Damp Flashcards
What are the three causes of moisture in buildings?
Rising damp
Penetrating damp
Condensation
How can you diagnose rising damp?
Discolouration of materials such as stained wallpaper, plasterboard, and brickwork including efflorescence
Rotten skirtings etc.
A Damp meter
Senses – smell, touch, visual
What are common causes of rising damp?
the use of vapour impermeable materials, e.g. cement renders;
building high ground levels over the years;
removing rotten timber floors and installation of solid floors; and
various forms of tanking for damp proofing to deal with the symptoms of damp.
What is the mechanism of failure that causes rising damp?
The movement of water (through capillary action) upwards through a porous material such as masonry brick. It is thought to be limited to 1m in height due to the converse gravitational pull on the water – but this is dependent on the material of the walls, rate of evaporation.
If the ground water contains salts, these will generally be manifested on the internal side of the building
What are common causes of DPC failure?
External bridging by, say, a concrete plinth or ground levels being above the DPC.
Poor jointing between DPC sheets or DPC to DPM.
What remedial options exist for treating rising damp?
Chemical DPC - If a DPC has not been inserted. This process involves the injection of a water repellent material such as silicone in liquid form being into a wall to form an impenetrable layer by flowing into pores and gaps in the brickwork/masonry. Once the masonry has dried out, then the wall can be re-plastered often with salt retardant sand and cement render which contains a waterproofing additive.
Physical - Install new physical DPC - Cut along a mortar joint / cut out brickwork and replace / install a new physical damp proof membrane.
Electronic – osmotic process - This system involves the introduction of a small electric current into the wall just above ground level through a series of copper anodes inserted into the brickwork. The charge repels the moisture and forces it back down the wall and into the ground.
Lower the water table - To reduce the water table which is saturating the soil, a land drain may be installed to the perimeter of the house.
What are common causes of penetrating damp?
roof leak
defective/missing DPC on a parapet wall
defective rainwater goods (classic blocked hopper)
underground service pipe leaks, exposure (i.e. sea facing wall)
erosion by splash-back from surrounding surfaces (i.e. path, road, other hard surface)
How can you diagnose condensation?
Condensation can be felt on the surface of a material
Mould and mildew
What are common causes of condensation?
introduction of measures to improve thermal efficiency often reduced air circulation
Increase warmth of building has increase humidity levels as allow air to carry more moisture
What is interstitial condensation?
Interstitial condensations can occur where warm moist air is allowed to meet a cold surface such as within a flat roof that lacks an effective vapour barrier or ventilation at the eaves.
What is cold bridging?
This occurs where materials with high thermal conductivity (e.g. aluminium or concrete lintels) provide a path for condensation and moisture may be evident albeit intermittently/seasonally.
How are remedial options for condensation?
Need to improve ventilation, can be improved by:
- Inserting/Opening trickle vents in window frames
- Insert an air brick
- Unblock under-floor ventilation bricks.
- Introduce mechanical ventilation
- If problem is short term, a dehumidifier may be used to remove water from the air
