Dampness in buildings is usually a ‘sorry sight’. It comes with many unpleasant features that can lead to mould growth, damage to belongings such as furniture, books, paintings, other finishing and important installations (see Figures 1 and 2). This is usually a continuous process once started and may have caused much damage before it is discovered if the position is hidden.
Figure 1: Effect of dampness in buildings 1
Figure 2: Effect of dampness in buildings 2
The best solution to dampness is PREVENTION. That is, taking appropriate measures to prevent it during the time of construction. The traditional method was to break the wall with oversite concrete but this method has proved unproductive with time partly because concrete often have micropores or develop micropores with time which enables passage of water.
In recent times, dampness is controlled with the use of substances that don’t allow passage of water and does not usually undergo degradation. Such materials as nylon bags, bitumen etc., called DPM (damp proof membrane) are commonly used (see Figure 3).
Figure 3: Damp proof membrane (DPM)
DPM is embedded in the foundation layer. See relative positions of DPM in foundation. DPM is a delicate material embedded within substances likely to damage it. There are usually controversies on the ideal position of DPM in foundation to ensure it is safe. Two common order is usually followed as shown in the table 1 below.
Table 1: Common order of placement and ideal position of DPM in foundation
If the measures above were not implemented on site maybe due to cost or incompetence or lack of proper judgement of the behaviour of foundation soil with regard to capillarity, and DAMPNESS HAVE OCCURRED, the only solution is to repair the wall. This can be done by following the steps below:
- Locate the walls with dampness.
- Break the walls at intervals of 1 – 1.5 m to a height of 100 mm to 150 mm (0.1 – 0.15 m) (see the Figures 3 and 4 below) through the walls such that you can see from one side to the other (Note: In situations where the walls are liable to collapse, use props to support the walls).
Figure 3: Opening patterns of wall to repair dampness 
Figure 4: ‘A’ - Prepare a good concrete mix preferably at ratio of 1: 1.5: 3 using a good and clean sharp sand with about 12 mm crushed aggregate (chippings) and potable water on a neat platform. Mix one bag at a time to ensure thorough, uniform and consistent mix. The essence of these is to produce a very strong and durable concrete. Mix the concrete first in the dry state.
- Add a prescribed percentage of water-repellant substance (e.g Dr fix commonly used in Nigeria) to the required quantity of water before using it to mix the cement thoroughly. Let the concrete mix have good consistency.
- Protect one side of the wall with formwork and fill up the created hole with the concrete and tamp properly.
- Do these at intervals and when you are done with the opened walls, open the rest and continue the same process until the entire length of the wall is completed.
- When completed, scrap the other damped sections of the wall and re-plaster with a mortar mix of cement: fine sand at a ratio of (1:3 – 1:4).
- Leave the plastered wall for at least five (5) days to cure properly before applying paint or other finishing.
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