Dry rot (or true dry rot) in timber is caused by the brown wood rotting fungus called Serpula Lacrymans. It is a major cause of timber rot within buildings. Its name describes the condition at the end of the infection, also the timber (mostly softwood) must be wet >28%MC for it to occur. But once established it can survive in lower moisture levels 20% in pine timber or 18% in some spruce, which is lower than other brown wood rotting fungus. It is important to remember, there is nothing dry about dry rot.
Research in the mid 90’s at the University of Abertay by Pro J W Palfreyman found that there are other Fungi, which will attack Serpula Lacrymans.
In its early stage you will not see any visible sights of decay. But once the hypha has consumed the lignin within the wood, which helps to form the support structure of wood, you will then see large brown cuboid damage.
It is only associated with pore building maintenance. Even with a damp environment it does not always germinate.
The spore is the asexual reproductive method of the dry rot fungus and can survive for up to 2 years. Ridout B. (2000) “Timber Decay in Buildings.
These are small filaments which grow from the spore and infect the timber, as a mass they make a mycelium. The colonisation requires a suitable amount of water in the wood normally 28-30% Moisture content and will colonise rapidly at 22oC. It prefers dark and poorly vented humid areas >80%RH.
They are grey when older and white when fresh.
The presence of alkali minerals in masonry (lime mortar) assists the fungus to continue the decay of the timber.
(Bench-Anderson, 1985; Palfreyman, 1996).
They are often the first sign a building owner sees of a dry rot outbreak. In layman’s terms it is the flower of the fungus and produces spores instead of pollen. The red dusty material ejected from a fruiting bodie is the spores.
Once the timber and masonry around it starts to dry out quickly, the rot will become dormant and eventually die. The length of time that the fungus can remain dormant under dry conditions seems to depend on the temperature, with approximate times of 9 years at 7.5 C and 1 year at 22 C being quoted.
By the BRE and Ridout B. (2000) “Timber Decay in Buildings.
I have seen some dry rot infections, which have stopped and started over a 50-year period. This is due to the damage done to the timbers, which reduces the timbers natural durability against infection once it becomes wet. I can become dormant for 1-9 years depending on the ambient temperature of the building.
Total irrigation of open brick work or a masonry wall has not been best practice since 1985 ref BRE Digest 299. It can be helpful in some cases to create a cordon sanitaire around an area.
Locate the sources of moisture and promote rapid drying.
Find the extent of the outbreak.
Remove the rotten timber.
Disinfect the masonry.
Reinstate with timber treated with a suitable preservative or durable timbers.
Carry out structural repairs, as necessary.