Dry Rot, what it is and how it starts
How Dry Rot (Serpula lacrymans) starts and develops
Dry Rot fungal spores are omnipresent and these are widely dispersed by air currents. If a spore falls on untreated damp wood they will germinate by pushing out a hollow tube called a hypha which grows and branches to form a mass of hyphal threads called mycelium. Mycelium develops inside the timber and breaks down the wood for food.
The mycelium of Serpula lacrymans develops extensively on the surface of infected timber and in still, humid conditions produces a mass of cotton wool-like growth. Water droplets are often produced on the surface of the mycelium and this feature has given the fungus its name ‘lacrymans’ (from the latin ‘tears’). Bright lemon-yellow patches may also be seen, but these are more common, together with tinges of lilac, in less humid situations where the surface mycelium is reduced to a thin silken skin.
Mycelium spreads over the timber surface by the continued growth and branching of the delicate hyphal threads at the growing with time. Specialised strands develop within the mycelium and these supply water and nutrients to the growing front with time. The strands assume their real significance when the fungus spreads from infected timber onto the surface of adjacent stone or brick walls. The tiny hyphal threads penetrate the mortar joints and plaster layers and large areas of damp wall can then become infected. The fungus cannot derive any nourishment from the wall materials (although it is thought that calcium salts in such materials contribute to the success of the fungus in such situations) and the strands, which have thick walls and are resistant to moisture loss, are able to continue to supply water and food to the growing front for considerable periods of time. The mycelium in which the strand originally developed often breaks down. In such cases, the strands alone link the food source (decaying wood) and the hyphae at the growing front and remain as the only evidence of fungal growth in the wall.
In the past, it had been thought that the fungus often wetted previously dry areas to allow further spread, but it has recently been recognised that this happens only infrequently. In most instances, the fungus is restricted to areas where both timbers and walls are damp. It should be remembered, however, that the most careful examination of a building found to be suffering from dry rot must be made as the extent of dampness may not be clear. The full extent of spread of the fungus must be determined before remedial treatment can be undertaken confidently.
There is so much conflicting information available on the internet. Supposed “industry experts” show pictures of dry rot on their sites, but it is clearly wet rot, and vice versa. These experts state that; wet rot means wet timber, not always true; that wet rot hyphae (strands) are dark in colour, not always true.
Identifying wet root can be tough, but you should always err on the side of caution. If you have any doubt that the rot you have is not wet rot but dry-rot, then treat as dry rot. Dry rot has far greater virulence and can do a lot more damage to the structural integrity of your home.