Moisture meters were originally designed to measure wood moisture content, but people often attempted to use them to test other materials, so the devices were developed to do this more effectively.
The devices are still primarily used on wood; however, some can be used on other materials, such as plasterboard, concrete, cardboard and paper.
These moisture meters are most reliable when used on wood, but they provide an accurate enough idea of moisture levels in other materials to be suitable for most tasks.
Wood moisture content
When a tree is felled, its water levels will be high – eighty percent or more. Before it becomes wood suitable for use, the tree must go through a drying out process.
Wood can either be air or kiln dried, and while the exact levels are dependent on the type of wood, the moisture levels will most likely need to be under twenty percent for timber to be suitable for use.
As wood dries, it changes shape and size This is why it is important to ensure moisture is at a suitably low level before beginning to work it. You do not want the table you put all your time and hard work into warping with a change in the season.
If you imagine a cross-section of tree trunk, there are three ways in which shrinkage can occur:
Across the radius (radial)
Down the length (longitudinal)
Around the circumference (tangential).
Moisture content in other materials
For other tasks, the exact levels are not as important as knowing if the levels are present or high, making moisture meters ideal for this too. The reading for other materials will generally not be in the form of a percentage, but instead use a reference scale.For more information on reference scales, see: What is a reference scale?
Tasks which may require the checking of moisture levels include:
Building inspections, or in the diagnosis of damp problems in plasterboard and brickwork.
Checking of subfloors and walls for moisture that is not visible at surface level.
When floor fitters need to ensure the subfloor and the wooden floor are at similar moisture levels, and to allow the flooring to acclimatise properly.
