Electric sockets

Electrical sockets are made from cutting a section of wall out, replacing the plaster and inserting metalThe resulting damp risks are…

• reducing wall insulation from the cut-out, especially on colder lower section of wall,
• metal wiring and electrical box, looses heat rapidly, causing localised heat loss,
• wiring is often chased into plaster close to the surface.
• wiring often comes into contact with cold external temperature, either from the sub-floor void or outside walls.
• the new plaster is often with “bonding” plaster which it absorbent. The interface between permeable “bonding” plaster and a more impermeable plaster, and with the impermeable metal box increases the risk of moisture build-up in the interface.
• If the wall was previously damp proofed with impermeable plaster, cutting the damp proofing layer effectively puncture the damp proofing. Unless the wall is below ground or there is high groundwater it is rarely worth replacing the damp proofing plaster.

At night the wall temperature of an external wall, with insufficient insulation or heating, shaded from the sun on the outside, may drop below the dew point, that is the temperature when condensation starts.

Tips for solving damp

Illustrations and explanations

The primary concern was dampness that had caused electrical failure at sockets to the rear of the building.

The wire is corroded. Unusually the metal screws on the electrical connectors have rusted. The corrosion looks like it has been caused by atmospheric moisture through condensation. Sockets are prone to dampness as a section of wall is cut out, a metal box installed and covered in absorbent plaster, all of which exacerbate the effects of heat loss increasing the risk of condensation.

The bathroom external wall was damp as identified by a damp meter in radio frequency mode.

Mould is growing on a nearby wall.

Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface. See surveyor.tips/mould. The secondary cause of high relative humidity is low temperature relative to the source of humidity.

Mould is inhibited by nitrates found in groundwater. The presence of mould eliminates rising damp as the root cause and points to condensation.

The wall temperature was about 4°C below the ambient temperature.

Condensation is caused by high humidity and low temperature. When it is cold outside there is likely to be greater heat loss along this wall and in sockets. For each 1°C the relative humidity will be about 5%RH higher.

Carnivorous pitcher plants thrive in humid conditions.

The Venus fly trap was purposefully being kept humid and warm. The presence of an unvented kitchen and nerby bathroom with poor ventilation increased internal humidity.

There are damp spots in the cupboard near cold wiring.

Tips for dealing damp by metal sockets

1. Monitor risk of condensation with a data logger and where opportune:
   • Improve ventilation in nearby wet rooms.
   • Use a dehumidifier near vapour source, as identified by the data logger.
   • Improve insulation.
   • Improve heating, especially at night and in cold rooms with cold external walls.
2. Consider reducing the risk of metal causing heat loss such as:
   • Replace the metal box with a plastic electrical box.
   • If the wiring is causing condensation,
     • chase wiring deep into the wall,
     • insulate wiring on the inside and outside.
3. Replace the plaster around the metal box or wiring with plaster less able to absorb moisture, such as Sika or Dryzone Damp-Resistant Plaster. This is particularly relevant if the socket has been installed after the wall was damp proofed. 
   NB moving the interface between impermeable and permeable surface away from the metal is beneficial. However there is still a risk is damp could form on the new, larger interface between the new and old plaster.