Dry Rot

This is not intended to be a technical discussion on dry rot.  There are other documents on the Internet that describe this organism in far more detail; and this link will transport you to a perfect example.  I’m just trying to shed a little light on a topic that doesn’t seem to be discussed at dinner parties; and once again, the aim is to familiarise you with the problem so that if it happens to you, you don’t spend your inheritance unnecessarily:

The less we know of something, the more it seems we’re frightened of it, and that’s certainly the case with Dry Rot or, as the upper classes refer to it,  Serpula Lacrymans.

When people ask me if they have it in their home, they often do so with hushed voices and narrowed eyes; as though floating the question sotto voce would somehow keep it at bay.  I should think the denizens of plague-infected villages must have adopted a similar tone when enquiring after their neighbour’s health.

Well, as with all things mysterious, once we have an insight into its nucleus, it doesn’t seem quite so bad.  However, a word of warning: this is definitely not a rot that can be treated with disdain; but equally, neither is there a need to sell the house, nor practice incantations to the Wood Sprites.

Firstly: its name is somewhat inappropriate. Dry Rot doesn’t actually do ‘Dry’. If there’s one thing it needs – well two actually – it’s moisture and food; and if either of these commodities are removed, it dies.  Not immediately, but with a certain finality nevertheless.

So, first thing to remember: if the timber you’re worried about is dry, then it won’t be suffering from ‘Dry Rot’.  However, if the timber is wet, and here we’re talking about moisture content in the region of  28 - 35%, then ‘Dry Rot’ is certainly a possibility; and if the timber in question is also in a dark, airless environment, the probability factor rises exponentially.

To put that into perspective.  The average moisture content of exposed timbers – such as architraves or skirting boards etc, in a well-ventilated property, will usually be in the region of 6 – 14%, sometimes a little higher, depending on individual circumstances. 

To achieve moisture content that will allow the organism to instigate, the timber will have had to become pretty wet. The ‘if you touched it, you’d know it was wet’ sort of wet, which can be caused by such things as plumbing leaks, leaking gutters or severe penetrating dampness etc..  In some cases, contact with damp masonry, resulting from failed damp proofing courses can also allow it to start, but this is uncommon – rising dampness does not often result in dry rot.

In addition to the requirement of high moisture content in the host timber, poor ventilation in its surrounding environment is also a common feature; and such conditions often occur in dark, out of the way places, like sub-floors, behind panelling or in little-used cellars etc. Its preference for these habitats often makes it difficult to see until it has caused considerable damage.

Good ventilation interferes with the organism’s ability to spread, and thus it’s seldom seen in well-lit, airy places; and virtually never outside in the open air. If it does show itself where light and air are in abundance, this is often in the form of a fruiting body, and can often mean the organism is struggling for survival.  The fruiting body enables it to propagate its spores so that it can continue its life cycle somewhere else. But that’s another story.

Perhaps the main reason this fungus is so feared is because of its ability to spread with commendable rapidity; other rots generally do not have this gift; they are slow growing and relatively meek in comparison.  Given enough time, common ‘wet’ rots will also render timber structurally unsound but the damage they cause is usually confined by their slow progression into other areas of  timber that share a high moisture content.

If wet rot encounters timber with marginal moisture content of  20 – 22%, its growth will slow to the point of ineffectuality, or it may even become dormant. Not so Dry Rot, which can infect similar timbers many centimetres, or even metres, from its source. It does this by producing clearly visible, ‘tentacle’ like growths known as ‘strands’. These spread out and provide nutrients to the ‘coal face’, where small structures known as Hyphae work with Stakhanovite vigour to break down the timber itself.  When this process of breaking down occurs, moisture is produced as a by-product, and the process is further enabled: the rot goes on. 

To make matters worse, these strands can grow through masonry walls, or insinuate themselves behind plaster, although these suh-structures have to be damp, and the fungus does not derive nutrition from them.  This method of advancement makes it totally different to the other common rots.

What does it look like…

It depends on its environment.  In very humid conditions, it can look like a collection of cotton wool balls, which sometimes develop drops of liquid upon them, thus giving rise to the name Lacrymans.  When conditions aren’t so humid, its mycelium, which is the coagulation of the hyphael growth, resembles the outer skin of a mushroom.  It’s quite silky to the touch and sometimes has yellowish or purple patches upon it.  If you can get over your horror of its purpose, it could be considered quite attractive.  Not surprisingly, as it looks like a mushroom, it also smells like one.

Timber, that is, or has been, the host to this organism is altered considerably, both in its appearance and its structural qualities.  Where it was once strong and appealing in nature, it becomes brownish in colour and develops an unmistakable cuboid appearance, i.e. it’s consistency changes to that of small cubes of timber, separated around their perimeters by jagged fissures.  Furthermore, it now has the strength of a newborn chicken and the consistency of charcoal.  As support for a roof, or the floor above, it’s pants. 

Other ‘brown’ rots, so called because they only attack the cellulose of the timber and leave the brownish coloured lignin behind, also create a cuboidal condition but these often leave an outer skin, which is superficially untouched.  Dry rot doesn’t do this; it starts from the outside and goes all the way in. The cubes are also usually bigger in size.

So, what to do about it…

Well, I think it is probably unlikely that anyone not familiar with this organism is gong to attempt to cure it, especially as ‘opening up’ of masonry or floors etc is very often required. I don’t think this is the forum for treatment analysis, the aim of this short article is to familiarise you with it and hopefully, stop you being frightened to death!

However, and as mentioned somewhere near the beginning, this rot is no different to any other in that it needs sustenance and moisture.  Remove either of these and the rot will die. From this it follows that whoever you ask to treat it must ensure that any sources of moisture are eliminated.  Depending on how far the rot has managed to travel, and how easy it is to dry the affected timbers, this may be the only form of treatment required. However, in practice it may sometimes be necessary to enlist the aid of fungicides too.

But be careful if anyone wants to irrigate masonry by injecting the walls with biocides. Due to the difficulty of dispersing these adequately, their effect is questionable and they deposit a large amount of water, which can cause more problems than it cures. This smacks of the 'throw everything at it' approach to me and you might want to consider a more thoughtful strategy.

You should ensure that whoever deals with the rot is familiar with the problems it can create; it isn’t always a simple rot to deal with.  If you have a period property, or it's listed, you should employ someone who sympathises with the building; extensive cutting out and burning may not be an option in such cases, particularly if the timber is supporting panels or decorative plasterwork.  In such cases, drying out, patience and on-going monitoring are required.  This approach may not suit some contractors who want to be ‘done and dusted’ by five o’clock.

Whatever, just remember that this rot is no different to any other in its requirements, it isn’t ‘Super Rot’, and depriving it of its basic needs will ensure its demise.

So that it doesn’t even got a toe-hold, make sure that that leaking gutter is repaired and the drip behind the washing machine is dealt with sooner rather than later.  You could be kicking yourself if you don’t.