How to remove mould from walls and ceilings
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Mould grows in those corners of the wall which are most prone to condensation, i.e. where there is less insulation from the outside, and this happens mainly with old walls.
So the best way to reduce mould growth on the walls at home is to prevent condensation, by dehumidifying the air or insulating the walls.
Dampness can be removed from the room with an electric dehumidifier or an air conditioner, rather than one of those plastic containers that you fill with salts which attract moisture, although the fact remains that these appliances need to be left on the whole day long in order to have the desired effect.
The walls can be insulated internally (with gypsum plaster drywalling, for example) or externally (the method of choice), although that is a pretty big job, one that a painting and decorating company would be well placed to take on.
External insulation usually involves applying panels made of insulating material (polystyrene) of various thicknesses (I would suggest at least 5 cm) to the outer walls of the building, on top of which a thin layer of plaster and the water-repellent paint is then applied; the insulating properties of the polystyrene combined with the water-repellent paint ensures high thermal insulation and greatly reduces the chances of seepage from outside. The downside of this kind of work in older buildings is that if not carried out throughout (i.e. walls, floors and the various interstices) then we are bound to be left with some thermal bridges, where condensation is bound to form, with the result that mould may start to appear in corners where there wasn’t any before!
Insulating the walls is even more effective at keeping mould at bay if carried out internally.
Let me explain… external insulation is great for keeping the heat in, but internal insulation is better if we are “only” doing it to protect ourselves from mould. If our home lends itself – i.e. if the rooms are big enough – then we can fit some drywalling made of appropriate materials (gypsum plaster, hollow brick+polystyrene, etc…), which from an aesthetic point of view will certainly be a great improvement on external insulation, because it will protect us from the problem directly where it actually crops up. We will have a “new wall” at our disposal (the surface of the wall will be new, that is) where the mould has never taken up residence before, and so it will be a whole lot harder for it to colonize anew, which is actually something that could well happen with external insulation, as the internal wall surface is the same as before.
If building work like this is out of the question, and let’s say we also want to keep our budget under control, the best way to deal with mould is to wash the walls with a non-foaming bleach (i.e. one without added soaps) or rather – even better – with a solution of sodium hypochlorite!
WARNING: household bleach is usually a solution of 5% sodium hypochlorite, so at higher concentrations the solute (the hypochlorite) is obviously more powerful, in every sense: if breathing in ordinary bleach fumes can give you a headache, you can imagine what the effect might be at stronger concentrations!
Sodium hypochlorite solutions are used mainly as bleaching agents and disinfectants, on account of their oxidizing action. Sodium hypochlorite is a bactericide, sporicide, fungicide and virocide. In solution it is also widely used for normal cleaning of washable surfaces. It is practically useless, however, against dirt. In fact its whitening effect gives treated surfaces the illusion of cleanness but without actually being clean.
Bleach and sodium hypochlorite solutions are irritant and caustic, so it is as well to handle them with a pair of rubber gloves and to be careful to avoid contact with eyes. Nor must they be mixed with either hydrochloric acid (which may be known as muriatic acid for domestic use), as that would release chlorine, which is poisonous, or ammonia, with which they react to produce chloramines, which are irritants. The bleach kills the mould, which is a living micro-organism, and also helps whiten the area which it has discoloured. The mould, of course (sadly!) dies hard: although the bleach does a good job at surface level, it will certainly be necessary to repeat the treatment, as the mould which is still alive inside the walls will not waste any time in growing out and making an appearance once again.
There are some, indeed, who would recommend SETTING FIRE to the walls!!! I have not attempted this, but on paper it sounds promising, as the fire would exterminate the mould from the walls in a more radical way than the bleach would; those who have tried say that this trick has actually allowed them to get away without repainting for a number of years.
To sum up then, the best things we can do are (in order)…
- internal drywalling
- external insulation
- bleach (to kill off the mould)
- a dehumidifier/ air conditioner (to discourage it from growing)
- remembering to air the rooms!
A maverick viewpoint
According to one theory all the blame for the growth of mould in domestic dwellings can be laid squarely with poor ventilation, i.e. insufficient changing of the air in the rooms; on this basis, old houses, with their draughty shutters and window frames, would be preferable to modern ones, whose window fittings seal spaces and keep moist air inside the house.
The human activity of 4 people inside a house can produce on average 11 litres of water vapour per day, which is dispersed through the air inside the building. When the air gets too humid, this vapour condenses on cold surfaces (walls and ceilings) and quickly turns into water, which then remains trapped inside the pores of the walls. If you look closely, you can see that the mould mostly accumulates where there is less air convection, i.e. in the corners of rooms, where ceilings and walls meet, around window frames and behind the furniture.
The problems normally associated with the so-called thermal bridges, i.e. the wall or ceiling areas, are viewed as bogus in this theory, as the formation of mould in the corners becomes simply a question of the poor exchange of air in those parts of the room. The important thing to consider, though, is that the circulation of fresh air can help combat the excessive increase in humidity inside the house. In humid air, viruses, bacteria and spores spread everywhere, and they can even find a home in the particles of dust floating in the air.
Some moulds, such as Aspergillus, Trichoderma, Alternaria, Penicillium, Stachybotrys and Cladosporium, are toxic, producing allergens and even mycotoxins; these can cause disease and various types of ill health. Lots of people are allergic to mould, and their symptoms are the result of inhaling (and also contact with) the spores of these toxic moulds. Mould infections can give rise to a range of symptoms:
- redness, lachrymation, sensitivity to light, headache, dermatosis and dermatitis
- nose or throat irritation, congestion of the airways, dyspnoea, coughing and breathing difficulties …even to the extent of full asthma attacks
- influenza-like symptoms, leading to “pneumonia”
- memory problems and mood swings
Nowadays over 50% of modern dwellings are contaminated with mould, even if this is not visible to the naked eye. If we consider this, and reflect on the commonest of the symptoms described above, we can be led to the conclusion that everybody is suffering from some form of mould intolerance.
Some of the scientific names of mould fungi
Aspergillus nidulans, Aspergillus niger, Aspergillus versicolor, Aspergillus fumigatus, Aspergillus flavus, Penicillium chrysogenum, Penicillium expansum, Penicillium verrucosum, Penicillium viridicatum, Fusarium, Stachybotrys chartarum (atra), Acremonium, Alternaria, Aureobasidium, Basidiospores, Basidiomycetes, Poria incrassata, Botrytis, Chaetomium, Cladosporium, Trichoderma, Ulocladium.
Encyclopaedia Treccani defines mould as “A fungus which forms an abundant and not especially compact mycelium, whitish, greenish or black in colour, living on the surface of vegetable or animal tissues and a wide range of organic matter, as a saprophyte or, less commonly, a parasite. The metabolic products of some moulds inhibit the development of many microorganisms (e.g. Penicillium notatum, which was at the root of the discovery of penicillin).”
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