Risk Factors
 When discussing damp and the risks of damp, it is important to realise that moisture itself is not harmful or dangerous in every context. Thus water in a plastic bottle in the refrigerator presents no risk to its surroundings – in sharp contrast to free water on a parquet floor. The plastic bottle is made to withstand water, whereas the parquet floor is exposed to a risk of swelling unless it is totally protected by varnish. Another example is a concrete slab in an older building. There is no damp problem if its drainage is designed to the prevailing standards of the day, but if a vapourtight surface is applied in the course of rebuilding (e.g. plastic flooring in a playroom) an obvious risk arises. So long as the concrete surface was free from the impermeable layer, the moisture transmitted inwards through the concrete slab was in balance with the moisture removed via the ventilation system. After installation of the impermeable layer, the flow of moisture is blocked, that can cause damage to the layer .
Some common hazards arising from the effects of damp are discussed below.
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| Deformation of materials |
Damp can cause materials to deform. This applies to all materials with a porous structure into that water can penetrate. For example, wooden materials are especially porous. On the other hand, deformation of concrete or cement mortar is so slight that it can normally be ignored. Mixtures of gypsum and cement may be subject to extreme swelling on exposure to moisture. maxit's levelling compounds are formulated to have similar properties to concrete and cement mortar despite having some gypsum content.
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| Transport of aggressive substances |
Damp can transport aggressive substances such as dissolved salts (free ions) and especially OH–ions that can create an aggressive alkaline environment. Alkaline damp can cause the breakdown (saponification) of adhesives and floor-coverings and coatings. This breakdown may give rise to foul-smelling emissions. For older types of concrete-floor paint it was essential to allow the concrete floor to dry out and the carbon dioxide in the air to neutralise the surface by carbonation before applying the non-alkali-resistant paints of those days.
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| Promotion of biological activity |
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Damp can promote biological activity such as formation of mould or rotting of wood. If wood and other materials of biological origin such as wooden tiles remain in contact with moist concrete they can develop mould, that in turn may generate unpleasant smells and possibly allergenic spores. The formation and growth of mould are highly dependent on moisture. However experience shows that raised alkalinity combined with restricted availability of oxygen combats biological activity in damp environments. According to Gravesen S et al, Statens Byggeforskningsinstut 2002, an RH of at least 95% is required for moulds to grow on plaster and concrete surfaces. |
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