The problem with damp

By Ellyn Peratikou

Damp can affect any property, large or small. It may not be immediately obvious and could take several years before visible signs begin to appear.

There are many reasons for damp developing in a property, for example lack of maintenance, deterioration of the building fabric or poor build quality. Most damp problems will be linked to one of three main issues:

Rising Damp – here ground water is drawn upwards through bricks, mortar and other porous building materials used to construct walls. The speed at which this occurs depends on several factors – type of construction material, levels of ground water and rate of evaporation. In the majority of cases rising damp is a fairy slow process, taking several years to develop before tell-tale signs appear.

Signs of rising damp

  • Damp, discoloured ‘tide marks’ on internal walls, caused as the salts in rising ground water accumulate.
  • Blistered paint and stained, peeling wallpaper.
  • Fragmenting and blistered plasterwork.
  • Rotting skirting boards and floor timbers.

Penetrating Damp – occurs through walls, roofs, windows or door surrounds and will eventually cause damage to the property. There are two main causes of this type of damp:

  • Building defects – cracked pointing, faulty guttering, damaged down pipes, defects in roof tiles, blocked weep holes or defective seals.
  • Lateral water penetration – caused when external ground abutting the walls is above the internal floor level.

Penetrating damp occurring through horizontal movement (rather than upward travel as with rising damp) is more likely to affect older buildings with solid walls – as cavity walls can provide some protection.

Signs of penetrating damp

  • Damp patches on walls, floors or ceilings, often darkening after heavy or prolonged rainfall.
  • Musty smell.
  • Blistering and damaged plaster.

Condensation – the most common type of damp, occurring where high levels of humid air are trapped within a property and poor ventilation does not allow its escape. This moisture condenses when it touches cold surfaces such as windows, walls and ceilings. Sometimes this can happen in hidden areas such as roof voids or suspended floors, making timbers in these areas susceptible to rot.

Signs of condensation

  • Mould growth (often black) – along window edges, skirting boards, behind furniture or on decorative surfaces.
  • Musty, damp odour.
  • Peeling wallpaper or blistered paintwork.

It is important to identify a damp problem as quickly as possible so that it can be effectively treated by professionals before any damage becomes more serious and more costly to repair.


About the author

Property Care is a specialised division of Rentokil working in the field of woodworm treatment and damp proofing for over 60 years. We work with residential and commercial customers across Britain, covering areas from London to Glasgow, and provide house surveys for home buyers.

Rentokil technicians provide specialist treatments for rising damp, dry rot and cavity wall ties as well as dealing with damage caused by wood boring beetles. Download our brochure for more information on “Protecting properties against Woodworm, Damp and Rot“.


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