildings as the problem develops over time and concentrations of salts become more prevalent.
Salt damp is a term widely used in Ireland and the UK to refer to high salt concentrations associated with rising damp. The term is quite appropriate, as it merges the two concepts of salt attack and rising damp.
Therefore the approach recommended is to treat a salt damp problem as one requiring thorough understanding of the causes, as well as ongoing attention if it is to be managed successfully.
Already discussed in the previous blog were the causes of damp so I will concentrate on the salt aspect of the problem. Salt attack causes the decay of building materials such as stone, brick, mortar and renders. This occurs as the salts crystalize within the fine pores of the material. As the crystals grow they excert pressure on the material and cause disruption and decay. These salts are commonly found in the soil beneath the building and are transported up into the walls by the process commonly known as rising damp. As the dampness evaporates from the walls it leaves deposits of salts; as the salts cannot evaporate. The process of wetting and drying is somewhat seasonal and the cycle leads to the buildup of salt contaminants. It must be noted that these salts are not always noticeable.
Once salt concentrations are high enough for them to cause damage it will be necessary to treat the damp and salt problem if treatment is to be successful.
Sources of salts in walls may be one or more of the following:
• Saline soils and groundwater
• Sea-spray for coastal sites
• Air-borne (meteoric) salts — even in inland locations
• Air pollutants
• Inorganic garden fertilisers
• Biological sources — pigeon droppings, micro-organisms,
• Salt naturally occurring in the stone, brick clay, or mortar sand
• Salty water used for puddling brick clay or mixing mortar
• Salts used for de-icing roads in cold climates
• Cleaning compounds that contain (or react to produce) salts in walls.
The type of salt may be a guide to its source; e.g. high levels of nitrate salts
may indicate leaking sewers or confirm that a building was once a stable.
Next blog will give a detailed treatment plan for salt damp.
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View our video blog at ( http://www.youtube.com/watch?v=oHqHMzuG2CM )
Rising damp is caused by capillary suction of the fine pores or voids that occur in all masonry materials. The capillaries draw water from the soils beneath a building against the force of gravity, leading to damp zones at the base of walls. In most cases that dampness will have salt associated with it. The salt commonly comes from the soils beneath and is carried up into walls by rising damp. When the dampness evaporates from the walls the salts are left behind, slowly accumulating to the point where there are sufficient to cause damage. Repeated wetting and drying with seasonal changes leads to the cyclic precipitation of salts and the progressive decay of the masonry. Once salt concentrations are high enough to cause damage, repairs will only be successful if they include treatment of both the damp and the salt. Therefore it is necessary to remove the contaminated plaster and re-plaster using a 3:1 sand-cement render incorporating a salt retardant additive.
Treating the rising damp; a damp-proofing cream is injected into 12mm holes drilled in the mortar course every 150mm apart and ideally 150mm from the finished ground level. The damp proof cream spreads in the wall before curing to form a damp proof course.
This is a very brief introduction to the mechanics of rising damp. I would be happy to hear from anybody who may have questions or opinions on this topic. I have also archived articles which I have used to form my own opinions as to the causes and treatment of rising damp.
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