What is plywood?
Plywood is an assemblage of wood veneers bonded together to produce a flat sheet. While it can be tailored to suit an extensive range of applications, the normal product consists of at least 3 plies, with the grain in the alternate plies running at right angles.
Plywood is a 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 board (chipboard).
The basics you need to know about Plywood is that it’s a sheet material which is brought to life by combining layers of wood veneer, which are glued together. Each adjoining layer is rotated up to 90 degrees in a process we call cross-graining. Why is this done? Well, the major reason is that it gives the product super strength. Thanks to cross-graining Plywood is able to resist splitting when nailed at the edges, minimise expansion and shrinkage and bump up its stability. Similarly, when cross-graining an odd number of layers will be used. This provides us with a balanced sheet that won’t easily warp.
The core layers are also crucial to the strength of Plywood. These layers increase the separation between the outer layers where stress is at its highest, meaning its ability to fight back against bending is raised dramatically. Thanks to this method of design larger sheets of Plywood can be created while still handling similar loads by increasing the thickness. However, it’s also perfect for smaller sized sheets too.
The rotation of the direction of each layer’s grain – called cross-graining – is often 90 degrees (a right-angle). This means that every other layer has its grain oriented in the same direction, with a layer oriented at 90 degrees in between. However, rotation can be as little as 30 degrees. In some thicker plywood, seven layers may be arranged successively at 0, 30, 60, 90, 120, 150 and 180 degrees).
A brief history of plywood
Wooden articles made in Ancient Egypt around 3500 BC are the earliest known instances of the use of plywood. They were made from sawn veneers glued together crosswise in a very similar way to today’s plywood.
China, England and France
Around 1,000 years ago, the Chinese shaved wood and glued it together for use in furniture.
The English and French made panels on the general principle of plywood in the 17th and 18th centuries.
Plywood is strong, generally quite resistant to impact damage, comparatively light and relatively easy to cut and “work” with tools.
It excels as a sheet material to form or cover large, flat-sided, sloping or level shapes like walls, floors, some types of roof and large containers.
Useful for intricate work
Some types of plywood are useful for more intricate work such as model-making, wooden jig-saw puzzles and small boxes.
Plywood offers all the inherent advantages of the parent wood plus enhanced properties in its laminated structure.
High impact resistance
Being a wood based material, plywood has the ability to accommodate the occasional short-term overload; up to twice the design load. This is useful where seismic activity or cyclonic winds can occur. This property is also effective when used as construction flooring or as concrete formwork. Plywood’s laminated structure distributes loads from impact over a larger area on the opposite face, which effectively reduces the tensile stress.
Surface dimensional stability
The cross laminated construction of plywood ensures that plywood sheets remain relatively stable under changes of temperature and moisture. This is especially important in flooring and formwork construction where moisture exposure is very likely.
High strength to weight ratio
With high strength and stiffness to weight ratios, plywood is very cost effective to use in structural applications such as flooring, shearwalls, formwork and webbed beams.
The panel shear of plywood is nearly double that of solid timber due its cross laminated structure. This makes plywood a highly effective material to use in gussets for portal frames, webs of fabricated beams and as bracing panels.
Plywood does not corrode and can be used in chemical works and cooling towers as a cost-effective, durable material when preservative treated.
Types of plywood
Softwood plywood is usually made either of cedar, Douglas fir or spruce, pine, and fir (collectively known as spruce-pine-fir or SPF) or redwood and is typically used for construction and industrial purposes.
The most common dimension is 1.2 by 2.4 metres (3 ft 11 in × 7 ft 10 in) or the slightly larger imperial dimension of 4 feet × 8 feet. Plies vary in thickness from 1.4 mm to 4.3 mm. The number of plies—which is always odd—depends on the thickness and grade of the sheet. Roofing can use the thinner 5⁄8-inch (16 mm) plywood. Subfloors are at least 3⁄4 inch (19 mm) thick, the thickness depending on the distance between floor joists. Plywood for flooring applications is often tongue and groove (T&G); This prevents one
board from moving up or down relative to its neighbor, providing a solid-feeling floor when the joints do not lie over joists. T&G plywood is usually found in the 1⁄2-to-1-inch (13 to 25 mm) range.
Hardwood plywood is made out of wood from dicot trees (Oak, Beech and Mahagony) and used for demanding end uses. Hardwood plywood is characterized by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel-carrying capacity. Hardwood plywood has excellent surface hardness, and damage- and wear-resistance.
Tropical plywood is made of mixed species of tropical timber. Originally from the Asian region, it is now also manufactured in African and South American countries. Tropical plywood is superior to softwood plywood due to its density, strength, evenness of layers, and high quality. It is usually sold at a premium in many markets if manufactured with high standards. Tropical plywood is widely used in the UK, Japan, United States, Taiwan, Korea, Dubai, and other countries worldwide. It is used for construction purposes in many regions due to its low cost. However, many countries’ forests have been over-harvested, including the Philippines, Malaysia and Indonesia, largely due to the demand for plywood production and export.
High-strength plywood, also known as aircraft plywood, is made from mahogany, spruce and/or birch using adhesives with an increased resistance to heat and humidity. It was used in the construction of air assault gliders during World War II and also several fighter aircraft, most notably the multi-role British Mosquito. Nicknamed “The Wooden Wonder” plywood was used for the wing surfaces, and also flat sections such as bulkheads and the webs of the wing spars. The fuselage had exceptional rigidity from the bonded ply-balsa-ply ‘sandwich’ of its monocoque shell; elliptical in cross-section, it was formed in two separate mirror-image halves, using curved moulds.
Structural aircraft-grade plywood is most commonly manufactured from African mahogany, spruce or birch veneers that are bonded together in a hot press over hardwood cores of basswood or poplar or from European Birch veneers throughout. Basswood is another type of aviation-grade plywood that is lighter and more flexible than mahogany and birch plywood but has slightly less structural strength. Aviation-grade plywood is manufactured to a number of specifications including those outlined since 1931 in the Germanischer Lloyd Rules for Surveying and Testing of Plywood for Aircraft and MIL-P-607, the latter of which calls for shear testing after immersion in boiling water for three hours to verify the adhesive qualities between the plies and meets specifications.
Decorative plywood (overlaid plywood)
Usually faced with hardwood, including ash, oak, red oak, birch, maple, mahogany, Philippine mahogany (often called lauan, luan or meranti and having no relation to true mahogany), rosewood, teak and a large number of other hardwoods.
Flexible plywood is designed for making curved parts, a practice which dates back to the 1850s in furniture making.
Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in both humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water and Boil Proof (WBP) glue similar to most exterior plywoods.
Marine plywood can be graded as being compliant with BS 1088, which is a British Standard for marine plywood and IS:710 is Bureau of Indian Standards (BIS) for marine grade plywood. There are few international standards for grading marine plywood and most of the standards are voluntary. Some marine plywood has a Lloyd’s of London stamp that certifies it to be BS 1088 compliant. Some plywood is also labeled based on the wood used to manufacture it. Examples of this are Okoumé or Meranti.
How is Plywood Made?
Selecting logs and conditioning
The entire plywood-making process begins with log selection. At this stage, logs both hardwood and softwood are carefully identified and segregated in terms of hardwood species and quality. The primary objective here is to find logs that would produce veneer with acceptable physical and aesthetic characteristics. Some of the more commonly used hardwoods and softwoods in making plywood are ash, maple, mahogany, Douglas fir, and several pine, cedar and spruce varieties.
Once suitable logs are selected, they are then made to go through a conditioning process to assure that good quality veneer is produced during the peeling process. This process usually involves spraying the logs with water.
Transport to the Mill
Logs are transported from the forest concession to the mill to be processed. Transportation comes with its own environmental issues in some instances, as forest areas are cleared to make room for roads and therefore new trees cannot grow.
Cutting and Debarking
The next step in the plywood making process is to measure the conditioned logs for crosscutting. Once the logs have been cut to length, the bark will then be removed using a debarking machine. The debarking process also aims to improve cross-section roundness.
Peeling and clipping
Using a rotary lathe machine, the logs will be peeled into thin veneers. The veneers produced can come in the form of continuous sheets, or immediately clipped into a predetermined width and length.
Since the quality of the veneer is one of the single most important factors in determining plywood grade, veneers with visible defects are clipped off. As a result, clipping leaves some veneers end up with a smaller surface area. This, however, isn’t a problem, because these smaller veneers can be joined together to form standard 4×8 or 3×7 sheets.
Drying the veneer
As you can expect, the green veneers produced by the peeling process are typically wet or full of moisture, and need to be dried. Veneer drying is necessary for improved bonding, and is done by feeding the veneers into continuous or roller dryers at a controlled speed. These dryers produce heat from steam boilers that are fuelled by barks, discarded
veneers, sawdust and other mill residues. Ideally, the moisture content of veneers should only be somewhere between six to 14 per cent by the time they make it through the other end of the dryer.
Composing the sheets
After properly drying and trimming the veneers, they are then composed into final 4×8 sheets. At this stage, they are also segregated as face, core or back veneers. The face is the surface that is to be used or seen. The back, as the term suggests, is the part that remains unused or hidden. The core, meanwhile, refers to the centre layer. The process is meant to make composing the plywood layout easier. The plywood layout, for its part, will be controlled in terms of thickness, timber grain orientation, wood species, and the quality of the ply.
Bonding using adhesives
Once the sheets are properly composed, they are then bonded with the use of adhesives. The adhesives to be used at this point will depend on the type of plywood being produced. If the plywood is meant to be of the general or normal type, urea formaldehyde resins are typically used. Marine plywood, on the other hand, use melamine or phenol-based adhesives.
To make sure that the adhesive is evenly spread on alternate layers of veneer, mills pass the veneers through a mechanical glue spreader. This will then be followed by composed them into panels in odd numbered layers. The thickness of the final plywood product will be determined by the number of veneer layers.
Cold press, then hot press
The composed panels are then pre-pressed in a cold press at an ambient temperature and a controlled hydraulic pressure. This process usually takes 20 minutes, which is enough time for the adhesive to solidify and effectively bond the veneer plys in each panel. Aside from helping with bonding, this process also helps flatten the plywood.
To assure excellent bonding, the pre-pressed panels will then be put into a hot press. This process takes approximately three to seven minutes, although the time—as well as the temperature—may vary depending on the wood species, the veneer thickness and the design of the plywood.
After the pressing process, the panel is ready for quality control. Samples will be randomly picked and tested for mechanical strength, bonding strength as well as formaldehyde emission levels. A visual check will also be performed, and should there be any gaps, they will be filled with putty.
Sanding and trimming
Once the plywood passes quality control, it will then be sanded to make sure the surface has a smooth surface and its thickness uniform. Depending on market specifications, the plywood can either be sanded on the face side or both face and back sides. After sanding, the plywood will then be trimmed to its final size.
Packing, stacking and stamping
Finally, the finished plywood will be packed, stacked and stamped accordingly for shipment to both local and overseas markets. The stamps will usually indicate a grade-
trademark that is meant to inform buyers about the plywood’s exposure rating, grade, mill number, and other factors.
The plywood manufacturing process is quite interesting, isn’t it? Now that your question, “How is plywood made?” has been answered, you now know that a lot of effort is poured into each sheet of plywood. This way, people are assured that they have a high-quality product in their hands which they can use for just about any building project they embark on.
Film faced Plywood
Film faced plywood is lightweight, resistant to corrosion attack and water, easily combined with other materials and easy to clean and cut. Treating the film faced plywood’s edges with waterproof paint makes it highly water-and wear-resistant. Due to its durability and easily handled surface it can be used in open environment in construction and building e.g. warehouses, railway wagons, floors and sidewalls of trucks etc. Coating the film faced plywood with high-quality import films ensures hardness and damage resistance. The surface of the film faced plywood is hygienic and resistant to strong detergents, which is important for farming constructions and storage of food products. It can be used in conditions of high temperature drop, influence of moisture, detergent cleaning and provides protection against termites.
We offer two types of film faced plywood. The first being birch film faced plywood which is very resistant to water, easy to clean and cut and one of the world’s best quality plywood’s.
The second is poplar film faced plywood. This plywood type is also easy to clean and cut and is softer and lighter material than birch film faced plywood.
Field of Application
Due to its durability film faced plywood is widely used in construction and building and vehicle industry for making transport equipment containers, loading platforms, truck and trailer floors and wagons.
This material is also used for making furniture such as chairs, tables, sofas, beds etc. Film faced plywood can also be used to build sliding doors, advertising boards, play ground equipments, floors for sports arenas, smooth concrete casts, scaffolding, hoardings and fencings, packing and in internal & external design and panelling.
Grade : F/F , F/W , W/W ,
Glue type : Phenol-formaldehyde (WBP), Melamine (Urea-melamine-formaldehyde)
Film Weight : 120 g/m² – 400 rotations according to Taber test (EN 438-2)
220 g/m² – 750 rotations according to Taber test (EN 438-2)
Film Color : DBO – Dark Brown Opaque. Different colors and film weights are available on request.
Density : 680 – 700 kg/m³