A musty smell, mould in the corners, white salt deposits on the walls, plaster coming away — a common picture in basements and semi-basements. The first instinct is to replaster and repaint, but it soon comes back. Basement damp has several different causes, and each needs its own solution. So the first step is to work out where the moisture comes from.
Where the moisture comes from: four causes
- Water from the ground. After rain, water collects around the foundation and comes in through capillaries in the concrete, cold joints and cracks. Signs: damp and salt deposits low on the walls, worse after rain, sometimes puddles on the floor.
- A leaking pipe. Water appears whatever the weather. Signs: a wet patch by a pipe or where it enters the wall, unrelated to rain. Fix the pipe first, then everything else.
- Condensation. Warm, humid air settles on cold walls and pipes. Signs: the wall is evenly damp, there are droplets on pipes, no salt deposits. Waterproofing won't help here; the room needs ventilation.
- Water from above. A faulty downpipe, or a yard that slopes towards the wall. Signs: damp in one spot or high on the wall, appearing during rain.
A simple test
Tape a clear plastic sheet, about 50 × 50 cm, to the wall over the damp area and seal the edges. Leave it for two or three days. If droplets form under the plastic, on the wall side, the moisture is coming through the wall. If they form on the outer side of the plastic, it is condensation. This is a clue, not a diagnosis, but it helps when you talk to the engineer.
What doesn't work
- Plaster and paint on a damp wall. A finish applied before the water is stopped will come away. Plasterboard only hides the problem.
- Ordinary coatings from inside. Water pushes from the other side of the wall and tears them off the concrete.
- Bitumen mastic on the basement floor. Water tears it off within a season.
- Removing the mould and nothing else. The product removes the stain, not the cause: the moisture stays and the mould returns.
- A dehumidifier alone. It lowers the humidity of the air but doesn't stop water coming through the wall.
How a basement is waterproofed from inside
If the water comes from the ground and the outside of the wall can no longer be reached, we work from inside:
- Finding the cause. An inspection and, if needed, a control opening.
- Removing the old finish where it is wet or coming away.
- Stopping active leaks. A hydraulic plug where water is coming in, injections in cracks and joints.
- Treating the walls and floor. A crystalline or flexible cement-based coating that holds against water pressure.
- Pipe entries as separate details.
- The finish — only after all of that.
The engineer writes in the report what suits your basement after the inspection. For more on when the work is done from outside and when from inside, see the article on foundation waterproofing.
What can't be solved from inside
Working from inside is a repair, not a replacement for external waterproofing. Water keeps pressing on the structure from outside. Moving cracks and expansion joints need a separate detail with injection and flexible tape.
What to do right now
- Check the downpipes: water shouldn't run down towards the wall.
- Note when the damp gets worse: after rain or whatever the weather.
- Do the plastic sheet test and photograph the patches.
- Don't cover the walls with a new finish until the cause has been found.
You can read how the inspection works in a separate article. The inspection costs 100 ₾; if you order the work from us, we deduct it from the estimate.