How to treat damp patches on interior walls?
Damp patches on walls in bedroom or living room not only derogate building appearance but also damage structure and health. Dampness may lead to worsening of plaster, masonry, stones, tiles and also deteriorate timber work and expensive wallpapers.
Unfortunately, wrong treatments for dampness cause more damages and expenditures. Neither sealing walls with tiles or any other material provides a long term solution nor let the walls breathe. Breathability of buildings is required for building structures.
There are three most common causes of dampness:
1. Rising damp
2. Penetrating damp
3. Condensation or damp in moistures/air
Let us discuss these three causes and its solutions in details.
Rising damp is limited to lower part of walls and is caused by capillary action of ground water. Though, damp proof course is generally applied but ineffective damp-proof membrane or barrier cannot stop water to rise. If rising dampness is ignored, it can damage brick, concrete and wood work.
In new constructions, instead of any membrane based application in damp proof course, good quality water proof chemicals should be used in DPC concrete that make entire DPC as a water barrier. Membrane or any plastic sheet used in DPC have high possibility of tear or break during masonry work.
In old construction, rising dampness can be solved by industrial grades cementitious coating on mother surface of walls and by protecting coating by plaster. Waterproof coating should be air and vapor permeable so that dampness cannot come outside but can evaporate. Another precautions that should be taken care is to treat some extra area along damp patches else dampness will come out from closest area. Vapor permeability of coating and by providing some extra area to coating, help coating to let the water evaporates without letting it visible.
It is caused by water seeping through walls at any point. Usually, we have damp patches on walls that have bathroom or sunken portions on other side of walls. Roofs, parapets and any construction joints are possible source of rain water penetrations. Prolonged rain with high intensity and poor materials used in structure can cause water seepage even in vertical walls. Leaking drain pipe or fittings are other prime sources of water seepage.
Water leaking source should be repaired and waterproof coatings should be applied on damp area. In some case, house owner does not have control over water sources for example, if water seepage source is neighbor bathroom. In such scenarios, coatings and protective plasters can be done at damp areas. It would work similar to above treatment of rising dampness.
Condensation or damp in moistures/air
Warmness in house can cause moisture to evaporate in the air. On the other hand, if windows and doors are being shut, fresh air cannot replace air. As we all know, when humid air comes into contact with cold surface, it condenses and cools droplets of water. In cold weather, temperature of external walls is lower than air indoors and hence moisture condenses and run down on plaster or wallpaper.
We can reduce it by improving ventilation and insulation. Additionally, we should use water repellent chemicals on wall plaster to protect walls by providing positive waterproofing. There are chemicals available that can be simply sprayed even on existing plaster.