All building materials require care in handling at all stages to prevent unnecessary damage and to ensure they provide optimum performance in service. Timber is no exception.
Manufactured wood products and seasoned or treated products in particular need special consideration.
These requirements are appropriate for both appearance graded products and structural timber.
• Keep timber flat - Timber may twist, bow or cup if transported in a bent condition. It should be bundled and stacked at all stages so that it is flat. This is necessary even for a short trip across town on the back of a truck.
• Protect corners of packs - Part of the care of the timber is the use of corner protection under straps used to bind packs.
• Protect seasoned timber from moisture – packs of seasoned timber must be wrapped in plastic for delivery and storage on site
• Arrange delivery to fit in with construction sequence – In ordering timber and arranging delivery on site, multiple handling of timber can be avoided by having the first used pieces on top of the stack. Often the stacking sequence that seems to make sense to the truck driver is opposite to the order in which a builder will want to use the material. For example, the driver will often be inclined to put the largest cross section material on the bottom of the transported bundles, yet these members are often low in the structure (eg bearers) so need to be drawn from the site stock first. If possible, it is best to have the timber members that will be used first in the process delivered near the top of any bundles. However, if that is not possible for delivery, then when stacking the timber in the storage area, it should be done so that the first used timber is at the top.
• Unload timber – don’t dump! - Firewood is often delivered by raising the truck tray and letting all of the wood roll off onto the ground. Some contractors may want to unload building timber the same way! This is very poor practice for a number of reasons:
• The timber digs itself into the ground, making an excellent opportunity for termites to invade it.
• The timber is given a shock loading on impact with the ground. This can cause fracture of some products. In some cases, the fracture may not be seen by trades people on installation, and damaged items may be used in critical locations.
• The resulting pile of timber will mean that many pieces are bent or twisted and will be much harder for carpenters to install.
• Use soft slings and protection for timber on corners of packs - Where the timber is lifted off a truck using a crane or HiAb, soft slings or corner protection under wire slings should be used. If a forklift is used to unload, then care should be taken not to damage the packs with the forks. This is common sense for any valuable building product.
• Use load spreaders for slender assemblies - Some manufactured wood products and assemblies such as I-beams, slender trusses and long LVL beams may be damaged in lifting. Many of these items have high strength and stiffness in one direction (major axis) and are weaker in the other direction (minor axis). f they are lifted the wrong way, and without load spreaders, then they can break under their own weight. Slender items should be lifted in bundles securely strapped and in some cases with load spreaders to give well distributed lifting points.
• Move it quickly to the on-site storage location - Rather than leaving the timber at the roadside where it is exposed to the weather, and not particularly convenient for easy access to the building site, it should be moved to its storage area as soon as possible.
Storage on site
Once the timber has arrived on site, there is still potential for it to deteriorate before service. In many parts of Australia, termites are particularly voracious and may invade timber stacked in contact with the ground for only a few days.
Timber left stacked on site may also get wet if it rains. This does not present any problem at all for unseasoned timber, but if it is seasoned, then swelling may take place.
The following measures are not expensive or complicated, but all of them have the potential to make a difference to the way the timber will perform in service:
• Stack timber flat – stacking the timber flat reduces the chance of the timber warping, twisting, bending or cupping prior to installation. (Once restrained by the rest of the structure, deformation in service is less likely.)
• Stack timber off the ground - Keep the timber away from ground contact. This prevents attack by termites or ground-dwelling fungi, and it also stops the wood from absorbing moisture directly from the ground. Where timber is stacked on gluts or pieces of wood, the gluts should be of higher durability timber to prevent fungi and termites from using the gluts as a route to the timber.
• Stack the timber in order of use - helps to minimise double handling and to find the pieces with minimum trouble later.
• Cover all Seasoned Timber -
Water on seasoned timber:
• Makes it more prone to movement or splitting later on as it dries back out again
• Makes the timber more desirable for fungal or insect attack.
• Makes it harder to paint, and makes protective coatings less effective.
• Stains the timber.
Sunlight on timber:
• Can bleach the surface and lessen its appearance later on.
• Can crack the surface of the timber.
• Cover all appearance products eg joinery, flooring, stairs, cabinetry, etc. Appearance graded products require covered storage conditions for all of the reasons outlined above. Often it is better to delay delivery of these products until after the roof is on. In this way, the building itself affords protection to the stored material.
• Store appearance products inside building for as long as possible - With many appearance products (such as flooring and lining materials) it is recommended that the material be stored inside the building for as long as possible (some weeks) prior to installation. This allows the material to reach equilibrium moisture content. The timber will change its moisture content slowly to arrive at a moisture content, which is stable with the air inside the building. It is desirable for this to have occurred prior to installation so that the timber doesn’t shrink or swell after it is in service. Shrinkage can crack the product or open unsightly cracks, and swelling may cause buckling.
Protection During Construction
In many cases it is not possible to cover timber during construction, but where it is possible, it should be done.
- Minimise the exposure of seasoned timber to weather
- Cover partially completed work whenever possible
• Seal end-grain as soon as possible - End grain of timber presents the ends of the hollow cells to the atmosphere and this can give a conduit for moisture to be transmitted deep into the timber. It is really important to seal the end grain of the timber: Often, the end grain is hidden in the structure, as part of the detailing. In this case, once the timber is in the structure, it is impossible to paint the end grain, though moisture may still find its way into the end grain. It is better to seal the end grain of pieces before assembly. In some cases an end cap may prove the better solution. Paint is often difficult to work into the end grain, as the hollow cell structure tends to suck in the paint in the same way that it sucks in water, but it is worth the effort.
• Apply protective seals or paint finishes as soon as possible – This will preserve the intended appearance of the timber, and offer improved life of the elements.