Plywood is a
sheet material manufactured from thin layers or "plies" of wood veneer
that are glued together with adjacent layers having their wood grain rotated up
to 90 degrees to one another. It is an engineered wood from the family of
manufactured boards which includes medium-density fibreboard (MDF) and particle
All plywoods bind resin and wood
fiber sheets (cellulose cells are long, strong and thin) to form a composite
material. This alternation of the grain is called cross-graining and has
several important benefits: it reduces the tendency of wood to split when
nailed at the edges; it reduces expansion and shrinkage, providing improved
dimensional stability; and it makes the strength of the panel consistent across
all directions. There are usually an odd number of plies, so that the sheet is
reduces warping. Because plywood is bonded with grains running against one
another and with an odd number of composite parts, it is very hard to bend it
perpendicular to the grain direction of the surface ply.
plywoods and lower quality plywoods (see Average-quality plywood photo below
and right) may only have their plies (layers) arranged at right angles to each
other, though many better quality plywood products will by design have five
plies in steps of 45 degrees (0, 45, 90, 135, and 180 degrees), giving strength
in multiple axis. The highest quality specialty plywoods often have plies at 30
degrees (0, 30, 60, 90, 120, 150, and 180 degrees) in seven layers, or have
nine layers with two layers of 45 and 135 degrees in the sandwich. The smaller
the step rotations the harder it is to manufacture, increasing manufacturing
costs and consequently retail price.
Types of plywood
Different varieties of plywood exist for different
plywood Hardwood plywood
plywood (overlaid plywood)
Grading rules differ according to
the country of origin. Most popular standard is the British Standard (BS) and
American Standard (ASTM). Joyce (1970), however, list some general indication
of grading rules:
A Face and
back veneers practically free from all defects.
practically free from all defects. Reverse veneers with only a few
knots or discolorations.
A/BB Face as A but
reverse side permitting jointed veneers, large knots, plugs, etc.
B Both side
veneers with only a few small knots or discolorations.
B/BB Face veneers with only a few
small knots or discolorations. Reverse side permitting jointed veneers, large
knots, plugs, etc.
sides permitting jointed veneers, large knots, plugs, etc.
well glued only. All broken knots plugged.
knotholes, cracks, and all other defects permitted.
Face as BB, back as CC. BB as
very little knots of less than 1/4 inches, slight BB/CC discoloration, no
decay, split and wormholes mended skillfully, matched colors,
blister, no wrinkle. Most popular choice for most applications.
Plywood is used in many
applications that need high-quality, high-strength sheet material. Quality in
this context means resistance to cracking, breaking, shrinkage, twisting and
Exterior glued plywood is
suitable for outdoor use, but because moisture affects the strength of wood,
optimal performance is achieved in end uses where the wood's moisture content
remains relatively low. On the other hand, subzero conditions don't affect
plywood's dimensional or strength properties, which makes some special
Plywood is also used as an
engineering material for stressed-skin applications. It has been used for
marine and aviation applications since WWII. Most notable is the British de
Havilland Mosquito bomber, which was primarily made using a moulded sandwich of
two layers of birch plywood around a balsa core. Plywood was also used for the
hulls in the hard-chine Motor Torpedo Boats (MTB) and Motor Gun Boats (MGB)
built by the British Power Boat
Company and Vosper's. Plywood is currently successfully used in stressed-skin
applications. The American designers Charles and
Eames are famous for their
plywood-based furniture, as is Finnish Architect Alvar Aalto and his firm
Artek, while Phil Bolger is famous for designing a wide range of boats built
primarily of plywood.
Plywood is often used to create
curved surfaces because it can easily bend with the grain. Skateboard ramps
often utilize plywood as the top smooth surface over bent curves to create
transition that can simulate the shapes of ocean waves.
Softwood plywood applications
Typical end uses of spruce plywood are:
Floors, walls and roofs in home constructions
Wind bracing panels
Vehicle internal body work
Packages and boxes
There are coating solutions
available that mask the prominent grain structure of spruce plywood. For these
coated plywoods there are some end uses where reasonable strength is needed but
the lightness of spruce is a benefit e.g.:
Concrete shuttering panels
Ready-to-paint surfaces for constructions
Hardwood plywood applications
Phenolic resin film coated (Film
Faced) plywood is typically used as a ready-to-install component e.g.:
Panels in concrete form work systems
Floors, walls and roofs in transport vehicles
Floors subjected to heavy wear in various
buildings and factories
("Wire" or other styles of imprinting available for
Birch plywood is used as a
structural material in special applications e.g.:
Wind turbine blades
Insulation boxes for liquefied natural gas (LNG)
Smooth surface and accurate
thickness combined with the durability of the material makes birch plywood a
favorable material for many special end uses e.g.:
High-end loud speakers
Supporting structure for parquet
Signs and fences for demanding outdoor advertising
Tropical plywood applications
Tropical plywood is widely
available from the South-East Asia region, mainly from Malaysia and Indonesia.
Tropical plywood boasts premium quality, and strength. Depending on machinery,
tropical plywood can be made with high accuracy in thickness, and is a highly
preferable choice in America, Japan, Middle East, Korea, and other regions around
Laminated veneer lumber (LVL)
In woodworking, veneer
refers to thin slices of wood, usually thinner than 3 mm (1/8 inch), that
typically are glued onto core panels (typically, wood, particle board or
medium-density fiberboard) to produce flat panels such as doors, tops and
panels for cabinets, parquet floors and parts of furniture. They are also used
in marquetry. Plywood consists of three or more layers of veneer, each glued
with its grain at right angles to adjacent layers for strength. Veneer beading
is a thin layer of decorative edging placed around objects, such as jewelry
boxes. Veneer is also used to replace decorative papers in Wood Veneer HPL.
Veneer is also a type of manufactured board.