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Finishing

Adhesive bonded corner joints in MDF

Frame joints

Frames for panel or glass doors are often manufactured from wood veneer or decorative foil wrapped MDF rails and stiles. Either butt or mitre corner joints can be used, preferably with dowel or loose tongue reinforcement. The high stability of MDF in varying environmental conditions reduces the risk of appearance defects resulting from movement of the material in the region of the joints. Mitre joints in MDF are more likely to retain their integrity in extreme damp and dry conditions by comparison with the corresponding solid wood joints which are known to be problematical.

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Panel joints

MDF is widely used for the manufacture of boxes and cabinets of different shapes and sizes. The well compacted core of MDF allows considerable scope in the choice of corner joints between the panels. Most of the traditional cabinet making joints ranging from simple mitres to dovetail and comb joints can be used successfully.

General recommendations

The following recommendations apply to adhesive bonded corner joints between MDF pieces.
 

1. The joint parts should be accurately machined. Accurate mitre joint angles are particularly important.
 
2. Sharp cutters should be used to avoid tearing or burnishing the surfaces to be bonded.
 
3. A high solids content adhesive with good gap filling characteristics should be used. Urea formaldehyde (UF) or polyvinyl acetate (PVAC) types satisfying the requirements of EN204 are acceptable, the durability class being determined by the service environmental conditions.
 
4. The two pieces for each joint should be accurately located and held under pressure while the adhesive is setting.
 
5. Grooves machined in MDF to facilitate jointing should be limited to about one third of the thickness of the board. The depth of grooves should be about one half board thickness.
 
6. Dowels or tongues for insertion into holes or grooves should fit easily as tight fitting joints may result in starved gluelines or delamination within the MDF.