We Pressure Treat Timber For Two Main Reasons
– Protection against attack by wood boring beetles or termites
– Protection against fungal decay. The benchmark figure for this is where the moisture content of timber is greater than 20% and remains that way. Under these conditions timber will decay naturally.
Situations Where Timber Should Be Pressure Treated
Logically therefore, timber is required to be pressure treated where it is being used and in carrying out its function, it is subject to attack by insects/termites or it will become wet.
How Should The Timber Be Pressure Treated
When deciding if timber should be treated for a particular end use we must carefully consider what conditions the piece of timber will be subject to during its life. Timber is treated into what are called Hazard Classes and for the end uses we are dealing with the two categories are Hazard Classes 3 and 4. The table below details what end use falls into each Hazard Class.
Hazard Class 3 External Joinery, Fence Rails, Decking, Featheredge, Barge and Fascia Boards, External Cladding, External Joinery
Hazard Class 4 Sole Plates (below DPC), Fence Posts, Stakes, Sleepers, Swimming Pool Surrounds
What Timber Can Be Pressure Treated
Different species of timber are selected depending on end use and different species of timber require pressure treating in different ways. When we pressure treat timber, it is not just a surface coating, the treatment actually goes into the timber. Different species of timber have different cell structures which make some more permeable to preservative treatment than others. It follows that the higher the Hazard Class the more treatment is required to penetrate the timber.
How is Timber Made Up
A piece of timber is made up of two sorts of wood, Sapwood and Heartwood.
– Sapwood is the living part of the tree and has cells which transport the water up and down the trunk of the tree. This is found on the outer most part of the trunk beneath the bark. As it is living, the Sapwood contains food stuffs which are attractive to insects and fungal decay
– Heartwood is the dead part of the tree and the cells have closed up. This is found in the centre of the trunk. This part of the timber does not contain food stuffs and in not attractive to insects or fungal decay.
When we treat timber therefore we are treating the Sapwood otherwise it will deteriorate, also it has open cells which can accept the treatment.
When we treat timber we do not treat the Heartwood as it is naturally durable and the cells a dead and closed so will not accept treatment.
When selecting a species for a particular end use, we must therefore consider the following:
– How easy it is to treat the Sapwood
– How durable is the Heartwood
Cladding Timber Selection
All the NORclad range requiring pressure treatment is machined from a high quality European Redwood Joinery Timber with a low moisture content. The timber is treated to a Hazard Class 3 and this species is selected due to good treatability of the Sapwood and the natural durability of the Heartwood.
30 Year Warranty
By selecting the correct Species for end use and then Pressure Treating this Species in accordance with the requirements of a Hazard Class 3 process, all pressure treated cladding in the NORclad range can be offered with a 30 year Warranty against rot and fungal decay. Please see the Warranty Statement.
Micronised System of Pressure Treating Timber
The Norclad range is pressure treated using a revolutionary new wood preserving process. Wood pressure treated with MicroPro technology offers many benefits including a modern fresh appearance, improved colour fastness and Green Guard Certification. Please see separate handouts.