is composed of at least three elements: a face, a back and a core.
Holding these pieces together is the glue line or glue. Each type
of core has a specific use and represents a better value or better
product for the specific use. The most common type of core used
prior to World War II was veneer core.
Veneer Core: Layers of veneer are pressed together in alternating
perpendicular layers balanced on either side of a central core
layer. This type of plywood is more prone to surface irregularities
and defects, but it exhibits greater strength in bending and in
stress than the other core types.
Particle Core or Chip Core: Particle core is produced in large
plants on a continuous press line from wood chips, glue and resins
and then cut up into panels. Its surface is smooth, but some small
voids are always present.
Fiberboard: Fiberboard is the flattest and smoothest core for
plywood. Medium density fiberboard (MDF) makes a superb carrier
for veneer. It has few surface imperfections or voids and is dimensionally
stable and flat.
Lumber Core: Lumber Core is manufactured from thin strips of lumber
glued on edge and covered by a veneer crossband perpendicular to
the cores grain direction. When lighter cores are required
or specific strength in one direction is required, lumber core plywood
is often used.
Fire-Retardant Cores: Fire-Retardant Cores are usually made of
particle core with fire resistant salts added to the chips and
glue when pressed. In many cases, fire rated codes are required
for paneling in entries, lobbbies, and areas of public spaces.
This type of core is weaker and more prone to expansion and contraction
than standard particle core or medium density fiberboard. Fire
rated veneer core is usually less flat and prone to warping. Fire
rated medium density fiberboard is not as available as fire rated
Engineered Wood Cores: Engineered wood is a new type of core utilizing
the strength and lightness of veneer core, but having improved
flatness, rigidity and dimensional stability. The core is made
of linear strips of thick fibrous veneer glued and pressed together
in an irregular pattern.
Water Resistant Cores: Water Resistant Particle Core, Water Resistant
Veneer Core and Waterproof Veneer Cores are available. The Architectural
Woodwork Institute Quality Standards require that all Premium
Grade tops maed for use in wet areas, such as near a sink, be
made from water resistant or waterproof cores.