A wood structure will not last long if it is not properly protected against environmental conditions and pests. While a number of hardwoods have its own natural protection in the form of tannins bound in cells, density of the wood, hardness and other natural protective measures, giving all hardwoods a significantly longer life time compared to soft wood, it needs to be treated and maintained to extend the life time and protect it from exterior factors not dealt with. In addition the moisture content , - called MC -, before the wood is worked, cut and planed is of crucial importance for its life time.
These protective measures are: coating, kiln drying and anti termite measures.
WOOD AGING & KILN DRYING
In order to provide the finest, furniture grade home, Prefabworld Bali International © has researched countless finishing processes used not only in hardwood and log home construction, but also in the fabrication of furniture, wood art and fine musical instruments. A key element common to the finest wood products is seasoning or aging of the wood after it is milled into dimensional lumber.
For many years we falsely believed that the gold standard for wood processing was Kiln Drying. We are not saying that kiln drying is always inappropriate, since we fully agree that some furniture applications require lumber with very low moisture contents that cannot be achieved with natural air drying, aging and seasoning.
Kiln drying is quite appropriate for many wood species. For example in the United States, oak is the dominant hardwood that is kiln dried and successfully used for furniture and flooring for centuries.
However, neither oak nor a vast majority of other wood species can match Bangkirai’s properties such as:
1) Unequaled Termite resistance
2) Extreme hardness
3) Very High density
4) Tendency to leach extractives over months (or years if kiln dried)
OPEN AIR DRYING
Based on research performed by Akzo Nobel’s Sikkens © coating division, we have learned that kiln drying of some species such as Bangkirai prolongs the extraction of tannins and other extractives that if left in the wood will ultimately result in failure of any finishing method.
All hardwoods should therefore be left uncoated for as long as possible, and be air dried in the open (for instance during the assembly process) until all extractives have leached from the timber fibers and the timber is thoroughly dry (*). For oily resinous timbers such as Merbau a minimum of 3 months is recommended. For very dense, slow drying timbers such as Bangkirai a minimum of 6 months is necessary. During this seasoning period we must regularly clean all wood surfaces to remove the extractive materials that leach from the wood as it seasons such as tannins, as well as ensure that the moisture content stabilizes and adjusts to the surrounding climatic conditions. The method for regular cleaning is critical and if not done properly or carefully can damage the wood and affect its termite resistance. It is therefore not an advantage at all to assemble a wooden prefab house under cover since weathering will be prevented (no sun, no rain) and thus the proper drying of the wood is at stake (*).
In conclusion: Prefabrication carried out in the open has major advantages with respect to the holding and lifetime of the applied coating.
(*) Source: Akzo Nobel Sikkens, Australia
The requirement for proper seasoning is independent of whether the finishing method is French Polishing, or Cetol.
|Since the many islands in the Caribbean and the Pacific and Bali share similar climates, the resulting moisture content internal to the wood will be very close to the equilibrium moisture content that would be achieved and required for homes destined for those areas.
Please note that kiln drying does not remove extractives from the timber fibers and generally dries the wood beyond equilibrium conditions. Exposing kiln dried hardwood to tropical climates causes the extractives to begin leaching (but at a much slower pace) and the wood slowly increases its moisture content.
This leaching will cause flaking and failure of any coating system applied to the wood (French polishing, Acrylic, oil based paints, oils, etc.) and the absorption of water will cause the lumber to distort. The reason that kiln drying slows the leaching process is because the internal moisture of the lumber is a major mechanism in transporting the extractives to the surface of the wood where they can be removed.
The weathering that occurs during the seasoning process has several aesthetic affects:
1) The color and grain contrast deepens. This is quite desirable.
2) Some very small surface cracks will result. These are removed during step 6 of our seasoning process discussed below.
3) Some graying of the exterior surfaces will result. This is fully removed during sanding (step 6 of our seasoning process discussed below) but does not affect.
Seasoning of wood for use in our homes is a multi-step process.
1) The timber is harvested using only sustainable forest practices and is sent to a mill where it is cut into the various required sizes. The time from milling to delivery ranges from 1 to 2 months.
2) Our factory receives the wood and immediately performs our proprietary process cleaning to remove the extractives that have already migrated to the surface.
3) Seasoning continues at our factory during the hot season when rain is rare. Stacked lumber is rotated to maximize exposure to the heat of the sun and accelerate the seasoning process.
4) The lumber is used to construct your home before it is fully seasoned. For this reason, we fabricate many homes simultaneously and do so in the open where the lumber is exposed to the sun and elements. This exposure more thoroughly exposes all surfaces. The fabrication time is intentionally extended as necessary to ensure that the extractives are thoroughly removed prior to any finishing.
5) Any boards exhibiting cupping or distortion are straightened or replaced. Straightening requires us to dismantle the boards, turn them, recondition the lumber, fix them tightly back to the support beams (or clamp them) and allow the boards to return to equilibrium stress conditions. In the vast majority of the cases the boards return to their original straight shape. If further cupping occurs, we repeat the process or replace the board.
6) All surfaces to be finished are rough and finish sanded, after assembly to remove the final traces of extractives and prepare the wood to receive the final finishing process.
The above process is both time consuming and expensive. However, without taking these steps we cannot provide the quality product our reputation demands and our customers deserve.
OUR COATING SYSTEM
The primary purpose of paint is to protect wood from deterioration. To do so, paint manufacturers have developed paint systems which are made to work together to protect the wood substrate. These systems include primers and appropriate, compatible top coats which can vary depending on the substrate and can vary between manufacturers. As a result appropriate primers and compatible top coats, both from the same manufacturer should be used.
We have chosen for the use of Acrylic rather than an oil based coating for a number of good reasons.
* It dries quickly,
* Despite the fact that acrylic paints can be diluted in water it is highly resistant to water once it has dried
* It emits very low VOC's (*), thus ECO friendly
* The paint is highly elastic, able to expand and contract without splitting
* The paint has excellent color retention and possesses better resistance to sunlight and the elements than oil-based paint.
* Provide better resistance to mildew because thereis no oil in the paint. The oil of oil/alkyd paints acts as food for mildew
* Excellent protection (washability)
* Good water resistance
* Excellent adhesion to top coats
* Decreased odor, toxicity and flammability (due to lack of organic solvents and thinners)
* Excellent color and gloss retention
* Resist cracking and blistering better
* Resistance to alkali cleaners
(*) Volatile organic compounds which have a high vapor pressure at normal room temperature. I it is toxic and long-term exposure to VOCs in the indoor environment can contribute to sick building syndrome. Health effects include eye, nose, and throat irritation, headaches, loss of coordination, nausea, damage to liver, kidney, and central nervous system. Dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics. VOC's are found in oil based coatings (enamels, alkyd) and some acrylic paints. The type of Acrylic that we use emits very low VOC's, hence safe for the painters at work