Module 5 · Biological Agents
5.1 Mould, and What Its Pattern Tells You
9 min read
Mould is treated as the problem, and it is a symptom — one that happens to be an unusually informative one. It grows where water activity at a surface is high enough for long enough, and because that is governed by surface temperature, a mould pattern is a readable map of a building's thermal weaknesses. A practitioner who photographs the pattern and works out what it is mapping has learned more than one who sends a sample to a laboratory.
Learning objectives
By the end of this lesson you will be able to:
- State the conditions mould requires and the timescales involved.
- Read a growth pattern as a map of surface temperature and air movement.
- Explain why species identification rarely changes the remediation.
- Distinguish a building-driven pattern from an occupancy-driven one.
Key terms
- Water activity
- The availability of water to an organism at a surface, effectively the relative humidity in the boundary layer against it. What mould responds to, rather than the room humidity.
- Xerophilic
- Tolerant of low water availability. The first colonisers on a marginally damp surface are xerophilic species that establish where wetter-loving ones cannot.
- Succession
- The sequence of species colonising a surface as it gets wetter or stays wet longer. Why a mature growth looks different from a new one.
- Thermal bridge
- A path of higher conductivity through the fabric, producing a locally cold internal surface — lintels, jambs, junctions, structural elements, wall-to-floor corners.
Read the rest of Biological Agents
Module 1 is open to everyone. The remaining six modules — building science, each damp mechanism in depth, meters and thermal imaging, the full inspection method, and report writing — are free too. We just ask for an email so you can pick up where you left off, and so we can send your certificate when you finish.