By Abhijit Phadke
This is a detailed article about plywood, that covers various aspects of plywood such as, what it is, How its made, its different types and uses, and how it compares with other wood products.
So, let's begin with:
What is plywood?
Plywood is an engineered wood product, and has many varied applications. It is most commonly used for making the furniture that we use in our homes and offices, and also for other applications such as in building construction, and for doing the woodwork in boats and ships.
Composition of plywood:
Plywood is made from several thin layers of wooden veneers stacked over one another. These veneers, called plies, are firmly glued to each other so that they don't come apart easily.
The number of plies in every plywood sheet is usually an odd number, such as 3-ply, 5-ply, 7-ply etc.
While stacking the veneers over one another, it is ensured that the grain direction of the plies in adjacent layers is perpendicular to each other. Because of this the plywood board becomes strong in both directions.
How plywood is made:
The veneers, which are thin slices of wood are obtained from logs of trees. The logs are mounted on a lathe machine, and are rotated about their longitudinal axis, while a cutter peels off thin layers from the log (Somewhat similar to the way we peel layers from vegetables).
Glue is applied to all these peeled slices of wood veneers (plies) using glue spreader machines, and the plies are placed one upon the other. The stack then goes into a hot press machine, which firmly presses the veneers together and forms a strong bond between the individual plies so that they do not come apart. Thus a plywood sheet or board is made.
Adhesives used in plywood:
There are two kinds of glue used. One is UF (Urea Formaldehyde) resin, and the other one is 'Phenol Formaldehyde' resin. Phenolic resins are considerably better than UF resins because they can form a stronger bond between the plies. (Phenol is the material from which all plastics are made).
Types of plywood:
The three most well-known types are:
It is Interior grade and meant for indoor use.
Made using UF resins.
Used in home and office furniture.
It is Moisture resistant (MR grade) but it is not waterproof.
Exterior grade for outdoor use.
Made using phenolic resins.
Used in kitchen and garden furniture.
It is adequately waterproof, and known as BWR (Boiling water resistant) plywood.
Used for marine applications, such as for boats and ships.
Made using undiluted phenolic resins.
Very strong and very waterproof.
Apart from these 3 well-known types of plywood listed above, there are other kinds such as flexible plywood that can be bent, fire-retardant plywood that delays catching fire, structural plywood that is used for structural building work, and film-faced concrete shuttering plywood that is used for making the wooden moulds into which concrete is cast.
Plywood Sizes and Thickness:
The most commonly available plywood size in the market is 8' x 4' (8 feet by 4 feet), and the use of 18 mm/19 mm sheets is very common in the making of furniture.
I have listed the standard plywood thickness and sizes available in India, in another article, whose link you will find at the end of this post. There are also other information articles about plywood listed towards the end of this post.
Popular uses of plywood:
For making plywood furniture such as tables, chairs, wardrobes, single and double beds, kitchen cabinets etc.
Also in some cases of wooden roofing and wooden flooring.
Marine plywood is used for building the decks and doing the other woodwork in boats and ships.
Structural and Shuttering plywood is used in the industrial and building construction industry.
Apart from this there are hundreds of other uses of plywood such as for making sports equipment (table tennis racquets and tables), musical instruments (such as guitar) and many other things. Its a very versatile material that is easy to work with and hence has numerous applications.
With Solid wood:
Good quality natural solid woods such as teak wood are markedly better than plywood, not only in terms of aesthetic appeal and beauty, but also in terms of strength. That said plywood is easier to work with and costs lesser.
With Particle boards and MDF:
Particle boards are made from particles of wood, while plywood is made from wood veneers. Plywood is definitely better than particle boards in terms of durability, strength, and resistance to water. But it is also costlier compared to particle boards.
MDF (Medium density fibreboards) are much better than particle boards, but good quality plywood is still generally considered to be the stronger, more durable and better option.
Particle boards and MDF furniture are ready-made products that you can buy and start using straight away, whereas plywood furniture will usually be custom-made by carpenters to suit your requirements.
With Blockboards/Blockwood sheets:
Blockboards have rectangular wooden blocks inside them. These blocks they are arranged end-to-end, and covered with a layer of ply on either side. From the outside they look similar to plywood though their core is entirely different.
Plywood is stronger since it is usually made from logs of hardwood trees, while the blocks of the blockboard are usually softwood. However in cases where lengthy pieces of wooden boards are required, blockboards are better since they have lesser tendency to bend in the middle.
Plywood sheets are costlier compared to blockboards.
What is plyboard? Is it any different from plywood?
In India, plywood sheets as well as block boards are often marked as 'Plyboard', or 'Ply & board' or in some cases as 'Plywood & Blockboard'. What you see the term 'plyboard' what it generally means is that the company that has made that particular sheet, is into the business of making plywood as well as blockboards. So, the word 'plyboard' is just a naming convention.
Countries and Naming Conventions:
The naming conventions followed in the plywood industry vary from one country to another. For example, Exterior grade waterproof plywood in India is known as BWR (Boiling Water Resistant), while in the US and Canada it is known as WBP (Weather and Boil proof). In a like manner, flexible plywood is also known by other names such as Bendy ply.
Wood used for making plywood:
There are two kinds of wood, hardwood and softwood. Hardwood is obtained from deciduous trees such as teak and rosewood (sheesham)and is the stronger and more durable. Much of the good quality plywood used for making furniture is made from hardwood, however softwood such as mango wood or pine wood can also be alternatively used in its making. In India, plywood made from Gurjan wood, which is a good quality hardwood is very popular.
Demand and Supply:
Forests and trees are a limited resource. Though new trees are continuously planted as a replacement for all the wood that is consumed by mankind, it takes several long years for a tree to reach its full growth. Hence wood and subsequently plywood has steadily been becoming costlier over the years.
This is the main reason that particle boards and MDF has gained in popularity in the recent few years. These are made from very fine particles of wood such as sawdust and wood fibres, which are often a waste byproduct of other wood processes, and hence furniture can be made at a much cheaper cost using these new kinds of engineered woods.
Ecological concerns related to the plywood industry:
There are two aspects to this.
The first ecological concern is about the ever-dwindling forest reserves, which means that wood has to be used sparingly, without depleting the forest cover that is so essential for the well-being of mankind. Wood harvested from managed plantations is one of the ways in which this concern is being addressed.
The other concern is about the health hazards of the adhesives that are used in the making of plywood. Formaldehyde emissions are considered to be carcinogenic in high concentrations, and can pose a health risk for humans. Plywood makes use of Urea formaldehyde and Phenol formaldehyde glues, and manufacturers have to ensure that the formaldehyde emissions are kept under control.
Ways of decorating plywood:
Unlike natural solid wood, plywood is not a very beautiful looking material. It is strong, but it usually needs to be decorated in some way or the other so that it looks good as well. The most common ways of decorating plywood are listed below.
Painting - This is one of the cheapest ways to decorate plywood. You can use any wood colour of your choice for this purpose.
Staining - This also adds colour to the plywood, but in a way that the underlying grain pattern can still be seen. Painting on the other hand forms a thicker coat that covers the plywood grain entirely.
Laminating - Decorative laminates can be glued over the plywood surface to make it look attractive. These decorative laminates are made from papers saturated with phenolic and melamine resins, and are hard, brittle, water-resistant and scratch-resistant. These decorative laminates are available in various shades, colours, designs, textures and patterns, and are the top choice for decorating plywood. Laminated plywood not only looks good, it also helps to protect and to increase the life of the plywood sheet.
Veneering - Very thin slices of veneers obtained from a better looking wood (e.g. teak, oak, maple, cherry wood etc.) can be glued over the faces of the plywood to make it look more beautiful. Good quality and rare wood veneers are however much costlier compared to decorative laminates.