Wood warping nightmares…………
Improperly dried or stored wood may suffer from cracks
and deformations due to shrinkage, while it may twist, bow, crook or warp
caused by a combination of shrinkage and swelling. This is caused by the
moisture content (MC) of the wood. The higher this content the greater the
chance that one or more of these negative effects will occur.
The moisture content is measured as the ratio of the
weight of the free water in a given piece of wood to the weight of the wood
when it is completely dry (oven dried, or kiln dried) and is usually
expressed as a percentage.
The "green" wood of a freshly felled tree may have an MC
anywhere in the range 30% to over 200%, depending on the species (hardwood
(*) is far less receptive for a high MC than soft wood). Almost all of his
water must be removed from the wood before it is fit to be used for its
particular intended purpose (wood for furniture shall be dryer than wood for
railway ties).
Wood for structural purposes is considered dry when a
moisture content of 15% to 20% is achieved. This implies that all of the
free water has been removed and only bound water remains, some 10% to 15%
below the fiber saturation point (saturation point is defined as the
boundary between free water and bound water. Cracks and warping will occur
in the saturation zone, not in the bound water zone).
Furthermore, wood is a cellulose material which behaves
somewhat like a sponge, so that even wood which has been kiln dried down to
say 7% may in fact later reabsorb water from the atmosphere. Actually all
wood is constantly gaining or losing water to or from the environment, in
other words, the moisture content of wood changes as the relative humidity
changes. Coats of varnish or paint can slow the process but cannot stop it.
As the moisture content of improperly dried wood (or
green wood) changes, so does the wood expand or contract, potentially
producing all manner of disastrous defects (wood warping and wood cracking
nightmares).
Most of the wood for our bungalows and cottages is kiln
dried to an MC of 12%. When arriving at destination this MC may have
increased to a maximum of 20% depending on the humidity of the environment.
This MC percentage of 20% is still 10% lower than saturation point, thus in
the bound water zone and in conclusion safe against cracking and warping.
The wood that we use is kiln dried to 12% MC.
(*) Teak, Merbau, Iron wood, Bangkirai and Mahogany are
the hardwoods that we use. Coconut wood is a soft wood.