Background
The issue has developed over several years. While it is not severe, progress needs to be halted to allow for the bathroom to be repaired, the appearance to be improved, and the integrity of the wall to be ensured for the future.
Data loggers – see damp.ai/detect

Conclusion from data loggers
The data logger support there theory that excess vapour is the cause of the dampness and mould and the base of the toilet wall.
Evidence & Illustrations

To keep the property dry | |
|---|---|
| Remove mould | |
| Consider sanding down mould where dry, and removing it with either bleach or anti-mould foam. I personally use HG Mould Remover Foam Spray, though other reputable brands should provide similar results. | £20 |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | |
| Bathroom Humidity Management | |
| After showering, keep the bathroom door closed and the window open to allow vapour to dissipate. I would install a bathroom extractor fan, that vent straight out. It should run at least 15 litres per second, with a 30 minute overrun set up when installed. The cost is about £400 – £800 depending on electrical supply – which you should already have. | |
| Follow Dew’s Law | |
| Follow Dew’s Law to effectively manage internal vapour, it is crucial to maintain the internal vapour levels, as measured by the dew point in degrees Centigrade, below the external temperature. This can be achieved through adequate ventilation and the use of dehumidifiers. Monitor the internal Dew Point with a reliable device, such as the Habotest Hygrometer or Dew Point Meter HT607, or utilise the sensorblue app paired with the ORIA Wireless Thermometer Hygrometer. These tools help in accurately gauging humidity levels, ensuring they remain optimal. For more detailed information on detecting and managing damp issues, please visit https://damp.ai/detect. | |
| Use a dehumidifier | |
| Maintain relative humidity, especially at night when it’s cold outside, with a dehumidifier such as PureMate 20L/Day Portable & Compact Dehumidifier with 6.5 Litre (£179.99 Refrigerant), Duux Bora Smart Dehumidifier (DXDH02UK £300 Refrigerant) or Meaco DD8L Zambezi (£260 Desiccant – best for colder environments) – Which! Best buys. There are plenty of alternatives available. I choose a dehumidifier based on daily and tank capacity, low noise, whether it has a pipe out, and ease of programmable functions over other considerations such as weight and aesthetics. The technology is old and easy to manufacture. So if these brands are not available, you are sure to find another alternative. Evaluate based on daily capacity (20L minimum) and whether it has a continuous pipe out (use this to drip into a sink when away in winter). | £180 |
| Cooking Tips | |
| Always cook with tops on pots and pans to reduce vapour emission by 80% and ideally keep the door closed to the rest of the house. Or better still, install and use an externally ducted kitchen extractor fan – cost about £200 – £300 to duct it out. | |
| Maintain airflow close to cold walls | |
| TIP: Keep objects away from walls where condensation or mould has built up. Consider insulating cold internal surfaces, for example, with floor insulation from B&Q or Wallrock Thermal Liner (ensure to use Wallrock Thermal Liner Adhesive). | |
| Remedial actions – estimate of costs | £200 |
