Delamination is the loss of bond between two or more layers of a laminated or composite material. It occurs in glued laminated timber (glulam), plywood, laminated glass, insulation boards, bonded composites and even concrete, and is almost always a sign of damage or a manufacturing defect.
Causes
Delamination develops when a combination of mechanical, thermal and chemical loads exceeds the bond strength between layers. Common causes include:
- Moisture — water penetrates between the layers, expands when freezing and forces the joint open
- Temperature swings — different thermal expansion coefficients of the layers generate shear stresses
- Mechanical overload — bending or impact loads beyond design values
- Poor bond — wrong adhesive choice, insufficient pressing force, or contaminated surfaces
- Ageing — UV radiation and chemical breakdown of the adhesive
Examples by material
Delamination looks different depending on the material:
- Glulam (glued laminated timber) — a continuous horizontal split in the glue line. May significantly reduce load capacity
- Plywood and OSB — bubbles, lifting corners, or peeling of the surface veneer
- Laminated glass — cloudy edges or air pockets between the glass panes and the PVB interlayer
- Sandwich panels — loose facing where the skin separates from the insulating core
- Concrete — flaking of the topping or surface layer, often due to poor bond with the substrate or reinforcement corrosion
Repair
Whether repair is possible depends on the material and the extent of damage:
- Small and localised — re-inject with epoxy or polyurethane, then clamp or press
- Structurally critical — replacement of the element is usually required; for load-bearing beams, consult a structural engineer first
- Pane in an insulating glass unit — no repair; the unit must be replaced
Prevention
- Use the correct adhesive and pressing force as specified by the manufacturer
- Keep the material dry and dust-free before bonding
- Provide external elements with adequate weather protection and UV shielding
- Keep wood products out of direct contact with soil and standing water
Related terms
- Glulam
- Plywood
- Double glazing
- Adhesion
- Wood glue
- Laminated glass
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