Protective coating
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PROTECTIVE COATING

In order to provide the finest, furniture grade home, Bali Wood Houses 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 vast majority of other wood species can match Bangkiraiís 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)

Some wood species that are kiln dried may be immediately finished without being seasoned.  However, none of these species is termite resistant like Bangkirai.

OPEN AIR DRYING

Based on research performed by Akzo Nobelís 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.

Properly Seasoned and Finished

 

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, polyurethanes, Cetol, 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.

The commercial lumber industry could not possibly store and process enough wood to properly season it.  Kiln drying is a more rapid method by which they can deliver a useful (though far from ideal) product. 

When Bangkirai is not properly seasoned, the near term consequences on the finish are shown in the figure below which is a photograph of a one-year old gazebo post (not built by us):

Consequences of Improper Seasoning

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.

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Last modified: November 03, 2013
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