How Long Must a Damp Wall Dry Before Replastering? Ghana
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Once the source of water is stopped, a block wall dries at roughly one month per 25 mm of thickness. A 150 mm wall wet right through can take several months. Nobody wants to hear that, which is why most damp walls get replastered too early and fail again.
Why it takes so long
Water does not sit on the surface of a block wall — it is held throughout the material, in pores and capillaries. Drying only happens at the faces, by evaporation, and the water deeper in has to migrate outward before it can leave.
That migration is slow, and it slows further as the wall dries, because there is less water to drive the movement. The last 20 percent takes disproportionately long.
Dense blocks and cement-rich mortar dry more slowly than soft, porous materials. Walls that can only dry from one side — a boundary wall against earth, or an internal wall with something fixed to the other face — take roughly twice as long.
The polythene test
Forget guessing by eye or by touch. A wall can feel dry and still be carrying plenty of water.
- Tape a square of clear polythene, around 500 × 500 mm, tightly to the wall on all four edges.
- Leave it 24 to 48 hours.
- Lift it and look. Condensation on the underside, or a darkened patch of wall beneath it, means the wall is still releasing moisture.
- Repeat weekly in the same spot until it comes away dry.
Test in several places — the base of the wall will be behind the top. Test the worst spot, not the most convenient one.
What Ghana does to the timetable
| Period | Effect on drying |
|---|---|
| Harmattan, December to February | Best conditions of the year. Dry wind does the work for you. |
| March to April | Still workable, humidity climbing. |
| May to July | Main rains. Drying effectively stalls. |
| September to November | Second rains. Poor. |
This is why damp wall work should be planned for the dry season. A wall stripped in June will not dry before you are forced to close it up, and you will have spent the money for nothing.
How to speed it up
- Strip the old plaster off. Counter-intuitive but correct — exposed blockwork dries far faster than blockwork sealed behind render.
- Open the room up. Cross-ventilation, windows open, air moving.
- A fan beats a heater. Air movement across the face removes the saturated boundary layer. Heat alone just raises humidity in a closed room.
- Clear vegetation and raise ground levels away from the base if the wall is external.
What does not work: sealing the wall to "keep the damp in", or plastering with a waterproof render to hold it back. Both trap moisture and move the problem higher up the wall.
When the wall is finally dry
Blockwork that has been wet and then dried is usually weak and chalky at the face — the cement paste has been leached. Plastering straight onto it means bonding to a dusty surface.
A sand fixing agent penetrates 5-10 mm and consolidates that layer. It is a small step that protects a much larger one, in the same way surface preparation protects a waterproofing membrane.
The honest conversation to have
If a contractor tells you a wall that was soaking in October will be ready to plaster in November, they are telling you what you want to hear. The wall does not know the programme.
Better to leave it exposed through Harmattan and plaster in February than to close it up in November and strip it again next year.
Not sure if your wall is ready? Call 0555 548 001 or 0241 737 026, or book a free assessment in Greater Accra.
Related Resources
- Why Plaster Keeps Falling Off Damp Walls
- Hollow-Sounding Plaster — The Tap Test Guide
- Substrate Moisture Test Before Waterproofing
- How to Stop Damp Walls Permanently in Ghana
- Why November to March Is the Best Time
Fest Ghana Limited is the trading name of FGL Waterproofing Solution Limited Company, a company registered in Ghana — Registration No. CS218171026. Company information.