Plywood Strengths

I was wondering why almost every plane on the forum has used Birch plywood and not Mahogany. Infestation with termites is usually not a problem for plywood when used in above ground applications. If the plywood has more than seven layers, it is the strongest and can be used for special projects such as guitar bodies or router patterns. This 1-inch-thick fir plywood is also available with tongue and groove patterns that lock together for even more strength.

Plywood is used in many applications that need high-quality, high-strength sheet material. The mechanical and physical properties of plywood are dependent upon the particular construction employed. Plywood is available in practically any size, but the 1.2 x 2.4 m panel has become the standard production unit of the industry. Plywood has certain intrinsic qualities that add much to any structure or construction in which it is used.

The oak and birch plywood the big home-improvement stores had in stock (about $40) at the time of writing this was graded C3. The difference in price is mostly in the difference in the veneer. Before finishing, ensure the plywood is dry (below 12 – 15% moisture content) and the surface to be painted is clean, smooth and wax free. Many woodworkers object on principle to using anything but veneer-core plywood.

Citation needed The American designers Charles and Ray Eames are known for their plywood-based furniture, as is Finnish Architect Alvar Aalto and his firm Artek , while Phil Bolger has designed a wide range of boats built primarily of plywood. Sizes on specialised plywood for concrete-forming can range from 6 to 21 mm (0.24 to 0.83 in), and a multitude of formats exist, though 15×750×1,500 mm (0.59 inch × 2.46×4.92 ft) is very commonly used. Advice should be sought from the plywood manufacturer or the Engineered Wood Products Association of Australasia (EWPAA), as to the permitted location and size of holes.

The core material is specified separately from the face, so you can have maple plywood with a veneer core (which is similar to construction-type plywood) or with a particle- board or medium-density fiberboard core. You also need to look at the strength per unit weight, not the strength per dimension unit measure. Plywood or wood treated in this manner will not support combustion but will char when heated beyond the normal charring point of the wood. This plywood, like all structural plywood made until the mid 1930’s, was bonded with non-waterproof blood and soybean glue. The usual purpose of plywood now is not aesthetic but to obtain high strength with low weight.

The type of adhesive used to bond the layers of wood together depends on the specific application for the finished plywood. Fire-resistant plywood is manufactured by impregnating the core stock with a salt solution, which, upon evaporation, leaves a salt deposit in the wood. The Plywood Association of Australia (PAA) grading standards are as specified in the following table. Poorly manufactured plywood also has a tendency to split or delaminate, especially when nails or screws are driven into the edges.

The number of plywood constructions is almost endless when one considers the number of wood species available, the many thicknesses of wood veneers used in the outer plies or cores, the placement of the adjacent plies, the types of adhesives and their qualities, various manufacturing processes, and more technical variations. And wood scientists agree that the structural performance of osb and plywood are equivalent.

This makes plywood a highly effective material to use in gussets for portal frames, webs of fabricated beams and as bracing panels. Veneer quality, glue type and timber species are the major contributing factors that determine the application of a plywood panel. In most cases, only about 50-75% of the usable volume of wood in a tree is converted into plywood. Basswood is another type of aviation-grade plywood that is lighter and more flexible than mahogany and birch plywood but has slightly less citation needed structural strength.

In his patent applications, he described the concept of laminating several layers of veneer with glue to form a thicker piece – the first description of what we now call plywood. Particleboard core or MDF (medium density fiberboard) core are the other common types of plywood cores in use. Just some background – OSB and Plywood are measured on strength and not thickness and that is what determines the span rating.


Plywood is often used to create curved surfaces because it can easily bend with the grain. The only way I know to check plywood for a concentrated load on a span of plywood would be to get the APA specification and use basic statics, analysis, etc. Generally speaking, pressure treated plywood may be acceptable for house projects but not for boats. As we look at how plywood is made, and the material it’s made from, we begin to understand why.

It is not as stiff as plywood and can sag with if too much weight is applied to it. For example, when MDF is used for shelving, it is important to reinforce the shelves to prevent sagging. On the other hand, subzero conditions don’t affect plywood’s dimensional or strength properties, which makes some special applications possible. Plywood is also used as an engineering material for stressed-skin applications.

Pressure treating of the manufactured plywood – pressure treating plywood is an ‘envelope treatment’ only, treating the outer veneers, edges and ends of sheet. Plywood is an outgrowth of the laminated wood known as veneer, which consists of an outside sheet of hardwood glued to a base of lower-cost wood. Plywood (structural) can be utilised very effectively as bracing, webs as well as gussets in portal frame construction. Plywood is an assemblage of wood veneers bonded together to produce a flat sheet.

Nonimpregnated plywood can be made fire resistant by applying surface coatings such as intumescent paint and chemicals such as borax. Today, plywood has replaced cut lumber for many construction purposes, and plywood manufacturing has become a multi-billion dollar, worldwide industry. Some plywood from South America and Asia is graded on a similar system, but much of this material is not graded. When you laminate a hull, as in cold-molded construction, you are actually making plywood to a specific shape, that of a boat hull (see Laminated construction gives lasting value ).

Softwood plywood sheets designed for installation on the exterior of a structure usually use a phenol-formaldehyde resin as an adhesive because of its excellent strength and resistance to moisture. Most softwood plywood is composed of Douglas fir, but western hemlock, white fir, ponderosa pine, redwood, and other wood species are also used. The sheets of veneer obtained from this process are cut to the desired dimensions, dried, patched, glued together, and then baked in a press at 140 °C (284 °F) and 1.9 MPa (280 psi) to form a plywood panel. Before a frame structure has plywood nailed to it, it is very fragile and can be knocked down easily by a strong wind.

Most plywood panels are overbuilt to cover the statistical range that guarantees each sheet of plywood meets the minimum standard. Though plywood is more water resistant than MDF, it is still porous and susceptible to damage when exposed to water over time. Whenever plywood is employed in a structure, fewer and smaller fastenings can be specified because consideration need be given only to the holding power of the fastener and the tensile strength of the fastening itself.

In practical applications of wood products, the increase in strength due to exposure to subnormal temperature will tend to offset strength losses caused by other factors. Depending on the grade of plywood , it may or may not be smooth and useful for visually pleasing interior wood pieces. As over 70% of the PAA plywood sold is of an exterior type we shall examine in detail the different varieties available and their characteristics and uses. Such plywood is called overlaid plywood and is commonly used in the construction, transportation, and agricultural industries.

MDF weighs a ton,and the dust is horrible,you get dirty when you work it.Plywood is a lot lighter,cleaner,and smells better,and holds screws,nails,dowels,better.Plywood would repair has it uses but for cabinets i would choose plywood,cost wise it isn`t that much more. Fasteners driven in the edges of plywood can cause an inferior core to split, often delaminating adjacent layers.

Hardwood plywood is considered to be an appearance product, as opposed to softwood plywood, which is considered a structural material. There really ISN’T that much strength needed for a rib filler (web) and glue area starts to define the design. N.B. special types of structural plywood can be manufactured using A, B or S quality faces to order. Expect to pay $75 or more for a 4′ x 8′ sheet of A2 plywood with plain-sliced veneer.

First of all compare apples to apples – ie MDF is not comperable to plywood because they are different products entirely, as I’m sure you know. In exposed applications, structural plywood must be preservative treated to ensure it lasts its full service life and surface finished to minimise surface checking. Normally, changes in area due to changing load and necking are disregarded in determining ultimate strength. Plywood is given special consideration whenever lightness and strength are desired. The durability of plywood will in part depend on the bond quality used in manufacturing. Today, southern pine plywood accounts for about half of all structural plywood sold.

It should be noted that although the F-Grade characteristic strength and stiffness values of structural plywood and structural timber are the same for bending, tension, compression and modulus of elasticity; shear capacity of structural plywood is superior and Modulus of Rigidity is marginally reduced. C. For composite and four-ply plywood structural panel, load shall be reduced by 15 pounds per square foot. Osb and plywood share the same exposure durability classifications: Interior, Exposure 1 (95% of all structural panels), Exposure 2 and Exterior.