Handling and Storage

All types of composite panels will perform better if properly handled and stored. Since a smooth panel surface is essential for both particleboard and MDF, units should be protected against exposure to water and high humidity.

• Always wear proper eye, hearing, and respiratory protection when fabricating particleboard and MDF.
• Effective storage and handling should begin with a critical observation of inbound shipments. Photograph any problems before unloading and contact the panel manufacturer if necessary, to resolve any issues.
• Unload units under cover where possible. Avoid unloading during inclement weather. Tight straps, which may indent the upper corners of a bundle, are an indication of built-up stresses induced by exposure to high humidity.
• Most panels tend to absorb moisture into their edges more rapidly than through the panel surfaces. This unequal rate of moisture absorption can cause unequal stresses to build in the panels that will be relieved when the panels are cut. Strips from the outer edges may bend, creating what is commonly called a "banana" cut. Allowing the cut part to come to equilibrium will normally straighten these strips.
• Do not store materials outside or in locations where they may be exposed to water or high humidity.
• Stack units on a hard, level surface that is clean, dry, and away from open doorways and running machinery that could create airborne contaminants.
• Support bolsters that are misaligned, uneven or missing may cause high bending stresses, which could result in permanent warping or damage.
• Materials slated for gluing, laminating or other finishing may need a week or more before coming to temperature and moisture content equilibrium. Such materials should be "conditioned" by separating the panels with clean, dry spacer sticks or by placing panels in a spacing rack to provide good air circulation across all surfaces. Adequate conditioning time should be scheduled into the fabrication process, especially when temperature extremes exist during shipment.
• Temperatures should be kept as close to 70 degrees F (21 degrees C) as possible. Avoid storage in extremely cold or hot temperatures. Warming panels in winter takes just as long as cooling them in summer. While the top few panels may feel comfortable to the touch, the middle ones could be either too hot or too cold. Cold panel and/or cold ambient temperatures will slow the cure rate of laminate adhesives.

Minimizing Warp in Laminated Particleboard and MDF

Warp is defined as the deviation of the geometry of a panel from an initial state of flatness.

• Always select flat panels for substrates. Consider the substrate properties, including stiffness, thickness, linear expansion, and uniformity. These can be evaluated from the manufacturer's specifications or standards. The greater the thickness of the material, the better it will resist moisture-related expansion stresses.
• A cause of warp in laminated panel products is unbalanced panel construction.
• As different materials are rigidly bonded together, moisture content changes may occur. In response to the changes in moisture content, the materials attempt to change dimensions. When that happens, stresses can accumulate. Warp results when these stresses become excessive and are no longer balanced on the two surfaces.
• Selection of laminates and balanced construction go hand-in-hand. The laminates and/or coatings applied to each face of a particleboard or MDF substrate should be similar in properties. Generally, this is best achieved by using the same material to cover both sides of a substrate.
• Unusually moist or dry conditions should be avoided in the laminating and storage environments. The moisture content of wood-based materials and laminates is dependent on the amount of moisture in the air. When these materials are moved from one environment to another, the moisture content changes. Resulting dimensional changes can be substantial.
• It is unlikely that the moisture content of the laminate and the substrate will be in equilibrium with the laminating environment when they are delivered to the laminating shop. Allow sufficient time for the laminate and substrate to adapt to the laminating environment. It can take two or more weeks to reach a satisfactory equilibrium. Seasonal changes and air circulation around the materials will influence the time it takes.
• Once assembled, differences in the expansion or shrinkage characteristics of the laminate and substrate can produce stresses, which cause warped panels.
  Ideally, laminates and substrates should be stored and assembled in conditions similar to the finished product application environment.
• Laminates at one equilibrium moisture content condition should not be applied to particleboard/MDF of a different condition. If they are, as the moisture content equalizes, the particleboard/MDF substrate may expand or contract while the laminate seeks the opposite. When bonded with rigid adhesives, the components cannot move in relation to each other. This creates stresses at the substrate/laminate interface, which can result in a warped panel.
• A well-balanced laminated panel can exhibit temporary warp due to unequal rates of moisture gain or loss by the face and back laminates. However, as soon as the laminates equalize, these stresses diminish, and the panel returns to its flat condition. This ability to equalize and return to the flat condition at any humidity is an important attribute of the balanced panel.