Moisture Content
Wood Panels, as is the case with many other building materials, will respond to changes in relative humidity of the surrounding air. Their dimensions are closely related to their moisture content. Under stable conditions all wood products tend towards an equilibrium moisture content and a subsequent stabilisation of dimensions. Particleboard and Medium Density Fibreboard will normally be supplied with a moisture content and a subsequent stabilisation of dimensions. Particleboard and Medium Density Fibreboard will normally be supplied with a moisture content in the range of 9% - 12 % at the time of dispatch from the factory.
Equilibrium moisture content will normally be in the range of 10% - 12% when used in building intended for human occupancy. Boards should be conditioned for 48 hours to reach the humidity level in which they are to be used.
Absorption and Swelling
The most significant effect of moisture absorption by Particleboard and MDF is thickness swelling and if wetting occurs there will be a small amount of residual swelling after the product has dried out. The MR types of both products exhibit a much slower response to wetting than do the standard types. This slow response rate, together with overall lower dimensional changes, are advantageous in these circumstances and residual swelling should not be noticed unless the panel receives a prolonged soaking.
When Wood Panels are exposed to changing relative humidity conditions the following changes should be expected for each 1% change of moisture content.
Linear Dimensions 0.03 - 0.06%
Thickness 0.3 - 0.5%
|
