| Understand construction – Plywood as a building material is very widely used due to its many useful properties. It is an economical, factory-produced sheet of wood with precise dimensions that does not warp or crack with changes in atmospheric moisture. Ply is an engineered wood product made from three or more ‘plies’ or thin sheets of wood. These are glued together to form a thicker, flat sheet. The logs used to make plywood as a building material are prepared by steaming or dipping in hot water. They are then fed into a lathe machine, which peels the log into thin plies of wood. each ply is usually between 1 and 4mm thick. USES OF PLYWOOD AS A BUILDING MATERIAL Plywood has a huge range of uses within the construction industry. Some of its most common uses are: To make a light partition or external walls to make formwork, or a mold for wet concrete to make furniture, especially cupboards, kitchen cabinets, and office tables part of flooring systems for packaging to make light doors and shutters |
HOW PLY IS MADE
WHICH WOOD IS PLY MADE OF?
Plywood is manufactured from softwood, hardwood, or both. The hardwoods used are ash, maple, oak, and mahogany.Douglas fir is the most popular softwood for making plywood, although pine, redwood, and cedar are common. Composite plywood can also be engineered with a core of solid timber pieces or particleboard, with a wood veneer for the face and back. Composite plywood is preferable when thick sheets are required.
Additional materials can be added to the face and back veneers to improve durability. These include plastic, resin-impregnated paper, fabric, Formica, or even metal. These are added as a thin outer layer to resist moisture, abrasion and corrosion. They also facilitate better binding of paint and dyes.
PROPERTIES
High Strength: Plywood has the structural strength of the wood it is made from. This is in addition to the properties obtained from its laminated design. The grains of each veneer are laid at 90 degree angles to each other. This makes the whole sheet resistant to splitting, especially when nailed at the edges. It also gives the whole sheet uniform strength for increased stability. Furthermore, plywood has a higher strength to weight ratio as compared to cut lumber. This makes it ideal for flooring, webbed beams, and shear walls.
Flexibility: Unlike cut timber, plywood can be manufactured to fit every requirement. The thickness of each veneer can vary from a few millimeters to several inches. The number of veneers used also ranges from three to several, increasing the thickness of the sheet. The extra layers add more strength to the plywood. Thinner veneers are used to increase flexibility for use in ceilings and paneling.
Chemical resistance: Plywood treated with preservative does not corrode when exposed to chemicals. This makes it suitable for chemical works and cooling towers.
Impact resistance: Plywood has high tensile strength, derived from the cross lamination of panels. This distributes force over a larger area, reducing tensile stress. Plywood is therefore able to withstand overloading by up to twice its designated load. This is critical during short-term seismic activity or high winds. It is also useful in flooring and concrete formwork.
TYPES OF PLYWOOD
Structural plywood: Used in permanent structures where high strength is needed. This includes flooring, beams, formwork, and bracing panels. It can be made from softwood or hardwood.
Internal plywood: This has a beautiful finish, for non-structural applications like wall paneling, ceilings, and furniture.
GRADES OF PLYWOOD
Plywood grades are determined by strength, discolorations, surface defects, and resistance to moisture, among other properties. The quality of surface veneer, type of wood, and strength of adhesive, will then be allocated a particular rating. Each rating will determine the type of application the plywood is suited for.
Plywood grades are N, A, B. C, and D. The D grade has several surface defects such as graining and knotting, while the N grade has few of these. An “interior C-D” rating for example, indicates the plywood has a grade C face, and a grade D back. It also means the adhesive is suited for interior applications.