The term ‘ply wood refers’ to engineered boards of wood, that are manufactured by gluing multiple very thin sheets (veneers) of wood together. Each adjacent layer is rotated, often by 90 or 45 degrees, so the grain of the wood runs in different directions. This adds strength, reduces shrinkage and expansion, and greatly reduces the chance of the wood splitting when it is screwed through. The number of layers used depends on the final thickness of the board, and it is commonly available from suppliers in the UK in sizes ranging from 3.6 to 25 mm thick. A standard full size board is then 1220 wide by 2440 mm long. Smaller boards are available pre-cut and larger, thicker, and thinner boards can be bought, although generally take a bit more searching for.
The veneers of wood are cut from using a rotary lathe. This machine turns logs against a long very sharp blade that peels the wood in one continuous, or semi continuous roll. This technique of ‘peeling’ logs was invented by a guy called Immanuel Nobel in the mid 18 hundreds. One major positive factor for processing lumber in this way is how efficiently it uses up the wood from the tree, compared to milling it into planks.
All sorts of different types of wood are used to make ply. The choice people make depends on the requirements of the project the wood is to be used for, for example, if it’s for furniture, or a buildings structural construction, and whether its going to be used on the interior or exterior of a building. Sometimes the final outside layer of the wood will be an expensive, slow growing hardwood, such as walnut, cherry or oak. This is a very cost effective way to produce a fine finish for furniture or doors.
Once the veneers have been cut, they are dried and then glue is spread over the sheets. They are then layered and then pressed together while the glue dries. The types of glue used, once again vary, depending on the use of the plywood. Often for exterior used the glue is phenol-formaldehyde based and for interior use it is urea-formaldehyde based. One concern in using plywood is the potential off gassing of the glues chemicals long after production, and the possible health concerns that may arise because of this. Many manufacturers now use a low formaldehyde emitting glue, and some are experimenting with producing plywood using soy based glue. Large suppliers stock plywood that comes with an emissions rating, much like a paint’s Volatile Organic Chemical’s (VOC’s) rating. In my opinion this is something to be aware of.
In the plywood production process, once the sheets have been pressed and the glue has dried, the rough edges of the boards are cut away as they are trimmed to size, and then they are graded and packed, ready to be sent out to the wholesalers.
Plywood is produced all over the world from Finland to India and is classed as an environmentally sustainable building material. Certainly, if the manufacturers are using 100% traceable wood from responsibly managed forests, this section of the production is sustainable. As for the glues used, I will research further, and discuss in another blog post as this is extensive subject in itself and worthy of careful consideration.
There is no doubt that ply wood is a highly versatile building material with multiple uses, that simplifies many woodworking projects, compared to making the same thing from solid wood. If it is used correctly, that is; the right type for the job is selected, it is worked with care and finished suitably, it can be used to produce splendid items that should last for many, many years.