| ons |
Formica® decorative high pressure laminates are cellulose-based materials. Like any wood-based materials, they shrink in dry conditions and expand in wet conditions. So always take precautions to prevent stress cracking or adhesive bond failure due to dimensional movement.
Stress Cracking
Stress cracking is the result of stresses set up when the dimensional movements of the laminate and of the substrate to which it is bonded are different in either rate or direction.
In conditions of low humidity caused by central heating, or of localised heating by radiator grilles or hot air vents, shrinkage may occur which can result in cracks at sharp internal corners.
Stress cracking occurs most often when contact adhesives are used: being non-rigid, they allow the laminate to creep.
To reduce the risk of stress cracking, take the following measures.
1. Internal corners of apertures and cut-outs must always be smoothly radiused to as large a radius as possible, with a minimum radius of 5mm. Increase this radius pro rata as the side lengths of the apertures are increased.
2. If sharp internal corners are required as a design feature, form these by butt-jointing panels, not by cut-outs.
3. For on-site bonding where contact adhesive is used, panel widths should not exceed 600mm. Where wider panel widths are required, fabricate these using rigid or semi-rigid adhesives.
4. To minimise dimensional movement, cut the longest dimension of the panel in the length direction of the laminate sheet (parallel with the sanding lines) because laminate movement is approximately twice as great across the sheet width as it is along the length.
5. Avoid the use of contact adhesives in particularly vulnerable areas such as radiator grilles.
6. Fix the panels firmly to prevent any bending or twisting which may cause stress.
7. Pre-condition the laminate, in temperature and humidity conditions similar to those of the final installation, for at least three days before bonding.
8. Use oversized holes to ensure that fixing screws do not impinge on the edge of the laminate.
Adhesive Bond Failure (Bubbling)
The converse situation to stress cracking is adhesive bond failure, commonly known as 'bubbling’. This may occur in conditions of high humidity or wetting if there are weak areas of adhesive bond (usually associated with hand-applied contact adhesives).
If the laminate has been bonded in normal warm and dry conditions using contact adhesive, and the panel is subsequently subjected to high levels of humidity, the laminate will expand. The amount of creep depends on the panel dimensions (the larger the panel, the greater the movement). If there is a weakness in the bond the laminate may lift from the substrate.
To reduce the risk of bond failure, take the following measures.
1. If possible, avoid the use of contact adhesives (particularly hand-applied) with panels to be installed in wet areas or areas of high humidity.
2. If contact adhesives must be used, then panel widths should not exceed 600mm. The adhesive layer must not be too thick; it must be applied evenly to both surfaces; and the whole area must be at the correct tack-level when bonding takes place.
3. To minimise dimensional movement, cut the longest dimension of the panel in the length direction of the laminate sheet (parallel with the sanding lines) because laminate movement is approximately twice as great across the sheet width as it is along the length.
4. Pre-condition the laminate, in temperature and humidity conditions similar to those of the final installation, for at least three days before bonding.
|
