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Diseases and Defects. Trees are living organisms so they are prone to diseases and defects. Diseases and defects affect the strength and quality of the wood however, it can make the timber more valuable because it looks well. Timber we get from trees can be subject to any of the following:
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Diseases and Defects • Trees are living organisms so they are prone to diseases and defects. • Diseases and defects affect the strength and quality of the wood however, it can make the timber more valuable because it looks well. • Timber we get from trees can be subject to any of the following: • Natural Defects • Artificial Defects • Fungal Attack • Insect Attack
Natural defects • Natural defects are often pleasing to the eye while others are unwanted defects. • Heart Rot- caused by a fungus that rots the pith or the heartwood • Spike Rot- reduces the strength of the wood • Spiral Grain- tree may twist when growing
Knots • Knots form where branches of a tree are cut off or stop growing • Loose knots are called Dead Knots – branch has stopped growing before tree is felled • Other knots are called Live Knots • All knots reduce the strength of the timber.
Resin Pockets • Most common in conifers • Forms in internal cracks/cavities in the wood • Cracks caused by high wind or extremes in temperature • Reduce the strength of the timber
Natural defects • Shakes- these are splits in the end grain. They are either Radial, Tangential or Cross(thunder) shakes • Radial- along ray lines include heart or star shake • Tangential- in annual rings at old age, seasoning or strong winds • Cross-split across the grain when tree is subject to shock in felling
Artificial Defects • Artificial defects occur as a result of stresses caused by poor stacking or seasoning. • They include: • Cupping • Bowing • Twisting/Warping • End splitting • Case hardening • Honeycomb checks
Artificial Defects • Cupping-this form of shrinkage forms a curve if you look at the plank from either end. Caused by incorrect stacking during seasoning. • Bowing-where the timber is taking the form of a bend along the length of the piece. Like cupping,it is caused by incorrect stacking during seasoning, often the incorrect positioning of the stickers.
Artificial Defects • Twisting or warping-the two ends of the piece have twisted in opposite directions while the sides of the piece have remained straight. • End splitting-this is caused by the end of the piece drying out too quickly. Most common in natural seasoning where there has been excessive exposure to the heat or sun. Can be prevented by covering or treating the ends during seasoning.
Artificial Defects • Case Hardening-this occurs when the piece is seasoned too quickly and moisture is still trapped within the wood. The surface and the centre have different drying rates creating compression at the centre and tension at the surface. • Honeycomb checks-the inside of the wood splits and like case hardening the timber is seasoned too quickly for the centre to be dried out. When it does there is shrinkage causing splits within the piece.
Fungal Attack • Fungi attack causes damage by feeding on the cells of the wood. The wood becomes soft and eventually decays. • A fungus is made up of cells called hyphae. A large number of hyphae together will form a mycelium. These hyphae penetrate the wood to feed and get moisture. They will then produce food bodies called sporophores. The cycle will now repeat itself when the spores produced are blown on to new wood. • The following conditions are required: • Moisture • Food supply • Oxygen • Warmth
Fungal Attack • Wet Rot (white rot)-Usually occurs outdoors where it will rot fence posts, window frames, logs, doors, etc. The affected wood will become very moist and slimy and will produce a white residue. • Dry rot (brown rot)-This type is usually found indoors, eg under wooden floors. This fungi attacks wood and eats the cellulose found in the wood. Wood will appear dry and contain rectangular cracks in it. Treatment of this type of rot must be immediate and severe as the rot can cause extensive damage.
Fungal Attack • Treatment process • All infected wood needs to be removed as well as uninfected wood 500mm around the area. • All surrounding brickwork and materials must be scorched or treated to kill remaining fungicide • The cause of the dry rot must be remedied before new preserved timber is put in place.
Insect Attack • Some insects will attack and feed on timber much like fungal attack. • The adult lays the egg in an old insect hole • The egg hatches and the larva/grub will feed on the starch in the wood – this creates the tunnels • The larva makes a cocoon-like shell around itself before it settles for a period of time to change into an adult bettle. • The adult then emerges and breaks out to the surface to begin the cycle again.
Insect Attack • Furniture Beetle (woodworm)- this common beetle, more often known as ‘woodworm’ is probably the most common in Ireland. Woodworm will attack both softwoods and hardwoods, mostly just the sapwood of these timbers.
Insect Attack • Treating timber with woodworm • Apply coats of insecticide following the instructions on the container. • Ensure that all surfaces and cracks are coated with the chemical • Use an applicator to insert insecticide to the exit holes of the woodworm.
Insect Attack • Deathwatch Beetle- this beetle is not so common in Ireland, but will be found in Southern England. It will attack damp timber, usually where it is embedded into walls. If timber is painted it will greatly reduce attack • Powder Post Beetle-It is reddish brown in colour and generally attacks the sapwood of new hardwoods particularly during or after seasoning.
