Ironwood Australia talk about water in wood

In the last month we have laid a new range of floors in our Rozelle showroom and have also decided to show off a few new flooring finishes.

The new flooring finishes we have chosen are Synteko Classic and Feast Watson's Alkathane, both of which contrast with our existing 2-pack polyurethane showroom floor. The aim is to provide architects and our walk-in clients with a showroom that clearly shows off the huge differences between the flooring products that are available.

In point of fact, our research was so confusing that we have prepared a very detailed and well researched flooring finish product guide that we will release shortly.

Keith Mackenzie
Managing Director

Feature Article - Characteristics of Timber
Water in Wood

All live trees or freshly cut timbers contain water. The moisture content of freshly sawn timber is in the range of 60% to 100% - which means the water component can be as high as one part water to one part wood substance.

Freshly cut timber will gradually loose the bulk of its moisture until it reaches a level similar to that of the surrounding atmosphere (normally 12-14%). This loss of moisture is referred to as seasoning or acclimatising.

Timbers that are to be pressure treated with preservatives in the sapwood must be seasoned to allow sufficient room for the preservative treatment to replace the water. Poorly seasoned timbers will result in uneven and low levels of preservative treatment. Only the sapwood can be successfully treated with preservative treatment as the vessels, which provide a pathway for the treatment solution, are blocked in the heartwood and therefore stop penetration.

The level of moisture in wood will affect its properties and therefore will influence its suitability for different purposes:

• The weight of green timber can be as much as twice that of seasoned timber.
• As a rule, dry timber is considerably stronger than green timber.
• Timber having a moisture content less than about 20% will not rot. An established ratio of both water and air are necessary for fungal activity to take place. Although fungal spores are common in the air they cannot develop and attack wood unless the moisture content is above 20%. Dry wood therefore will not rot.

The moisture content in timber is particularly relevant with flooring. Every 1% movement translates into a 10mm contraction or expansion of the timber across a width of 4 metres. This movement will recur for the duration of a floor's life. (The longitudinal movement of a floor is lot less significant and usually is not of great concern, except in extremely large areas).

Borers

Damage to timber by borers is generally minor and rarely needs treating. Most borers are beetles with a four stage life cycle. Some of the more common types include:

• Powder Post Beetles (Lyctids), which attack only the sapwood of certain hardwoods. The timbers are usually treated at the milling stage.
• Furniture Beetles (Anobiids) mainly attack the sapwood of softwoods, preferring well seasoned timbers such as Baltic pine and damp humid sub-floor conditions floors. These beetles are a hazard to old buildings and active infestations should be treated. They produce a gritty fine salt when active.
• Pinhole borers infect only green timber and die as the wood dries so no action is required.

Defects in Timber

Timber will lose moisture more quickly from the end grain than across the grain. As timber near the end grain shrinks quicker than adjacent timber that has not lost the same amount of moisture, stresses will be formed that can only be relieved by the formation of small cracks. The size and seriousness of this cracking will depend to a large extent on the wood species.

Large lateral splits in timber sections can affect both the strength and durability of the timber. If cracks develop after the pressure treatment process has been completed, areas of untreated wood will be exposed to fungal spores, insects etc and be potential problems in the later life of the timber.

Growth stresses can also produce serious splits in the ends of timbers. These occur because the outer portion of a tree trunk is often in longitudinal tension while the inner section is in compression.

The outside layers of seasoned timbers that are constantly exposed to outside weather conditions continually absorb and release moisture. As the timber dries the outer layers compress or shrink, thereby re-opening original drying cracks. Repeated wetting and drying over the life of the timber will see these cracks enlarge, providing possible access for fungal infection. This often occurs on horizontal timber surfaces such as the top of crossarms.

In an effort to reduce the susceptibility that timber has to end splitting newly cut beams and posts often have a nail plate affixed and are also painted. These measures are taken to (a) hold the timber heart in place while the timber's tensions realign themselves and (b) slow down the moisture loss. Recent research indicates that end-grain glues are probably the most effective at sealing the end of a timber and holding it together.

Timbers also have a tendency to twist during the drying process because of spiral structure within individual cell walls. There is very little that can be done to prevent the twisting other than laying the timber flat and holding it in position while it dries.

Preventative Conservation

Keeping timber in buildings dry and well ventilated will significantly reduce the risk of:

• Swelling and shrinkage cracking;
• Fungal rot;
• Attack by termites and some borers.

• Large 300mm x 300mm sections are available in recycled. It is now almost impossible to find these in new timbers.
• Recycled timbers are generally more stable and durable as they were probably sourced from old growth forests. Over time the tension in the timber has reduced so they are less likely to split and bend unless a new cut upsets the balance in the original timbers.
• Weathering and features such as bolt holes, surface checking and check outs add character and history to the timbers. This is much sought after and is often a taking point.
• A range of aging colours and finishes are available with antique timbers, including grey or fresh cut, rough sawn, wire-brushed, sand blasted and dressed.
• Ironwood can mill your timbers to size and provide long lengths if necessary. We also have a range of recycled floorboards in our showroom.