3.2Conditioning

HPL and substrates should be conditioned jointly before processing in order to obtain a similar moisture content for both materials. Materials which are processed when moist tend to shrink over time, which in turn can lead to cracking and warping. Materials which are too dry are more difficult to process and may expand later on, possibly leading to warping. The climatic conditions during subsequent use are always to be taken into account when planning and designing composite elements. Optimal conditioning can only be achieved in a normal room climate (i.e., at approximately 18–25 °C and 50–65% relative humidity).
Sufficient air circulation around each sheet for at least ten days (see figure below) is recommended. In addition, HPL and substrates have to be stacked in the order in which they will be bonded later on for at least three days. The relative humidity should be similar to that of the future application.
 

1 Stack with substrate boards | 2 Stack with HPL 3 Preconfigured stack with a Tsubstrate boards |b HPL

These recommendations apply to the processing and subsequent use in moderate climate zones. For extreme climate zones we recommend consulting the manufacturer.

If the composite element which is to be manufactured will be exposed to continuous low relative humidity during future use, it is recommended to expose the HPL and the substrate to a corresponding humidity during conditioning to anticipate subsequently occurring shrinkage stress. Bonding has to be carried out immediately after conditioning. We also recommend consulting the manufacturer about this.

Suitable conditioning is to be observed during transport as well.