The appearance of dampness or damp rising in building is very ugly and makes a mess of your architectural edifice. If dampness are not properly controlled during the foundation of the building, it becomes so difficult to curtail when it start occurring. You must have seen at one time or the other the wall painting and the rendering start swelling and pilling off, this is caused by damp rising in building. Or when you look at the wall you will notice the lower part of the wall is wet while the upper part of the wall is dry this is one of the effects of damp rising in building. When you feel it with your finger you will feel coldness and wetness this is not a desirable effect in building at all. After sometimes it causes the fabrics of the structure to start getting weak and start deteriorating. It also harbours infestation of unwanted insects. Before we discuss how to prevent damp rising in building, let us discuss what causes damp rising in Building.
Effect of damp rising in building
CAUSES OF DAMP RISING IN BUILDING
- Damp rising is generally caused by strong affinity between cement and water. Cement which is used for the construction of building loves the presence of water and draws it to itself through what is called capillary action. When a dry cement block is immersed in a little volume of water you will notice that after a while the water completely vanishes or the volume reduces tremendously. You will now ask yourself what must have caused the water to diminish. The cement block literally absorbs the water and this is what causes dampness in building. The foundation of building is below the surface of the soil. Soil contains some percentage of water and some places are even water logged. So the building foundation immersed in soil water start absorbing water until it becomes completely wet that it can no longer absorb any more water. But mind you the superstructure which is the part of the building above the foundation is linked to the foundation so the superstructure starts to absorb the water present in the foundation. After sometimes the blocks at the lower part of the superstructure becomes wet and starts transferring the wetness to the neighbouring blocks. The foundation on the other hand feeling drained, absorbs more water to keep its wetness. The cycle continues until you start seeing wetness otherwise known as dampness, travelling upward. This is one of the causes of damp rising in building.
2. One very unnoticeable cause of damp rising is wall rendering what some people call plastering. Plastering is a mixture of cement and sand in a certain ratio. The same way cement block absorbs water that is the same way plastering absorbs water. Even though the damp proof membrane may be present beneath the oversite concrete. Since the plastering are done from the natural ground level, it therefore provide a bridge that conduct water to the block wall since the damp proof membrane don’t cut accross it.
3. Another cause of damp rising in building is the use of polythene sheets laid under interlocks. Nowadays we use polythene sheets to prevent grasses from growing in between the interlocks and to also prevent damp rising from the natural soil to the ineterlock tiles. But if not thoughtfully used it will on the other hand constitute a menace of damp rising to the building. This is how it happens: When rain falls, the polythene sheets do not allow the water to permeate into the soil. Therefore, the water stays on the polythene sheet looking for a way out. The block wall now says: hey! I have been so thirsty and now comes free water. It absorbs the water. After absorbing sufficient water, it starts transferring it to the neighbouring blocks.
Now that you have known what causes damp rising in building it becomes very easy for you to device a means to curtail its occurrence.
Rain water accumulation because of polythene under the interlock
STEPS TO PREVENT DAMP RISING IN THE BUILDING
The primary method employed to curtail damp rising in building is to use a means that disconnects the superstructure (parts of building above the foundation) from the substructure (foundation). We may not be able to prevent the foundation from dampness since it is hosted in the soil. But we can prevent it from transferring the wetness to the superstructure by using some devices to cut off the link between the foundation and the super structure.
- Use of damp proof membrane. These devices are called damp proof membrane (DPM). They come in various forms like polythene sheets laid neatly on a thin bed of concrete (blinding) before casting oversite. They literally disconnect the foundation from the superstructure so that when water travels upward the foundation the damp proof membrane says hey! There is no road here stop there!
- Use of engineering bricks. Engineering bricks are burnt bricks which are impermeable. When laid between the substructure and the superstructure, the form what is called Damp proof course (DPC). They don’t allow permeation of water.
- Use of wall reveals. Wall reveals are depressions made round the wall horizontally. It is employed to disconnect the rendering (plastering) of the superstructure from the plastering of the substructure. Best practice is to create the wall reveal at the location of the DPM or DPC. It should not be above or below. It should be at exact horizontal location of the DPC or DPM. Similar to what we had before, we may not be able to stop the rendering of the foundation from getting wet. But we can stop it from transmitting the wetness to the rendering of the superstructure.
- Wall projection and recession. When you project the wall of the superstructure from the alignment of the wall of the substructure either inwardly or outwardly, it disconnects the substructure rendering from the rendering of the superstructure. At this point rendering or plastering which also absorbs water is disjointed because the walls are not on the same vertical alignment, thereby preventing damp rising from substructure to superstructure.
- Do not interlock the whole compound. If you must use polythene sheet as interlock underlay it is not wise to fill the whole compound with interlock or pavement. Leave out some areas between the building wall and the interlock in form of flower bed. This flower bed allows the surface water to drain into the soil keeping the wall and ineterlock surface dry. This also prevents growth of algae on the interlock surface.
Flower bed around the wall
Worthy of note that, to achieve effective result, you have to combine the use of wall reveal or Wall projection and recession with any other methods listed above. Because if you use damp proof membrane or engineering bricks to cut off damp rising from foundation to superstructure. You should also use either of the two last methods listed above. Because if the plastering or rendering is flat from foundation to superstructure, it serves as a bridge which transmits water from substructure to superstructure thereby rendering your former effort futile.