Plywood is a versatile building material made from thin layers, or “plies,” of wood veneer glued together. It is a very durable material that provides an excellent foundation for building, so it is used in a variety of projects. But, as with any building material, it has both advantages and disadvantages that should be understood before use.
Different types of plywood exist for a variety of building functions, each usually composed of different materials.
Usually made of cedar, spruce, fir, pine, or redwood, softwood plywood is the most common type used for construction and industrial purposes. This type can vary in the thickness and number of its plies when being used in different projects. Thinner plywood is used, for example, in roofing, while something thicker will be put down for subflooring.
Hardwood is a stronger kind of plywood made from angiosperm trees that are valued specifically for its strength, surface hardness, and resistance to wear and tear.
Mixed species of tropical wood make up this low-cost variety of plywood. It’s generally considered superior to softwood plywood due to its higher quality, density, and strength, and the evenness of its layers. In many countries around the world, this type is in wide use.
High strength, aviation-grade plywood is made from mahogany or birch and uses adhesives that are more resistant to higher levels of heat and humidity so it can retain its quality even in harsher conditions.
This type is usually faced with some kind of hardwood, such as ash, oak, birch, maple, rosewood, or mahogany, and is used for things like cabinetry, furniture, and fixtures.
Formed from a very thin central ply and two outer pieces, flexible plywood is specifically designed with curved pieces in mind. This type is made to bend and is usually glued together once it is formed into its final shape, for a stiff finished piece.
Marine plywood is used in the construction of docks and boats, and it usually costs more than standard plywood due to the more durable face and core it must have to resist humid and wet conditions. Usually, marine plywood veneers are made from tropical hardwoods and attached with water and boil-proof glue.
The layers that make a sheet of plywood are intentionally glued together at alternating right angles. This is what gives it both strength and durability. This cross-graining also reduces the chances of the wood splitting when nailing at the edges, and it makes the wood resistant to warping, cracking, and twisting. The way plywood is made also ensures a consistent strength across the entire length of the wood.
In addition to its strength, plywood is less expensive than similar boards made of full wood species, which makes it an ideal construction planking material.
While plywood's layered property has many advantages, it also makes the wood porous, and susceptible to water damage if exposed to leaks over time. Plywood becomes heavy when wet and should be covered if left outside to reduce the risk of absorption.