Timber Wise – Dry Rot Questions & Answer Series
Timber Can Last Indefinitely
Submerged or dry, timber can last indefinitely. Pure wood itself is not easy to destroy by the ordinary or typical operations of nature. It takes several atmospheric conditions working with each other to bring about decay. The greatest possibility of harm to trees is not moisture in and of itself. Trees flooded and submerged underwater for well over one hundred years ago have been raised from underwater as good as new. The water in lakes and rivers are in most cases too cold with insufficient oxygen to cause it to degrade. The logs retrieved from lakes are processed through conventional mills and are air or kiln dried. Although the drowned logs have faded in some cases testing shows they contain the virtual properties and quality of the best certified modern timber.
Debunking Misconceptions
Timber has centuries old misconceptions long ago debunked that are still being presented as “facts”. They seem to continue on like apologues such as birds will abandon their babies if you touch them leaving your scent; even though it has been proven that birds do not smell and will not abandon a baby bird so readily; or old wavy windows are wavy because the glass is liquid and flows down over the course of time when in fact glass is a solid amorphous; old glass didn’t become wavy over time, it was like that when it was new. With timber, it takes exacting and extreme long-term atmospheric conditions to bring about decay or invite wood destroying organisms.
One of the apologues concerning timber began in 1815 with Ralph Dodd when he published a book he titled Practical Observations on Dry Rot in Timber to advertise and peddle a product he concocted called Dry Rot Preventative. Dodd took great pains emphasizing how extremely difficult it was to get rid of dry rot and made exaggerated statements to the effect that dry rot was almost impossible to stop and that you might as well “spread flames on a wall of pitch than to stop it once this destructive Dry Rot takes place”. In conditions where Dodd discovered dry rot such as on dark, dank ships his conclusions did have partial merit as it was the common practice in that day to cover floor timbers with oiled floor cloth creating an atmosphere more conducive to dry rot spores. Unfortunately this kind of misinformation has continued to stay with us. In practical building conditions Dodd’s supposition about dry rot are not relevant.
Wood Destroying Organisms
There has been much confusion as to this destructive fungus referred to as dry rot. Dry rot is Serpula lacrymans, a fungus that germinates from a spore just as fruit or vegetation grows from a seed. The spore has to be present and posit with a moisture content saturated to the point of about 28 to 30% and the humidity to be above 95 to 98% for dry rot to begin to germinate. Even in situations where walls have had high moisture content and humidity, if the wall starts to dry, dry rot cannot tolerate these dry conditions and will become dormant and eventually die. The conditions for dry rot is most likely in places where there is damp plaster, damp masonry, damp mortar and enclosed damp walls, cellars that are dark, stagnant and not ventilated. In some cases, masonry will never dry. Northern States seldom experience dry rot. Utilizing heating and air conditioning in modern buildings in the Southern States eliminating moisture problems has rendered it very difficult for dry rot to occur. Well-seasoned timber does best when it is able to breathe eliminating interstitial condensation through ventilation. Dry rot cannot exist in kiln dried lumber or thoroughly seasoned timber when the excess of moisture has been eliminated.
Wet Rot
Wet rot refers to several different kinds of fungi spread by asexual spores but the treatment is the same in all cases. As with dry rot, the asexual spores must be present and wet rot cannot take place if the timber has been thoroughly seasoned and the excess of moisture eliminated. Kiln dried timber will not rot because there is not enough moisture. The moisture content has to be a minimum of at least 23 to 25% for most species to begin to germinate. Wet rot is more likely to occur in unseasoned wood or wood covered with paint or plaster not allowing the moisture to escape. Wet rot can only happen by actual contact and if it is cut out the timber kept dry will not be affected any further.
Wood Destroying Organisms
The main component of wood is cellulose, the natural sugar in fresh wood. Its primary purpose is to energize and give nutrition to the growing tree. Decaying wood is a natural environment for wood destroying organisms that rely upon cellulose and long standing moisture content with oxygen to survive. Take away any of these organisms and they will not be able to survive. Most wood boring insects must lay their eggs in the summer. All wood destroying organisms have to have the right amount of high moisture content but not too much moisture as extreme moisture will also kill the fungi they need to survive on. Freezing temperatures kill most species of fungi and wood boring insects. If any of these organisms are in excess, too minimal or removed they cannot survive.
Nature, Phenomenally Marvelous!
For decomposition, fermentation or rot to occur timber has to have the right combinations of carbonic acid, hydrogen and moisture over a long period of time. Not that we would consider it marvelous from our perspective but considering all the necessary environmental conditions for wood destroying organisms to survive it is a phenomenal, amazing, wonder of nature that they are ever able to progenerate. On the other hand, nature astounds us that when timber is pressure treated or well seasoned rendering its sap inactive or removing it, it will not rot but contains the inherent properties to last indefinitely! Now, that is phenomenally marvelous!
Additional Posts in this series:
A Closer Look at Trees
In Awe of Mother Nature
Timber – Historically Strong & Architecturally Stable
Old Wooden Barrel in an Old Timber Building
