A COMPLETE GUIDE
Plywood is an assembly of wood veneers (Thin layers of wood peeled from trunk logs) bonded together using resin(glue) to produce a flat sheet which is dimensionally and structurally stronger than solid wood. An extremely versatile product, plywood has its usage in a wide range of structural, interior and exterior applications – from form-work through to internal paneling. While plywood can be tailored/manufactured to suit an extensive range of applications, a normal ply panel consists of at least 3 plies and can extend upto 15 plies or more, with the wood grain in alternate plies running at right angles to each other.
Plywood can be sub-divided into four groups, depending upon specific applications :
• Structural (BWP | IS 10701)
• Exterior (BWR/BWP)
• Interior (MR | IS 303)
• Marine. (BWP | IS 710)
In the following section, we talk about the construction of plywood, how its made, its various grades, their applications and the various benefits of using plywood as a building material.
BENEFITS OF PLYWOOD
1. Increased stability
Additional to all the inherent advantages of the parent wood, plywood exhibits enhanced properties in its laminated structure.
2.High impact resistance
Plywood being a wood based panel, has the ability to tolerate temporary short-term overloads; up to twice the design load. This is specifically useful wherever there are chances of seismic activity or cyclonic winds. Plywood is also extensively used as construction flooring or as concrete formwork. Plywood’s laminated structure is designed to distribute loads from impact over a larger area on the opposite face, which effectively reduces the overall tensile stress.
3. Surface dimensional stability
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4. High strength to weight ratio
Owing to its cross laminated construction, Plywood also exhibits a high strength to weight ratio making it very cost effective to use plywood in structural applications such as flooring, shearwalls, formwork and webbed beams.
5. Panel shear
Plywood exhibits high Panel shear strength, nearly double that of solid timber, due its cross laminated structure again. This allows plywood to be highly effective when used in gussets for portal frames, webs of fabricated beams and as bracing panels.
6. Chemical resistance
Since most of the manufactured plywood panels are treated chemically, Plywood does not corrode and can be used in chemical works and cooling towers as a cost-effective, durable material.
1. Increased stability
Additional to all the inherent advantages of the parent wood, plywood exhibits enhanced properties in its laminated structure.
2.High impact resistance
Plywood being a wood based panel, has the ability to tolerate temporary short-term overloads; up to twice the design load. This is specifically useful wherever there are chances of seismic activity or cyclonic winds. Plywood is also extensively used as construction flooring or as concrete formwork. Plywood’s laminated structure is designed to distribute loads from impact over a larger area on the opposite face, which effectively reduces the overall tensile stress.
3. Surface dimensional stability
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4. High strength to weight ratio
Owing to its cross laminated construction, Plywood also exhibits a high strength to weight ratio making it very cost effective to use plywood in structural applications such as flooring, shearwalls, formwork and webbed beams.
5. Panel shear
Plywood exhibits high Panel shear strength, nearly double that of solid timber, due its cross laminated structure again. This allows plywood to be highly effective when used in gussets for portal frames, webs of fabricated beams and as bracing panels.
6. Chemical resistance
Since most of the manufactured plywood panels are treated chemically, Plywood does not corrode and can be used in chemical works and cooling towers as a cost-effective, durable material.
SUSTAINABILITY
What makes building with plywood sustainable ?
DURABILITY
The durability of plywood depends majorly on the bonding quality used in manufacturing which depends on the resin (glue) used while stacking up wood veneers on top of each other. Plywood in general is manufactured using two primary adhesives. The exterior grade marine ply is manufactured using a phenolic based formaldehyde resin while the interior grades are generally manufactured with Melamine fortified Urea formaldehyde resin. Structural plywood is manufactured from a variety of hardwood and softwood species, which may not be durable in exposed weather situations, and therefore must be preservative treated to ensure its full service life can be reached.
SIZES
GRADES & THEIR APPLICATIONS
Interior plywood – These are plywood used in non-structural interior applications which are generally not subject to high load, but where an aesthetic finish is priority. Its applications include furniture construction such as cabinets, tables, shelves, internal wall paneling, furniture, ceiling linings and interior door skins. Interior Grade of plywood is generally referred to as MR Grade or Commercial Grade in the Indian Market Space. It meets the specifications of IS – 303.
Exterior plywood – Exterior grade of plywood is intended for use in exterior applications subject to the elements occasionally, where a high quality aesthetic finish is also required. Exterior Grade plywood in India generally refers to Marine Ply. Applications include outdoor furniture, flooring, exterior door skins, hoarding, signs and non-structural cladding.
Marine plywood – Marine Ply is a subset of Exterior grade plywood. Its a structural plywood intended for hulls of boats and yachts and other furniture applications such as in washrooms, kitchens or outside furniture meant to withstand the elements specifically water. It is also used in aircraft construction. Marine plywood is manufactured to minimize water penetration, and uses Phenolic bonded formaldehyde adhesive bond.
TREATMENTS OF PLYWOOD
For residential or commercial construction purposes, the most suitable treatments are Copper Chromium Arsenate (CCA) and Light Organic Solvent Preservative (LOSP).
HANDLING & STORAGE OF PLYWOOD DONE RIGHT
COMMON ISSUES IN PLYWOOD
Thickness Variation – When plywood is made, the alternating layers of core veneers are glued together with heat and pressure. During this process, there is some degree of compression in the core layers. Different parts of a layer may compress more than others, and each layer will pick up inconsistencies from adjacent layers and this compression is largely unpredictable. The rules are written such that hardwood plywood cannot be thicker than its nominal size, but it can be up to 0.5 – 1mm thinner. The reasoning is that a below thickness panel will still fit in a groove cut at the nominal size, but an over thick panel would not.
Bending or Warping – It is a common occurrence in plywood panels for it to warp or bend due to differences in humidity/moisture and temperature. We explain why it does so and how to tackle it if it does.
Splitting – Splitting generally is referred to split in the layers of plies in the plywood panel when being cut or when a nail or screw is being driven in the edge of a panel. This is largely a construction error where the layers may have failed to bond properly while pressing or if there were too many overlappings or voids during the construction/composition of the multiple layers of a plywood panel. On an average for Indian factories, Splitting problem should not exceed 2% of the total sheet production. Ask for replacement if you stumble across this issue.
We list here a number of quality checks that can be performed while purchasing plywood to ensure you buy genuine and good quality plywood. Click here.