Solid wood countertops are natural products made of wood; wood is a living material and the more moisture receives, the more the wood countertop will expand. The wood used in solid wood worktops has been previously kiln dried to a humidity level of 6%. Therefore it’s important that the worktop is not exposed to a constant high level of humidity. Normally the humidity level in kitchens is approximately 50-70%.
The proper way of installing a solid wood top is using metal fittings along the cabinet box.
The solid wood top must be attached to the cabinet box using only wood screws and washers. It is not recommended at all to glue the top on the cabinet box; the top and the box expand and contract at different rates. Therefore cracks might eventually appear, most probably on the cabinets’ surface.
The metal fittings must be uniformly distributed throughout the length of the top; space them at a 1′ – 1.5′ distance from each other. Across the width, the top is usually fixed to each metal support with three screws, one in the middle, one toward the front edge and one toward the rear edge. The supports must be perfectly leveled; otherwise, tensions can develop in the wood, leading to warping, cupping, or cracks.
We recommend pre-drilling the screw holes into the wood countertop, in order to avoid cracks and splits. For the same reason, it is a good idea not to over tighten the screws. The finishing will considerably diminish the extent of such movements, but will not eliminate them altogether. Due to the panel’s laminated structure, the lengthwise movements are insignificant. Therefore the installer should pay attention to the movements occurring across the panel’s width. In order to prevent the development of inner tension, the holes in the metal fittings should be elongated in the direction of movement.
When exposed to normal humidity levels – 50-60% – the worktop’s width will expand by 1/12”-1/24”. But when exposed to a level of 80-90%, this measurement may expand by up to 1/2″ or even more for some wood. Therefore, when the rear edge of the countertop is installed against a wall, the wall might restrict the top’s natural movements. This can lead to undesired tension in the wood. To avoid this, you can allow a 1/4”-1/2” joint between the wall and the countertop edge and caulk it with a thin bead of acid-free silicone.
Additionally, you can firmly fix the rear edge to the metal supports underneath. This allows the natural movements to occur at the expense of the opposite edge.
In this case, the holes in the metal fittings corresponding to the rear edge will be no larger than the diameter of the screw, while the holes corresponding to the middle section and the front edge will be elongated.