Usually we realized a damp wall lately. When the paint has begun to peel off the wall and overgrown with moss, then we realized that the wall is damp or wet . Damp wall can cause health problems.
Some damp wall causes :
Rainwater leaks from porous cement duct. It is easy to find the cause, as the wall is only damp when rainy season. The water may not directly go down to the floor, but absorbed in porous wall. Cement plaster and sealant can help to avoid leaking duct.
Roof with concrete duct as shown above, usually built in tight space. Sometime the wall is directly adjacent to neighbors yard, and no part of the roof is covering top of the wall to avoid rainwater goes into neighbor yard.
Concrete duct of the above design collects rainwater from the roof. But sometime that concrete duct is cracked that allow water to seep into wall. Sometime we cannot find any water droplets on the floor, but the rainwater is absorbed by the wall, and creating very humid air inside the room.
If needed, remove some old plaster around cracked duct, as it is a clue that the old cement mixture has too much sand. Re plaster using better mixture, 1 part of cement with 3 parts of sand, if needed use minimum sand or cement only to cover the crack. Then put waterproofing membrane onto duct.
Water line leaks
Water leaks can occur in water pipes from the pump, from the tank or reservoir, or from municipal water supply network. Water supply pipe must not be covered by cement, because it would complicate the repair if leaking. Water supply pipe leaks not only waste water usage. Leaking water pipe can also lead to contaminated water in it. In some countries, tap water is drinkable before boiled. Because tap water quality standards in that country must be as good as drinking water, not only for washing and cleaning standard. This is where the role of expert plumber needed to apply simple yet functional pipeline and easy to repair if damaged, and ensure nothing dirt enter.
For reasons of beauty, often clean water pipe is installed hidden in the wall. Hidden water pipes will be difficult and costly to fix as we need to open the wall, especially if the walls are covered with tiles like in bathroom and kitchen wall. Sometime the easiest and cheapest way to fix leaking pipe is by closing the leaking old pipe and replace it with a new pipe with different pipe path.
Cement sewer line (concrete duct) is not watertight and water will seep into the walls. It is not very easy to put sealant on to duct surface as many dirt deposit. The most effective solution is to replace the concrete duct with PVC pipe.
Water is Pumped Up by Capillary force
The occupant may get sick by damp air inside the house. But as there is no water leaking, and we cannot explain what is happening, then we blame some magical force is haunting the house.
Porous wall can suck water from soil by capillary force and causing confusion. We think that the water is coming from above, but actually it is coming from below as pumped up by capillary force. Tree uses capillary force to pump water from root up to the highest leaf which can be as high as hundreds feet.
Any water source near the porous wall, such as: flower pot, fish pond, wet ground, etc.
To much sand in wall mixture may cause porous wall, applying more cement and sealant may help to reduce wall pores and reduce capillary force.
Wet soil at the other side of wall may cause damp wall, if too much pores in the wall. This usually happen in underground building.