103H: Recent purchase deciding to chemically damp proof or not

This recently purchased Victorian was renegotiated for rising damp treatment, but the new owner had suspicions, so asked for a second opinion.

Surveyor Tips:

  • Talk to owners, mention your concerns and ask them about their habits – there was a strange damp patch by coat hoocks, which clearly came from hanging up damp coats.

Root cause

Penetrating damp from faulting guttering and condensation.


Damp wall

The chemical injection drill holes suggest the house has been damp proofed against rising damp at least twice. 

Damp wall

I use a damp meter to help identify dampness in walls.

I tested the surface 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. The range is 8WME to 99WME. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.

Damp wall

I use a radio frequency damp meter for rapid scanning and for determining risk of damp at depth.

I also tested walls in radio frequency mode. 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. 

These metres are not considered reliable enough to determine dampness and so are not used to by standard surveyors, such as during a homebuyer survey. From a homebuyer survey perspective the front walls were dry.

Damp wall

The high damp meter reading corresponded with cold external sub-floor vent and a crack in the windowsill.

The crack on the windowsill and flaking paint should be filled, painted and checked annually. There were no signs of water penetrating through which tends to leave a stain. Therefore I conclude that the likely damp deep within the wall is caused by thermal bridging increasing resulting in condensation.

Damp wall

There was a high damp meter reading to the rear reception.

Damp wall

As you rightly pointed out this dampness is caused by a leak to the toilet cistern.

I measured around the cistern. There were plenty of high damp meter reading in the bricks and timber. It is my view that there is no ongoing damp and that the wall will dry out over about 6 to 10 months.

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The plasterboard wall is still marginally damp. 

From the colour the wall was probably much damper, suggesting that the leak is fixed and that it is drying out.

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There is dampness on the external toilet wall up to about 1.5 m. 

It is likely that the metal in the extractor fan wiring is causing heat loss, slowing the speed of evaporation.

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The kitchen wall is also marginally damp.

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You have dampness on the wall behind the kitchen sink. 

The corrosion on the copper pipe suggests that moisture is condensing on the cold pipes. Water comes into the property at about 8°C in winter increasing the risk of condensation.

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There is a gap behind the tap.

The gap behind the kitchen taps should be sealed up. The area under the kitchen sink should be regularly checked for leaks and signs of condensation.

Damp wall

At the other end of the kitchen there is damage to the rear section of the party wall.

Damp wall

If you look closely you’ll see that there is a gap between the vertical tiles and floor tiles.

There are a number of compounding issues with this section of the party wall;

  1. External walls have been damp proofed against rising damp. Normally absorbent plaster is replaced with impermeable slurry, this increases the risk of damp to remaining walls.
  2. I suspect the plaster is touching the floor. Plaster is much more absorbent than brick. There should be a gap of 10-20 mm between plaster and a solid floor, otherwise there is an increased risk of water being absorbed upwards. 
    1. Water from the washing floor can easily be absorbed upwards.
    1. Water from condensation is at risk of condensing on a cold solid floor.
  3. It is possible that the neighbour also has a damp problem.
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The right hand rear corner was the coldest section of wall at the time of the survey.

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Heat loss is highlighted in the thermal image.

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The party wall to the front has dampness in the corner.

The pattern of darkness is triangular, this is consistent with condensation, which forms on the coldest part first and drops down through gravity to create a triangular profile of damp.

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The high damp meter reading is rise back up towards the coat hangers.

I was satisfied that this damp was most likely to be caused by damp coats and was not a sign of water coming in from the neighbour, above or under the floor.

Damp wall

There is rot in the skirting board.

This is difficult to be sure without seeing the fruiting body,  but I believe this rot is Coniophora puteana, or cellar rot, a brown wet fungus, see surveyor.tips/rot. Rot requires water to grow. Without water rot will die.

Damp wall

I measured the timber and found it to be at normal dryness, well below 28 WME required for rot growth.

My view is this rot will not cause ongoing damage, but it is better to replace rotten timber.

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In the rear bedroom there was a dusting of mould.

Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface. See surveyor.tips/mould. The secondary cause of high relative humidity is low temperature relative to the source of humidity, see surveyor.tips/humidity.

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Heat loss is visible through thermal imaging camera where blue it is about 5° colder than yellow.

Mould corresponds to cold patches. Note the wall appears to be made of breeze block, I suspect that the wall has been rebuilt, possibly following bomb damage.

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I measured the wall.

There are no signs of condensation.

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The source of the damp is bound to be the bathroom which has no extractor fan.

You can ventilate by keep in the window open and door closed. But you may find it beneficial to install a fan, such as a continuous flow bathroom extractor fan, see recommendations.

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That was the sign of a water leak which I tested for dampness it is currently dry.

There is a damp streak across the master bedroom ceiling. This looks like interstitial condensation caused by condensation forming within the ceiling or roof above.

Looking through a thermal image you can see a distinct loss of heat under the central valley.

I have saved many tens of thousands, from unnecessarily replacement of roofs because of intestinal condensation. Follow the recommendations. If damp persists, measure relative humidity and log dampness in the roof comparing it to weather conditions and humidity.

Damp wall

There is discolouration in the upstairs toilet which looks like rainwater penetrating.

The tea bag like stain is a sign that water is passing through brick or over timber.

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The wall is not especially damp.

Occasionally dampness is a sign rainwater goods of fail when there is a massive deluge of rain or when wind is blowing in a particular direction.

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Looking immediately outside we can see the timber fascia is showing signs of rot it should repainted.

From studying the gutter, I think they are too likely issues;

  1. Water flowing from the downpipe from the upper roof hopper, is likely to splash over the top of the gutter.
  2. The gutter is angled down by about 30 – 40mm too much, allowing water to splash from the gutter onto the fascia.

I recommend filming this area during a rainstorm to see what is actually happening.

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The property as a whole (front and back) has a lot of render cracks that should be raked out and filled.

Use external acrylic caulk for small cracks and use similar of type of render to the existing render, to fill larger cracks (probably cement-based mortar).

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I would also fill around ducting like this boiler flue.

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