102K: lower ground floor flat, damp proofed without success

This one bedroom lower ground floor flat has been damp proofed at least once before even though there are no risks of groundwater. I happen to know that a large storm drain was installed near or under the building in about 2008, and may have disrupted the drains.

Root causes

The root cause was penetrating damp to rear, hygroscopic salts and possible broken drain under a solid floor.

Surveyor Tips

  1. I’ve seen thousands of damp proofed properties, each increases my scepticism about benefits of rising damp treatment. This is an example.
  2. Yes there is a problem, but it is not groundwater, the root cause of rising damp.
  3. Use your, the owner and occupiers, knowledge, especially changes that might have effecting a property.
  4. Be sceptical before diagnosing damp.
  5. Use desktop review of groundwater and flood risk.


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Damp meter reading is high on the wall surface in the corner of the reception and around the chimney breast.

I tested the surface on the inside at the base of all external walls every metre, chimney breasts and a sample of internal walls with a Protimeter damp meter in conductance mode. These meters measure electrical conductance of salts in water, a proxy for damp. Readings below 20WME are considered dry, see surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.

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I also tested walls in radio frequency mode. The meter reading indicates moisture deep in the reception corner.

Water reflects radio waves at a set frequency similar to mobile phone shields. Meters can’t differentiate moisture from other dense matter such as metal and concrete. They help trace damp in a normal, homogeneous wall. Readings below 300 REL indicate that a wall is dry below the surface, 999 REL is the limit. These meters are for scanning, mapping and profiling, see surveyor.tips/profile. 

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The wall around the chimney breast is damp deep within it.

Chimney breasts are prone to dampness. However, there was no significant decorative spoiling.

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The owner showed me the Kenwood quote for works to stop rising damp, completed in 2010.
Note the edit to remove the address.

I understand Kenwood’s work included injecting chemicals into the walls, and replacing the original plaster with impermeable damp proofer’ slurry. This has the effect of trapping dampness deep within a wall, see example of the Kenwood to work later in this report.

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I do not believe the property has ever suffered from rising damp. There are a number of more likely sources.

Here there is it cracked coping stone and missing section of render. Note the tubes drilled into the wall, this is another form of damp proofing against rising damp.

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In the above image there was damp soil up against the corner of the reception wall.

The missing render to this section, to the rear of the reception wall should be rendered, consistent with the rest of the wall. The gap should be filled to stop water flowing in.

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There are some render cracks.

Horizontal cracks can allow lot of rainwater to penetrate. These cracks should be raked out and sealed with either a cement-based render, or acrylic caulk, and repainted.

There are signs of hygroscopic salts on the rear wall.

Hygroscopic salts cause condensation at normal levels of relative humidity, see you later.

I note there are chimney stacks on the left-hand party wall. This maybe the source of hygroscopic salts.

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There is a horizontal scar along the wall by the front door. This results from damp proofers slurry.

We can tell that the whole of the left-hand wall has been damp proofed. However, this does not address the root cause of damp, unless indeed the root cause was groundwater the source of rising damp. It is more likely to result from hygroscopic salts, which are benign, or from a cracked drain, which may cause additional problem is left unattended.

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Measuring with a damp meter and radio-frequency mode we find that deep within the wall on the left hand side.

The surface of the wall is dry, but moisture appears to be trapped by the slurry. It may be innocuous, such caused by hygroscopic salts, but could also come from leaking pipe.

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I tested the mains water pressure, with the pressure gauge.

There was no detectable mains water leak. The next most common other source of water below ground is from cracked drains. I understand that a large stormwater drain was installed under these properties, in about 2008. I suspect, but don’t know that there has been disruption to the drains, and that there may be a leak under the property. The only way to know is to instruct a CCTV inspection of all drains running under the property.

Rising damp risk assessment

Elevation is: 24M above sea level.                 The flood risk is: Risk of surface water (i.e. penetrating damp from rainwater, not rising damp from groundwater).

Sub-soil rocks are: Rocks with essentially no groundwater.
Signs of groundwater: there are no signs of groundwater.

Therefore the risk of rising damp is a remote possibility, see a good explanation by  Dr Robyn Pender of Historic England  https://youtu.be/Jo8oF9ubvtI

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There are tell-tale signs of multiple damp proofing treatment against rising damp at this flat. 

Despite the low risk of rising damp, there has been an attempt at chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The walls have been drilled into by about 200mm and injected with damp proofing chemicals. In theory the chemicals are absorbed into the brick pores reducing the bricks ability to absorb moisture. Walls are replaced with damp proofers slurry. This can cause problems with absorption imbalance, resulting in increased condensation on other walls or vapour becoming absorbed and trapped behind the slurry. There was evidence of surface condensation in areas probably not treated with replacement plaster but no evidence of trapped vapour. The solution is through ventilation and humidity control.

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