What is wood rot?

Fungi advance over the surface of the wood and excrete enzymes as they go. These break down the wood structure and nutrients are absorbed by the mycelium.

There are two main types of wood Rot

Dry Rot and Wet Rot is often given as the answer.

But the correct answer is really Brown rot and White rot.

Brown rots

  • These include True Dry Rot, Mine Fungus, and Cellar Fungus, the three common fungi we deal with.
  • These fungi secrete the enzyme cellulase which breaks down the cellulose and hemicellulose in the cells.
  • The timber turns brown and cracks cuboidally.
  • If the decayed timber is not brown it can’t be True Dry Rot.

White rots

  • These include Asterostroma spp, Donkioporia expansa and Phellinus contiguus
  • These fungi secrete the enzymes lignase and cellulase and attack all the components of wood, cellulose, hemicellulose and the lignin
  • The timber is bleached and becomes fibrous
  • Chemical attack can be mistaken for White rot as the timber will become fibrous when subjected to acids and alkalis.

Life cycle of wood rot:-

Spores

Spores germinate

Hyphae

Mycelium

Sporophore

 

True Dry Rot (Serpula lacrymans)

Damp, poorly ventilated timber. Often softwood timber which is hidden from view.

Prefers damp (>20% moisture) and not wet timber. It rarely affects wood outdoors. It is not normally associated with rising damp.

Optimum temperature is 22°C (max 26°C) and 30- 40% moisture content

(Fibre saturation point).

25-33% of spores are viable. But can survive desiccation for several They look like red dust, are 0.01mm long. 20000M/square metre.

 

Musty, mushroom-like smell, with lots of mycelium.

In humid still conditions forms fluffy cotton wool like growth with lilac and yellow tinges.

Once the fungus has taken hold a mass of cottony threads develop then long root-like strands appear seeking out fresh wood. These strands can pass through masonry and survive 1 year at 20c or 9 years at 7.5c. They may extract calcium from the masonry and are BRITTLE when dry.

When activated by light, multiple pancake-shaped fruiting bodies are formed on timbers or plaster.

 

 

Wet rots

Wet rots are a group of fungi which decay timber in the presence of higher levels of moisture than those necessary for Dry rot.

The causes often provide continuous damp, such as rising damp, poor subfloor ventilation, the failure or lack of DPMs, debris below the floor and slow undetected plumbing leaks.

Wet rot damage is limited to the timber although the original water ingress problem may also cause other areas to be affected by damp (such as plaster & decorations).

Generally, with wet rot, there is less mycelium and sporophores can be rare.

 

Cellar fungus (Coniophora puteana)

  • Affected timbers often have a thin sound skin concealing longitudinal cracking with some cuboidal cracking.
  • Decay appears to be darker than the surrounding timber.
  • Mycelial growth is uncommon but when found is brown and fernlike.
  • Optimum temperature is 23°C and 50-60% moisture content.

 

Mine fungus (Fibroporia vaillantii)

  • Poria species – Note pores in sporophore
  • Affected timbers often have a thin sound skin concealing longitudinal cracking with some cuboidal cracking.
  • Strands white and FLEXIBLE. Can grow across masonry.
  • Mycelial growth is white and fernlike.
  • Optimum temperature is 27°C (max 36ºC) and 40-50% moisture content

 

Other Wet rot species

There are ‘hundreds’ of wet rots in the UK. These are often the mushrooms and toadstool’s we see in woodland.

Their spores can enter properties and germinate. Environmental conditions can dramatically change what they look like.

Identification is often not easy and for the purposes of control, usually not important.

 

Plaster fungus – Elf Cup (Peziza sp). This is not a wood rotting fungi, however, its presence indicates

saturated plaster or masonry

The challenge is to dry without encouraging true dry rot.

 

 

 

 

 

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