Plywood is the most widely recognized engineered wood-based panel. It’s used to construct floors and walls, to form concrete, roofing and other building construction works. It’s often chosen for its ability to withstand a lot of stress and full weather exposure for short periods. Plywood can also be used for decorative purposes, including exterior cladding, doors, and interior cabinetry, shelves, and furniture.
What was once considered primarily a construction material has now become the material of choice for furniture design. This can be partially attributed to a wider availability of CNC machines in workshops and the rise of CNC hobbyists. The popularity of plywood furniture has surpassed the popularity of MDF furniture, as Google Trends suggests.
The spike in the graph on March 2020 is due to Covid-19 lockdowns, but as the graph shows plywood furniture continues to trend upwards.
Another contributing factor is the rise of Open Design platforms like opendesk.cc where plywood is the material of choice. Global brands such as Nike, Google, and WeWork are just a few of multinational corporations that embraced plywood furniture to furnish their offices.
But how is plywood made?
Plywood is a wood-based material made of veneers or thin wood layers bonded perpendicularly to each other with a synthetic resin. This resin is made by combining formaldehyde and urea in most cases even though sometimes phenolic glue is used too.
The alternation of the grain (cross-graining) has important benefits. It reduces the tendency of wood to split when nailed. Additionally, it reduces expansion and shrinkage, providing improved dimensional stability, and it makes the strength of the panel consistent. Usually, there are an odd number of plies, which makes the sheet balanced reducing warping.
The manufacturing process of Plywood
The trees that are used to make plywood sheets are generally smaller in diameter. They are typically grown in areas owned by the plywood companies, and are managed to maximize tree growth, and minimize damage from fire.
Plywood can be made from softwoods or hardwoods. Common softwoods used in plywood include pine, cedar, redwood, and spruce but the most commonly used is Douglas fir. For hardwoods, plywood is created using oak, mahogany, teak, maple, ash, or birch.
Selected trees are marked to be cut down, or felled. The felling is done with chain saws or with hydraulic shears mounted on vehicles called fellers that remove the limbs. Logs are dragged out of the forest with vehicles called skidders. The logs get cut to length, and loaded on trucks for the trip to the mill, where they are stacked in long log decks.
Once the logs arrive at the mill they are placed on a conveyor that brings them through a machine that removes the bark. This is done with grinding wheels or high-pressure water, while the log is slowly being rotated. The log is then rotated while a blade is pressed to it, causing a layer of wood to peel off. It looks similar to a sheet of paper coming off a roll.
The layers are graded, glued together, and then baked in a press at a temperature of at least 284 °F (284 °C). While baking a pressure of up to 280 psi is added to form the plywood panel. Plywood can range quite substantially in size but usually is glued in sheets of 8×4 feet (2400mm x 1200mm). The thickness can be anywhere from 0.15 inches (4mm) all the way to 3.0 inches (75mm), but most commonly falls in the range of 0.25 inches (6mm) to 0.75 inches (18mm) thick.
There are several grades of plywood ranging from grade A “defect free” to D with knots that are not filled.
- A-grade is the highest quality, and very rare.
- B-grade has minor flaws
- C-grade has visible knots up to 1.5″ (38mm) in diameter.
- D-grade Can have flaws and knots up to 2.5″ (65mm) in diameter.
Feature Photo Credit: Archives New Zealand CC by 2.0 Image has been cropped