Victorian house with a quote for £20K Kenwood chemical damp treatment turned out to be a blocked drain.
Surveyor Tips:
- Rainwater drains are commonly the cause of rising damp type symptoms.
- Pour some water in and see what happens above and below ground.
- Recommend a darin CCTV.
Root cause
Blocked drain, condensation and penetrating damp from the roof or chimney.
Illustrations
The building has been damp proofed against rising damp, the horizontal covered drill holes across the centre of this image, is a sign of chemical damp proofing, hear what Dr Robyn Pender of Historic England says about it.
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.
There are signs of past dampness to front walls. I’m told these were damp and mouldy during the RICS survey.
I understand that there were tenants in the property and mould was growing in ground floor corners. 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.
Mould is inhibited by nitrates found in groundwater. The presence of mould at the bottom of a wall eliminates rising damp as the root cause.
I measured the surface moisture of walls using a damp meter – the base of most walls were dry.
I tested a sample of 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. The front walls were all dry, which quite different to the prepurchase survey and quote.
If the front bay and chimney represents about half the cost of the damp proofing treatment, then, you have already saved yourself about £5,000 by doing nothing, other than keeping occupancy levels lower than when the property was rented.
To save an additional £1,000 I treated woodworm on ground floor timbers with Permethrin.
I don’t believe the woodworm was active, as a) there were no signs of frass, the excretion left by woodworm, b) the timber has been stripped, exposing tunnels, c) there are tiny holes highlighted, these are caused by the larvae of parasitic wasp, which feed on woodworm.
I tested walls in radio-frequency mode, these can detect density about 70mm deep within the wall.
Protimeter radio-frequency meters are used for scanning and determining residual damp. Above 300REL needs further investigation. Meters can’t differentiate moisture from other dense matter such as metal and concrete. They help trace damp in a normal, homogeneous wall. 900REL is used for profiling damp, see surveyor.tips/profile.
Looking through the thermal imaging camera where blue is about 5° cooler than yellow.
We can see considerable heat loss to the front bay. Heat loss increases the risk of condensation and mould, and slows down the process of evaporation. Bays are at risk of heat loss because they have greater surface area on the external side of the wall. Plants and other objects reduce airflow. The bay is far from heating, creating heat imbalance.
There was a marginally high damp meter reading in the corner of the rear reception.
A short distance away the meter reading was low. This profile is typical of condensation, not rising damp.
The radio-frequency meter shows that there is residual dampness deep within the wall.
It can take up to 10 months for a wall to dry out, and longer in humid conditions.
Corners and doors or window surrounds lose heat rapidly increasing the risk of condensation.
Cold air becomes trapped behind objects.
There was a brown mark halfway up the left side of the rear reception wall.
Brown marks looking like teabag stains, are a sign of penetrating damp from rain. As we will see you later in the report, it appears that the rear guttering had failed above, but was repaired some time ago.
There was a high damp meter reading by a light switch in the dining area.
Sockets are prone to dampness as metal boxes lose heat rapidly, see surveyor.tips/sockets.
The wall was quite down deep inside, up to the metal box.
Yet at the base of the wall the surface was dry.
The kitchen has no externally ducted extractor fan.
It is also likely that clothes were dried internally by the tenants.
There is an area of mould and surface salts on the external wall above the damp proofer’s slurry.
Slurry can block water, but does not stop the cause, unless the cause genuinely is rising damp. Calcium sulphate is a key ingredient in cement and other building materials. If diluted in water, salts tend to move to a surface. These can be removed with sandpaper, dried and decorated.
The dampness starts about 1.3 m up, next to the socket, dropping down through gravity.
The conservatory is unventilated and unheated therefore the vapour from the unvented kitchen is coming into contact with the original external wall.
There is dampness deep within the wall behind the slurry.
Often moisture blister behind the slurry see examples later in this report. The solution is humidity control through ventilation and heat balance.
There is dampness in an internal wall next to the washing machine.
Again this is liable to be condensation as there appeared to be no staining from a leak.
There is a slightly stained area of dampness just behind the kitchen sink confirmed by high damp meter reading.
On the other side of the wall under the kitchen sink there is a cold-water inlet.
Cold water comes into a property at about 8°C. The green corrosion on copper pipe suggests that condensation was forming under the kitchen sink. I suspect that either water splashing from the sink or condensation under the sink, is the root cause of this dampness in this section of the conservatory.
Calcium sulphate crystals blistering behind paint work in the external toilet.
Once dry, the plasterer can be sanded back with coarse grain sandpaper. A skim coat maybe all that is necessary to the bring the wall back to shape.
Cisterns can become very cold after flushing and refilling with cold water.
It is common to see condensation forming around a cistern in an unheated and poorly ventilated toilet.
You described how the hatch to the cellar becomes covered in condensation.
Looking in the cellar we see dribble marks on the wall and corroded pipes indicating periods of condensation.
When vapour drops below the dew point in a cellar it is liable to condense on the damp proof course (“DPC”). The DPC blocks water from becoming absorbed downwards resulting in upwards absorption in a rising damp like profile, see examples later in this report.
I tested your front-righthand rainwater down drain with a jug of water and found it to be blocked.
Moisture entering the cellar and insufficient cellar ventilation is likely to be a contributory factor resulting in rising damp like symptoms.
Upstairs there is mould on the bathroom ceiling. The extractor fan was not working.
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.
The shape of the mould suggests ventilation imbalance in the loft above, where some of the loft is well insulated and other parts are not, resulting in heat loss in the unventilated sections. Bathrooms should have extractor fan running at 15 l/s with a 30-minute overrun and rigid ducting, see surveyor.tips/vent_regs
There was damp staining to the middle bedroom wall.
Despite appearances this section of wall was dry.
The mould in the corner comes from heat loss and excess vapour possibly from tenants drying clothes.
The windows don’t have trickle vents.
A gutter outlet looks a newly installed, a piece of plastic appears to be directing water away from the wall.
It looks to me as if the gutter was leaking but has now been repaired you should look to see what happens during a rainstorm.
There is staining to the top of the chimney breast in the second bedroom.
The chimney is damp within the loft.
I felt the sarking material above the damp section of wall. It felt like debris had fallen into the sarking.
I was unable to see the flashing behind the chimney breast, which may be the root cause.
The flaunching and re-pointing of the chimney breast looks tired.
The guttering looks out of line, there is moss and the tiles may have slipped in places.
I recommend a separate roofing survey by somebody with external access to the chimney at roof level.
There is mould growing in the front corner of the master bedroom, this is from insufficient ventilation.
You were concerned about a crack in the coving.
We are not structural engineers. However, you should be more concerned about vertical cracks from a structural perspective.
There is damp staining where a chimney breast has been removed, in the back addition first floor.
The ceiling was marginally dry.
The damp area was to the right of the original chimney breast.
Looking in the loft we can see support under the chimney stack. Some of the timber is damp at risk of rot.
The iron support has rusted in places, it is possible that interstitial condensation is forming on the iron and falling onto the ceiling below.
Looking at the chimney from the neighbour’s side we see a missing brick above the area of ingress and a plant.
The neighbour’s side of the chimney breast should be rendered in a similar manner to your chimney breast. A neater, but perhaps more expensive solution is to remove the chimney breast and re-tile that area, if the chimney is no longer in use. You should take advice from a roofing surveyor and discuss the matter with your neighbour.
There is mould in the rear bedroom ceiling and what looks like a damp stain, possible from a blocked gutter.
That section of ceiling was dry at the time of the survey.
You should measure the ceiling with the damp meter after a rainstorm and look at to having and independent roofing survey (this is not a roofing survey).
A section of gutter above the downpipe appears to be blocked and should be unblocked with a gutter clearer.
Dataloggers
You send me data back from dataloggers here are a few observations and conclusions.
Other matters
Water could bounce into the cellar. You should check inside the cellar during or soon after a rainstorm.
Consider lowering the height of the external patio(s) or blocking the last layer of vent holes with silicon, while monitoring and maintaining adequate ventilation or dehumidification in the cellar.
There are various cracks to render that should be raked out and filled.
The dampness in this property is complex. Some additional issues may come to light after you have completed the recommendations.