What are Acceptable Moisture Levels in Wood for Woodworking?
Wood is hygroscopic, so the acceptable moisture content in wood for woodworking depends on two factors:
The wood’s final usage.
The average RH of the environment where the wood will be used.
So there is no general answer to this question. But based on common guidelines or recommendations, the acceptable moisture levels for wood for some woodworking projects are as follows:
Wooden objects used indoors: 6-8%
Wooden flooring: 6-9%
Construction (Outdoor projects): 9-14%
Why is Wood Moisture Content so Important?
Since almost all physical, mechanical, and technological properties of wood are strongly dependent on its moisture content, its study is very important. Also, understanding the adsorption behavior and loss of wood moisture can be of great use in wood drying. In addition, this issue guides us in determining the amount of wood material in forest stands.
1- Correlation with Specific Gravity in Wood
Specific gravity indicates the amount of actual wood substance present in a unit volume of wood. Changing the moisture content directly changes the specific gravity of the wood. In this regard, the specific gravity of wood is always mentioned with its moisture content. The specific gravity of 12% moisture is called the normal specific gravity of wood. By knowing the percentage of moisture and specific gravity of wood in a forest mass, we can estimate the dry weight in that forest mass. The importance of this is well understood in paper mills that consider the dry weight of wood.
2- Correlation with Changing the Dimensions of Wood
These two properties are directly related to each other and always increasing the dimensions of wood is the result of increasing its moisture and vice versa. But at more than FSP, which varies from 25% to 50% for different species and habitats, the dimensions of the wood remain the same.
3- Correlation with Electrical and Thermal Properties of Wood
The electrical conductivity of wood increases with increasing moisture, but its electrical resistance decreases. Increasing the thermal conductivity of wood depends directly on the amount of moisture.
4- Correlation with mechanical quality
Changes in wood moisture directly change the resistance of wood to different forces. This is so important in wood mechanics that a certain coefficient is assigned to it. In addition, the results of all mechanical tests of wood, according to international standards must be provided at the moisture of 12%.
As the moisture increases, the strength of the wood decreases. Therefore, in wood consumption, its moisture is usually reduced to less than 20% by wood drying methods.
