HOW DOES WOOD ROT?

I order to live all life tends to need other life forms for its survival, sometimes that life form is totally consumed or killed, as in animals eating other animals, In plants or vegetable life forms part of the plant is consumed but carries on living, everything is part of the food chain.The ultimate source of life energy is sunlight. It is captured by plants who store most of it in their physical and chemical structure and use up the remainder. They are eaten by animals, and sometimes by fungi. Some of those animals are eaten by other animals. Some of the plants and animals, who were lucky to not be eaten entirely by others, eventually die. Animal’s plants and fungi also feed on the dead thereby continuing the wheel of life.

Sometimes I see a tree as solidified sunshine for when it is burnt the only matter left is ash, or in other words, minerals. The tree has changed back into heat, that life giving radiation from the sun.
As a defence, some life survives best when it tastes bad to whoever is trying to eat it at that moment. This is why some kinds of wood are more resistant to fungal attack and rot than others; those trees taste the worst and they were the ones that survived. Different trees taste bad to different predators or parasites. Life is diverse.

Fungi are primitive and one of the oldest life forms on this planet. Fungi feed on just about anything whether dead or alive. Fungi move by growing more fungal cells that spread further by growth. When a cell of fungus is in contact with something, the cell secretes digestive enzymes onto what it touches. The enzymes usually can break down the surface and dissolve it, and the cell absorbs the digested material as food.

There are also bacteria, a different kind of microscopic single-cell life form. They are more like an animal than a plant, and more like a fish than an air-breathing animal. Bacteria tend to prefer the wood more damp than do fungi, but there is a humidity range where both can live.

Wood is said to breathe, because the natural humidity of wood, perhaps five to fifteen percent by weight (once it has sat around in your garage for six months) can go up and down a bit as the humidity of air varies. The air humidity ranges from maybe ten percent in a dry summer to perhaps ninety-five percent in a humid summer.

Humidity (of air) means how much water vapour is dissolved in the air. Ten percent humidity means the air is holding ten percent of its maximum capacity. Ninety percent atmospheric humidity means that the air has, dissolved in it, ninety percent of its capacity. At one hundred percent humidity it is raining.

Wood can actually be placed in a box and exposed to the hot steam from boiling water. After a few hours the wood becomes flexible and can be bent into a new shape. If the wood is held in that shape as it cools down and dries back to its natural humidity at room temperature, it holds its new shape. The curved ribs for many small boats are made by this "steam-bending" process.

Wood holds a little water very strongly and more water with less strength and even more water rather casually. When there is less humidity in the air, wood loses some of its water to the air by evaporation. When atmospheric humidity is high, damp wood may lose some of its water but really dry wood will actually capture some water from the air. You may have noticed that small branches of plants are very flexible. That is because the wood is full of water. As wood dries out it becomes stiffer. Old wood found in the desert is not only hard but brittle. You may have noticed how brittle a dead branch of wood in the summer.

Wood, microscopically, consists of bundles of large hollow tubes with doors across the tubes every so often. These tubes are the walls of living cells, long since dead with only the skeleton remaining. The hollow tubes, the cell walls, are the skeletons of those cells. As the fungi eat away those cell walls, they open up the spaces between those tubes, and as the fungi dissolve the doors between one wood cell and the next, the wood porosity is opened up more and more. This allows more rainwater to be more rapidly absorbed in the wood, thus providing more humid wood which is more favourable to rapid fungal growth, thus accelerating the decay of the wood. As the wood becomes more porous it holds enough water to favour growth of not only fungi but bacteria, and between them they eat first the porous summer growth rings and then the harder winter growth rings, and finally there is nothing left.

By choosing the right timber for the environment the need for preserving wood can be lessoned. Oak Sweet chestnut and Larch and the Cedars are very durable woods that can be used untreated outside. Teak is one of the best but I cannot buy it from sustainable sources. Only buy teak furniture if the wood is certified as being from well managed forest or plantations. Britain has very good regulation when it comes to copping trees down and if you want to fell more than a certain volume you must get a felling license from the forestry commission. Other countries have no or very little regulation and millions of hectares of wild ancient forest are being totally destroyed for ever. This is usually driven by big business who grow palm oil, for example.

If you can bring inside any wood products during the winter the products life can be dramatically extended.

If you do need to treat your wood there are many products on the market, avoid stuff like yacht varnish for garden furniture as if it gets damaged and water seeps in which can then lift more varnish as well as exposed areas going dark in colour. Companies like Ronseal and Sikkins do exterior finishes that are said to last up to 5 years. It can be the case of the more you pay the better the product. I am in the process of testing various products and will report back in a few years time.

Do read the information on the tins well, as some coatings are not suitable for furniture and are made for fences and sheds, they could stain or damage your cloths.

I have tried oiling exterior wood with Danish, Linseed or Teak oil, if you want to go down this route you will have to be committed to re oiling regularly, up to 3 times a year. Oils will wear off and also get washed away by the rain.
If you oil exposed untreated wood that has gone grey with age the wood will go even darker.

One exterior preservative is borax and is often considered as ecological, if you use borax alone it will get washed out by the rain very quickly.

I have also made furniture from pressure treated wood, all agricultural and landscaping woods are treated this way. The pressure treated woods are great as the preservative is forced right into the cells of the wood. Do not burn pressure treated woods as in the near past they used chemicals such as arsnic chromates and copper, not good stuff to breath in even in small quanities.

Sean Hellman shows at woodfairs in the South of England, click here to find a list of woodfairs

Copyright Sean Hellman 2007