Plywood is an extremely versatile building material which covers a wide range of applications from wall sheathing to floors and roofs.
The raw material used in the manufacture of plywood consists of coniferous wood (softwood), hardwood or tropical hardwood. Sometimes a combination of different species can be used. Plywood is made up of a number of layers, called plies which are glued together.
Firstly, the logs are peeled into layers called veneers. These layers are then glued together one by one, cross-banded, which means the grain direction is alternated each time. By bonding the layers cross-banded the plywood will be a lot stronger than a similarly sized board cut from a single tree. Good plywood products able to withstand extreme weather conditions, are assured by using phenolic formaldehyde resin in the glue.
Plywood can be used structurally or for non-structural applications depending on its CE certification. The finish quality of face veneers varies enormously; some have attractive grains while others can have a large number of knots depending on the species and grading.
Certain types of Plywood can be used for differing requirements. However to provide the desired performance and service life, they must be correctly specified, detailed, installed and maintained. The key point to remember is to find out what the plywood will be used for and to then offer the best product for the particular application.
There are many types of plywood available and differences are determined by the species, the country of origin, the glue type and the construction.
The main size which plywood comes in is 2440 x 1220 mm (8’ x 4’) and in various thicknesses.
Sheathing/Shuttering Plywood is predominantly used for structural use. Although moisture resistant to a degree the faces of this material are not finished with a decorative veneer and it may have large knotholes that make it unsuitable where a quality finish is required.
WBP stands for “Water Boiled Proof”. This is an old British Standard term although people still refer to it. The new terms are EN 636-(1, 2, 3) and EN 314-2 (Class 1, 2, 3), looking at the species of the wood and the glue-line together. See ‘Plywood Specifications’ document which provides explanation on these terms.
The new European term for ‘WBP’ EN 636-3 and EN 314-2 Class 3 can be exposed to weather, water and moisture for a long period without delamination. However does require additional protection (paint or varnish) to protect its outer veneer.
Plywood for use in formwork can also be supplied with a phenolic film face or another option is MDO plywood (medium density overlay), which both give different finishes.
FILM FACED PLYWOOD
HARDWOOD THROUGHOUT PLYWOOD
HARDWOOD FACED POPLAR CORE PLYWOOD
It is very important to remember that ALL plywood must be sealed on all edges and faces with oil-based paint before being exposed to the elements.
By using plywood it is a good way to help reduce the increase of global warming because wood is a renewable resource. Trees when growing absorb carbon dioxide from the air giving out the oxygen we breathe in.
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