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Know Your Wood Rotting Fungi
Know Your Wood Rotting Fungi

Know your Wood Rotting Fungi:

grc

Graham Roy Coleman.
B.Sc(Hons),M.I.Biol.,C.Biol.,A.I.W.Sc.,F.Inst.S.S.E..
Remedial Technical Services



When looking at wood rotting fungi which may be found in the average domestic environment, it is first essential to understand that WATER IS REQUIRED TO INITIATE AND SUSTAIN ROT. So whilst there is some importance to be able to distingush between dry rot , Serpula lacrymans, and the rest (wet rots), they have ALL been caused by excess water in timber! And the basic control is to eliminate the water causing the rot - dry wood doesn't rot!!

The first practical observation which should be made is to determine the nature of the rot - is it a 'brown rot' or a 'white rot'?

Brown and white rots:

Brown rots:

Brown rots cause the wood to crack in a cuboidal manner; the wood also goes slightly darker in color.
The 'cubes' may vary in size depending on the wood and conditions, but they are generally very visible and distinct especially as the wood dries.

There are many 'brown rots', dry rot (Serpula lacrymans) being just one. Thus, if the rot is identified as one of the brown rots then it could be dry rot.
brown rot
White rots:

Wood attacked by a white rot looks completely different to attack by a brown rot: The wood takes on a 'fibrous appearance and tends to go slightly lighter in color ( this may not be too noticeable). There is no cuboidal cracking as in the brown rots. Tend to be more common in hardwoods

If the damage is shown to be from one of the white rots then it is certain that the rot isn't dry rot (dry rot is a brown rot)
white rot

Once you have established the basic type of rot - brown or white, then one can start looking at the features which will help you identify the precise rot causing the damage.

You should also note that the term 'dry rot' refers to one particular organism only - Serpula lacrymans. All other rots are colelctively refered to as 'wet rots'.

Please note that the following is just a guide and will not list all the possible wood rotting fungi which may be causing a problem.

Basic structures on which recognition can be made:-

The wood:

The basic nature of the rot will cause the wood to break into cuboidal cracks (brown rots) or take on a very coarse fibrous appearance (white rots). However, it is also useful to know whether the wood is a hardwood or a softwood as some rots will only attack one or the other.

The fruiting body:

This is the 'mushroom' stage of the rot, ie, the reproductive stage. If there is a fruiting body then, in general terms, it is much easier to identify the rot. Unfortunately one can find atypical forms of fruiting bodies.

The mycelium:

This is the 'body' of the growth and consists of masses of very fine filaments (hyphae). It is the mycelium which secretes the enzymes, special chemicals, which break down the wood components into much simpler materials, ie, simple sugars, which the fungus can use for nutrition, growth and survival.

Strands:

Some rots form 'strands' which are effectively a group of thick walled hyphae. There function is to transmit 'food' (breakdown products of wood) to the growing mass.

 

Brown rots:



Dry rot (Serpula lacrymans):

Almost certainly the most 'feared' of the rots, and sometimes called the 'cancer of a house'. However, like ALL wood rotting fungi, it requires water to become initiated, to grow and survive.

Dry rot is restricted to damp humid conditions; this makes it sometimes very difficult to find.

Dry rot has the ability to grow over and through materials from which it gains no nutritional value, eg, soil, plaster, mortar. BUT IT CAN ONLY DO THIS EFFECTIVELY IF SUCH MATERIALS ARE DAMP - IT WILL NOT GROW OVER AND THROUGH GENUINELY DRY MATERIALS!!. Thus, if there is dry rot in, say, flooring timbers it will not grow up through the masonry of the walls and effectively rot the rest of the house if such walls are dry.

So what are the points one should look for?
 
 
Serpula lacrymans spores
 The wood:

Typical cuboidal cracking of a brown rot, sometimes the cubes being quite large. Prefers softwoods to hardwoods.
 
dry rot

The fruiting body:

Typically a 'pan-cake' or bracket, quite fleshy with an outer white margin. The surface within the margin is a rust red color and consists of large pores.

The fruiting body or indeed an area where fruiting bodies exist may be covered with a fine rust red colored 'dust' - these are the millions of spores ejected by the fruiting body. However, nothing will happen to these spores unless they are on a suitable and damp substrate, ie, damp wood. If they land on dry wood then nothing whatsoever will happen provided the wood stays dry - remember dry rot requires water to initiate, grow and survive; dry wood doesn't rot!!.
 
Fruiting body

The mycelium:

This is effectively the main body of the fungus and is often present in sufficient quantity to be visible.

It may take on several forms depending on the conditions.

Points to look for:

1. White fluffy cotton wool-like growth; usually found under humid conditions. Under some relatively rare very damp conditions droplets of water may be seen on the growth.

2. A 'skin-like' growth, usually fairly flat. May be a 'mushroom' color of a silvery-grey skin. Both can sometimes be tinged with patches of lilac or yellow coloration. These skins peel like a mushroom head.

3. Distinct thick tubular-like growth (strands) which may be up to 3mm diameter, but often smaller. Usually gray in color and embedded in the mycelium in which they develop; can sometimes be found on their own. When dried they become brittle and distinctly crack when bent, ie, they are brittle when dry. Strands are capable of growing over and through DAMP materials, and it is these structures that allow the rot effectively to spread from timber to timber via the damp substrate: it is the strands that make dry rot so potentially dangerous.

1.

 

 

 

 

2.

mycelium 2

 

3. strands:

strands

 

The Cellar fungus (Coniophora puteana):

The most common rot found in properties (Coniophora marmorata looks the same).

Frequently associated with timbers in contact with damp masonry, the masonry just being damp (capillary bound water) rather than a distinct source of water ingress as for dry rot. Hence it is very common in skirtings agaisnt a wall affected by rising damp, built-in floor joist ends and also in timbers subject to long term severe condensation.

So points to look for:

The wood:

Typical cuboidal cracking as for all brown rots; the 'cubes', however, are usually found to be smaller than for dry rot.

On interesting feature of the fungus is that the wood is often decayed internally, a very thin surface veneer of sound timber being left. Where it occurs in timbers subject, for example, to subfloor condensation the surface may appear slighly concave due to the internal rot causing the wood to shrink.
cp wood
The fruiting body:

Reported not to be common so it may not be found.

Usually a thin tough flat olive brown plate with small lumps on the surface. May have a pinkish-white margin.
cp fruiting body
The mycelium:

Not always present so there may be occassions where this rot may be difficult to distinguish from dry rot.

The mycelium usually develops under more humid conditions so, for example, it might be found on the back of a skirting fixed to a damp wall. In its early stages it appears white but usually when found it is olive brown to black, sometimes quite thin and other times in distinct sheets.

This fungus also produces strands which can also move over VERY DAMP inert materials, but do not pose the problem like dry rot. Unlike the strands of dry rot, cellar fungus strands are usually fine with no real strength; usually brown or black in color. Often seen emanating from infected wood
cp mycelium

cp strands

 

The Mine fungus (Antrodia vaillantii -
formerly Fibroporia vaillantii) - a wet rot


Far less common than the Cellar fungus and Dry rot, which probably consititute over 90% of rots found in the domestic environment. Attacks softwoods.

A wet rot causing typical cuboidal cracking, the cracks breaking the surface; it is often misidentified as dry rot.
 
The wood:

Typical brown rot damage - cuboidal cracking, the cracks readily being viewed on the surface like dry rot.

If there is no mycelium then it will be very difficult to recognise
 Antrodia attack
 The fruiting body:

Usually easy to identify, it is somewhat fleshy, up to around 12mm in thickness, and is pure white but sometimes seen with a tinge of orange color. However, the most striking feature is that the surface has a 'honeycombed' appearance when viewed from above; the opening to the pores are angular and small (2 - 4 to the mm).
fruiting body
The mycelium:

Where present it takes on a 'fern-like' appearance, rather like frost fanning out on a window. Again, like the fruiting body, it is pure white.

The fungus also produces strands: these are what usually lead to a misidentification, the fungus often being confused with dry rot. However, there are 2 big differences, (1) Antrodia strands are flexible when dry (c/f. dry rot), and (2) they are usually pure white.
mycelium

 

 

 

WHITE ROTS:

 

Phellinus contiguus - a wet rot:

Phellinus is probably one of the most common white rots found in buildings. Indeed, it caused significant problems in softwood window and door joinery in houses built in the 1950's and '60's.

Attacks both softwood and hardwoods
 
The wood:

Typical white rot damage, the wood breaking down into very coarse fibres, slightly bleached in color.

Frequently tufts of the tawny colored mycelium can be seen in the cracks of the decaying wood (see below)
phellinus

The fruiting body:

Phellinus forms a dark brown, hard 'woody' fruiting body, often quite thin, and remains on the wood.

It appears somewhat like looking at the end of rolled up very fine corrugated paper when viewed from the top, ie, it has very fine irregular shaped pores.

If a section of the fruiting body is viewed under a microscope you might see dark 'hairs' (setae) protruding into the pores.
phel fb
The mycelium:

May form tawny colored sheets which remain on the wood. However, it is more likely that one will see tawny 'tufts' of the mycelium between the cracks in the fibrousy rotted wood (see arrow).

There are no strands.
 
phelinus tufts

 

 

Asterostroma spp - a wet rot

There are several species of Asterostroma to be found.

Attacks softwoods, probabaly where conditions are quite damp. The samples in the photos were obtained from a leaking flat roof.
 
The wood:

Attacks softwoods. The surface takes on what can only be described as a 'weathered' appearance with the wood rotting like that of a typical white rot. However, the wood does not appear to crumble when rubbed between the fingers - remains somewhat more 'together'.
 
The fruiting body:

Not readily distinguishable from the mycelium (see below). There are no obvious pores
growth
The mycelium:

Forms flat sheets of a grey to pinkish-grey growth over the timbers, the sheets being very flat. Asterostroma is very easy to identify if you have a microscope since the mycelium contains masses of tiny pointed star-shaped structures (hence the name 'astero' - star; 'stroma' - body)

Asterostroma also produces strands (see fine strands in top photo); these are usually vey find and quite strong. They will run over wood and damp masonry for quite some distance.

asterostroma