The smooth surface of MDF provides a good substrate for the application of wood veneer as used for the manufacture of traditional furniture and interior panelling. The close thickness tolerance of ±0.2 mm for boards up to 30 mm thickness and ±0.3 rum for boards thicker than 30 mm, as specified in the EM13 Industry Standard, ensures uniformity of pressure over all the panels in a press load. Manufacturers finish sanding of boards using 100 or 120 grit ensures good adhesion and freedom from showthrough defects.
Satisfactory bonding can be achieved using urea formaldehyde (UF) or cross linking polyvinyl acetate (PVAC) adhesives and the pressing conditions which have been developed over many years for use with particleboards.
Typical pressing conditions are as follows:
80 - 120 g/m2
350 - 600 kN/m2
70 - 100°C for multidaylight pressing
100 - 130°C for single daylight pressing
2 - 4 min for multidaylight pressing
30 - 60 s for single daylight pressing
MDF is normally supplied at 8 ±3% moisture content. The veneers should normally have moisture contents in the range 8 to 12%, with lower moisture contents recommended for the more exotic veneers such as curl mahogany and burr walnut and for panels intended for use in the particularly dry conditions associated with continuous central heating.
The MDF surfaces should be free from defects and brushed to remove any dust deposits which might show through the veneered surfaces.
Facing and backing veneers should have approximately equal thicknesses and moisture contents at the time of bonding to ensure flatness of the veneered panels.
After removal from the press, the veneered MDF panels should be stacked on a flat surface or on close spaced bearers of equal thickness and allowed to cool for a minimum of 8 hours before further processing.