What is Plywood?
Plywood is an extremely versatile material that is used for a wide range of construction tasks. From roofing and flooring, to use in furniture and much more, plywood is an affordable and reliable material that many industries rely on every day. In this article we explain more about what plywood is, the different types available and what the best kind is, helping you to have a better understanding.
What is plywood?
Plywood has been in production since the 1850s, when it was initially used to make tea chests. Today it remains one of most popular construction materials around. It is formed by gluing layers of wood called veneers together to create a solid sheet. The grain of each alternating layer typically runs at right angles to each other, this spreads any stresses in equal directions making the panel extremely strong.
Sheets are usually made up of odd numbers, such as three or five ply. This helps to stabilise the forces on either side of the timber’s core so the sheet remains stable. Each layer should be of a similar thickness and wood species, although the core layer can be thicker. There are some instances where the above properties are deliberately altered to produce a panel with specific characteristics.
What types of plywood are available?
When you start searching for the right type of plywood for your project, the large amount of choice can seem quite overwhelming. Some of the most common include:
Usually made from Douglas fir, cedar, redwood, pine or spruce, this type is usually used for construction, such as floor joists and roofing. Often referred as coniferous plywood, it's use is extensive particularly in North America where timber frame dwellings are prevalent.
Tropical Hardwoods such like meranti, oak, beech and mahogany and eucalyptus wood are often used for this type of plywood often due to its strength. Great for wall structures and heavy-duty flooring and also where a high quality finish is desired due to the finer grain provided by the hardwood outer veneers.
This is graded to meet British Standard BS 1088 and Marine Plywood is great for environments where it may be exposed to moisture for long periods. Marine plywood has an exterior quality glue-line and ensures that veneers are free from splits, this means no core gaps (voids) will be present when the panel is finished. The lack of core gaps prevents water pooling and subsequent and premature delamination.
Also known as aircraft plywood, it is one of the highest grades available ensuring an incredibly strong but light panel. Several thicknesses are available as with surface veneer qualities (grades) typically these plywoods are made with birch as this provides the best available strength and quality veneers needed to produce such a high quality product. These very thin and finely veneered plywoods are also used widely in Saddle Manufacture (Saddlery).
Concrete shuttering plywood:
On concrete formwork projects concrete shuttering plywood is ideal panelling for both curved and flat surfaces. Good quality ply will ensure minimal deflection and high levels of durability for multiple re-uses if needed. Now rarely used 'bare' douglas fir plywood was oiled (mould oil) to prevent it sticking to the cured concrete. Nowadays form-working plywoods have a phenolic paper face bonded to them, this provides a fine and smooth finish to the poured concrete and guarantees multiple uses (pours) for each panel, keeping the cost down.
Why is BS 1088 important?
We mentioned above that marine plywood is certificated to BS 1088. This British Standard applies to plywood that has been produced with untreated tropical hardwood veneers, with a specific level of resistance to fungal attack. Weather Boil Proof (WBP) glue is then used to bond the plies and no core gaps can be present in the veneers.
These high standards are important as marine plywood is able to withstand exposure to moisture for long periods of time, and are used in the construction of boats and ships. It can also be used for a wide variety of other applications that require high levels of performance and a long service life. Regardless of the project it is used in, before application all ply faces and edges must be primed and sealed.
What is the best way to cut plywood?
To ensure the best possible cut, use an electric saw to cut through plywood, as a hand-held saw is likely to lead to a break out of the face veneer on the down stroke. The steps below provide a basic outline:
- To cut the plywood use a crosscutting blade that has an alternate top angle. If you also have a crosscutting blade with triple chip teeth this will also help to produce a great cut. The more teeth the blade has, the less splintering there will be.
- Place a waste board below the plywood you want to cut, as this will reduce any breakout of the plywood on the other side.
- Before using the blade mark the cutting points using a marker. This will ensure you maximise the board available to you and reduce wastage.
- Always try to work with the ‘best’ face up.
What is the best kind of plywood?
While there are a number of different types of plywood available, Finnish Birch plywood is generally considered as being the finest quality plywood in the world but often has the poor availability and high price to match. Other Baltic countries produce birch plywood and in most cases this is the best balance of quality and price available.
Baltic birch comes from the Baltic States such as Latvia and Estonia, birch is also shipped from Russia. It is made from birch plies only, different grades are available which describe the quality of the face veneer and sometimes the makeup of the core veneers.
There are a number of reasons why Birch plywood is preferred, including:
- Birch veneers are often an even thickness they provide a very strong plywood which can withstand significant loading.
- No voids in the core and total glue coverage provide a low failure rate.
- High screw holding strength
- Smooth and consistent face veneer grades
- Long and cross grained sheets available
- Aesthetic appeal, architecturally elegant with an attractive figure and grain