Mould is a term used to describe fungus that can appear as a white coloured furry or filamentous growth. Mould is actually a complex group of organisms which are neither plant or animal, but which obtain their food from living or dead material.
Mildew is a term used for fluffy white growth commonly found on textiles
Foxing refers brown spots found on paper sometimes caused by mould
How does it grow?
Mould begins life as a spore (comparable to seeds in the plant kingdom). Spores are minuscule and are ever present in the air around us. In very humid air, the concentration of spores is much higher.
Because of their tiny size, they are carried by air currents and only settle on surfaces in very still air. They may stay dormant for long periods of time, waiting for favourable conditions in order to germinate
Once germinated, the mould produces string-like filaments known as hyphae. This is the growing stage of the mould. When many hyphae come together, the mass is known as mycelium, the visible part of the mould which can produce and release spores into the air to start new colonies.
What conditions does mould grow in?
- Relative humidity (RH) at 65% or above.
- Temperatures between 10 and 35°C.
- Prefers dark spaces.
- Requires a food source – this may be the object itself, particularly when made of organic materials, or the organic dirt on the surface of an object.
What damage can be caused?
- Can be extremely harmful to health and precautions should always be taken when dealing with mould i.e. gloves and a face mask.
- Mould will break down materials both chemically and physically causing brittleness and staining
Monitoring mould growth
Mould growth is usually monitored by visual inspection as it is visible to the human eye. Raking light is a useful tool to use to make inspection easier. UV light can also be used as mould will fluoresce under UV light.
Mould will grow in dark, damp spaces so it is important to monitor areas where these conditions exist e.g. behind pictures, inside furniture, by cold external walls and in damp cellars.
Controlling mould growth
- Keep RH levels below 65%
- Provide good ventilation and air circulation
- Keep dust levels to a minimum
- Regular inspections and monitoring of RH
Treatment of mould
The use of fungicides or fumigants to treat affected objects is not recommended as it may only offer temporary results. The chemicals used in such products are often toxic and have the potential to cause further damage to objects.
If a mould outbreak is discovered:
- Isolate the affected material in a clear sealed polythene bag and seek specialist conservation advice
- Discard any storage materials that have been in contact with the object
- Use cool air to dry out the material if it is damp. Warm air will encourage further growth
- In an emergency the material may be frozen until further treatment can be arranged
- Find out the cause of the outbreak (usually moisture ingress)
Removal of mould
- Assume there is a health hazard
- Wear a dust mask (category FFP3) and disposable nitrile gloves
- Ensure that the object and the mould has been dried out by either moving it to a drier environment or using a cold air fan
- Do not attempt to remove mould from any surface that has a loose, fragile or friable surface
- Check first that the mould is dormant. It it smears across the surface it means that it is still active and needs to dry out further. If it brushes off easily then you can proceed with removing it
- Gently remove loose mould from the surface with a soft brush into a vacuum cleaner fitted with HEPA filters. Always carry out in a well-ventilated space.
- The surface may be further cleaned by lightly swabbing with surgical spirit but it is advised to seek specialist advice from a conservator first