"In particularly indoors, dry air slowly evaporates the water that the living tree carried; the wood shrinks, it cracks and warps – its natural behaviour."
Wood is like a sponge, it soaks up moisture. No matter how dry your sponge gets, you can always get it to soak up water. Even kiln dried wood will acclimate water from the air. After all, this is what it is designed to do naturally. When the tree is alive and standing, it brings water from the ground through the roots and up to the limbs and leaves. The cells in wood are designed to absorb and hold moisture, just like the holes in a sponge.
Wood expands when it draws moisture, and contracts when it dries out. Boards expand and shrink more on their width, than on their length. The wider the board, the more it shrinks.
Our grandfathers discovered this shrinkage and expansion in wood many years ago, that is why when you see old hardwood flooring it is usually 1 1/2 to 2 inches wide. The narrow flooring will still expand and contract, but it is more spread out so you will have smaller gaps between boards. However, nowadays one would prefer wider boards, increasing the danger of cracking and deformation. The solution: both air drying and kiln drying may limit the chance of these deformatiosn ocurring significantly
In a home you have a controlled environment. In the winter when you heat your home the air dries, the humidity level drops and therefore your hardwood floor dries out and it shrinks. In the spring and summer the air in your home is more like the air outside and the hardwood soaks up that moisture and expands. It is inevitable, wood will absorb the moisture in the air. No matter what you do, wood will always acclimate to the environment it is in. This is why hardwood much better behaves in a tropical environment than in a cold environment. Higher tempeatrues and almost constant high humidity deos the trick.
KILN DRIED VS. AIR DRIED
Some believe that the wood should be kiln dried. While others think that the air dried wood is far more stable than anything out of a kiln. It really depends on how quickly a client wants his prefab home built. Air drying may take a long time, while kiln drying takes around 6-8 weeks. The best is a cobination of the two.
Kiln drying is only effective, if proper drying techniques are followed. The faster the wood is dried the more likely it will shrink to fast, causing it to check, warp, or crack. Contrary to popular opinion, kiln dried wood has no advantage over air dried wood. At least as far as moisture content and stability is concerned. Kiln dried wood will gain moisture at the same rate as air dried wood.
The more time a client allows us to dry the wood, the better the quality and the lower the chance that the wood wll crack or warp.