Sources of moisture and moisture control

Sources of moisture in a building

1. Ground water rising by capillary action through foundations and walls (rising damp).
2. Rain penetrating through the roof, walls, parapets, windows and joints.
3. Condensation of water vapour on cold surfaces such as walls, ceilings and windows.
4. Leakage from water supply and drainage pipes, bathrooms and roof tanks.
5. Construction moisture in new concrete, mortar and plaster.
6. Defects in design such as poor drainage, no DPC, and flat roofs without slope.
7. Hygroscopic salts in bricks and sand.

Methods of moisture control

1. Damp proof course (DPC) at plinth level, 150 mm above the ground. Types: rigid (40 mm cement concrete 1:2:4 with waterproofing compound), flexible (bituminous felt, polythene sheet) or semi-rigid (mastic asphalt). DPC is also provided at sills, parapets and in cavity walls.
2. Integral treatment: A waterproofing compound is added to concrete and plaster.
3. Surface treatment: Waterproof cement plaster, water-repellent paint, pointing and silicone coating.
4. Cavity wall: An air gap that breaks the moisture path.
5. Roof treatment: Proper slope, brick-bat coba waterproofing, membrane, flashing at junctions, gutters and rain-water pipes.
6. Drainage: An apron around the building, sub-soil drains and ground sloping away.
7. Ventilation and vapour barriers to prevent condensation.
8. Chemical injection / grouting for existing damp walls.
9. Basement tanking.

   wall
   ======== <- DPC (150 mm above GL)
   ~~~~~~~~ ground level
   apron 750 mm wide, sloping away