When we first started selling moisture meters 40 years ago, many woodworkers asked: Why do I need a moisture meter? The answer: Because all the hard work, money, and time invested, cannot prevent shrinkage of wood when loosing moisture. The example of White Oak shows how much wood shrinkage can happen due to moisture loss.
To demonstrate shrinkage, we obtained a board of semi-dried White Oak with a moisture content of 18%. We then cut two pieces of the same size from the same board — 4″ wide, 1″ long and about 1/4″ thick. The moisture content of one piece remained unchanged at 18%, while the other piece dried down to 8%.
The flat-sawn board of white oak, with the grain parallel to its edge, shrank substantially when drying from 18% to 8%.
The difference in width was surprising. The significant shrinkage in the dry piece was attributed to both the selected species (White Oak, known for its high shrinkage factor) and the orientation of the grain. Notice how the grain runs almost parallel to the width of the board. Tangential shrinkage in a flat sawn board is almost twice as high as radial shrinkage. S Shrinking calculator.
Every home has moisture-sensitive areas such as entrance ways, kitchens, and spaces near showers. In these areas, it is best to use wood with a small shrinkage factor and grain as close to quarter-sawn as possible to reduce shrinkage.
Why Is Shrinkage Unpredictable?
What makes wood so special is that every board has a unique structure, created by the growth rings. The different orientations of these rings cause wood to shrink and warp unpredictably, often causing defects in woodwork, furniture and wood floors.
The growth rings in trees form a series of more or less concentric cylinders. These cylinders consist of irregular tubes that, in a life tree, transport nutrients and support the tree. When a tree is cut down and sawn into lumber, the growth rings are still part of each board. When moisture in dry wood changes, the tubes swell or shrink. The most significant shrinkage occurs along the growth rings, and the least amount happens between them. Because each board has a different structure of growth rings, the potential for shrinkage and warping varies from board to board. The example of White Oak shows tangential shrinkage due to moisture loss from 18 to 8%.
The best tools and the highest level of craftsmanship cannot guarantee a quality product if the wood is not right. Grade, species, and moisture content determine the usefulness of wood.
Moisture Loss and Relative Humidity are Key to Stable Wood Products
Two tools can help you to predict moisture problems:
– wood moisture meter
– thermo-hygrometer
Combined with the EMC chart, you will see what the right relative humidity is to keep your wood stable.
You need both a wood moisture meter and hygrometer to understand how wood will react to its environment.