104X: Rising damp treatment questioned, why?

Owners questioned damp proofer’s half-way through work.

Surveyor Tips:

• If there is no rising damp, then plaster should not be replaced.
• The root cause should be dealt with.

Root cause

Illustrations

2020

There is discolouration to the front wall. A film was put over the airbrick causing heat loss without ventilation.

The tenants were drying clothes in the front room whilst blocking airflow.

2021

The wall and discolouration has not changed significantly since 2020.

2020

Shingles to the front were causing water to enter into the sub-floor. I moved the shingles back from the vents.

2021

The render plinth has been hacked off, chemicals injected, and sub-floor vents replaced.

Rising damp is from walls absorbing groundwater, i.e. the water under the water table: the risk is remote as:

• The soil below is “Rocks with essentially no groundwater” see the Geological survey.
• The property is on a hill, see flood risk
• Groundwater in pumped out of the ground in London, see information discussing a depth of 100M in 1980’s to about 40M now.

2021

The windowsills have been sealed up, which looks good.

2021

The builders should confirm that they plan to seal all remaining gaps, such as visible here.

The timber should be stripped, sanded down and repainted to reduce the risk of window rot.

2021

The sub-floor relative humidity is 65%RH which is normal, confirming that there is no rising damp.

2021

The dampness to the kitchen in 2020 was believed to be caused by poor ventilation or a leaking heating system.

2021

Since I improved bathroom ventilation last year, humidity from the bathroom is no longer likely to be a factor.

2021

Dampness is detectable high up on the wall. This could be from showering or a neighbour.

2021

Surface salts are visible on the ceiling. I tried to access the flat above and the side, neither where occupied.

2021

The external tap leaks when it is running. I could not test for pressure loss from the mains.

2021

The sub-floor relative humidity to the rear is also low.

Conclusion from a process of improving obvious defects first and elimination:

1) rising damp is unlikely,

2) current rot is unlikely,

3) significant ongoing leak is unlikely,

4) since the vent was repaired in 2020, condensation is less likely on this wall (but can never be eliminated without supporting data),

All evidence points to a slow heating system leak as the most likely cause,

2020

2021

The heating system has lost water pressure since 2020 suggesting a leak, is it topped up during winter?

Questions

1. The bay window in the sitting room – although this has now had a chemical DPC injection process
2. The reveal of the bathroom window
3. The internal wall between the kitchen and bathroom – this is very bad
4. The external wall to the left of the kitchen door that leads to the garden
5. The cellar, now it is empty and all areas are easily visible

Answers and Actions

1. The bay window in the sitting room.
   
   Chemical damp proofing using silane, siloxane or similar is used to stop rising damp. Hopefully damage caused by hacking off the render and drilling holes is minimal.

Actions;

• 1. Make sure you have a party wall agreement with the freeholder (if you don’t own it).
  2. Make sure the builders seal-up all the cracks and gaps, put back the render plinth, probably cement based, and ensure rainwater run off with a fillet skirting made of a similar mortar to the render.
  3. Make sure that water drains away from the building, you may need an Aco drain, properly draining away.
  4. Ideally ask the builder to replace the airbricks with plastic ones as they allow much greater airflow than the porcelain ones. This is less important as there is no evidence of rising damp.
  5. I would not keep the above ground level front airbricks in the reception. They clearly annoy tenants (hence being blocked by cellophane) and are of minimal benefit unless there external airflow. In place I would have trickle vents drilled into the reception window and a continous flow bathroom extractor fan – see later (recommended to most landlords).
  6. I would make sure your builder does not replace internal plaster in the reception as:
  7. There is no evidence of rising damp,
  8. Water can become trapped behind slurry causing damage at the interface, leaving an unsightly line of salts and discolouration at the top of the slurry. Slurry also reduces a wall’s ability to absorb vapour, increasing the risk to untreated walls.

1. The reveal of the bathroom window.

When I surveyed last year, I believed that this damp reveal was caused by condensation as the bathroom fan was ineffective, so I fixed the bathroom extractor fan so that it now runs above Building Reg. requirements and for 30 minutes. If the fan was kept running and the property heated as it should have been, then the wall should have at least partially dried out since last July. However, the reveal is still damp. Dampness on the shower wall up to the ceiling suggests that the issue is compounded by another source, either from a neighbour or the shower. I tried visiting the flat above and to the side, but the occupiers were not at home.

Actions:

1. I would monitor humidity and temperature against wall or ceiling, to monitor humidity such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) – see surveyor.tips/datalogger. Or with a Govee datalogger (£42) if you need remote monitoring via WIFI.
2. Consider installing an Elta Mori, dMEV see https://surveyor.tips/extractor. If you have a continous flow fan, I would also put a clothes drying rack in the bathroom and ask tenants to dry clothes there.
3. I suggest you ask to gain access immediately above and possibly left-hand side, to see if there is a leak or poor use of grout or sealant.
4. The internal wall between the kitchen and bathroom

I believed that this was either condensation or a heating system leak. I now believe a heating system leak is more likely.

Action: Instruct a competent plumber or heating engineer to test, trace and repair leak.

1. The external wall to the left of the kitchen door that leads to the garden.

Action: This is likely to be caused by the central heating system leak, probably coupled with insufficient use of kitchen ventilation.

1. The cellar, now it is empty and all areas are easily visible

The cellar walls are normal dryness for a London Victorian property. Cellars were built to allow moisture from rain to evaporate out through sub-floor vents.

Unfortunately the walls have been covered in a moisture retaining coating that water is trying to break through from in places. It would be better to remove the coating and allow air to evaporate away, but the benefit hardly justifies the cost, in my humble opinion. It could be tidied up by carefully removing flacking masonry every so often.

Some people use “StormDry masonry protection cream” made by safeguard. I think it’s similar to the Silane/Siloxane Thixotropic cream used by most damp proofers – see instructions/Safeguards website. I understand that it is designed to stabilise brick, allowing evaporation while reducing absorption. I wouldn’t use it myself.

Limitations

This action list is provided to help the owner of the property as a courtesy, without payment or benefit from recommended actions and therefore without accepting any responsibly.