Let’s Get Physical
Every now and again we as decorative plywood manufacturers (Columbia Forest Products) are asked to provide values for various physical properties of our products, ostensibly for purposes of comparing such values with those of other building materials in order to ensure suitability of a given panel for a given application. While on the surface this sounds like a reasonable request, many times it is met with hesitation and uncertainty.
So, why is that?
The American National Standard for Particleboard, ANSI A208.1-2009 and the American National Standard for Medium Density Fiberboard (MDF) for Interior Applications, ANSI A 208.2-2009 both contain tables listing minimum mechanical property requirements for the respective products they cover, to include:
- Modulus of Elasticity (MOE): the ratio of stress to strain within the elastic range of a given material
- Modulus of Rupture (MOR): the stress of bending sustained at the point of failure (rupture)
- Internal Bond (IB): the amount of force required to cause an artificially induced bond between wood fibers to fail under controlled conditions
- Screw-Holding, or Screw Withdrawal Resistance: force required to cause a failure of a given size wood screw inserted to a prescribed depth into a given specimen
- Thickness Swell: percentage of increase in thickness caused by exposure to water
- Linear Expansion: measure of shrinkage or swelling potential in an engineered wood product due to moisture loss or gain in service
Because particleboard and MDF are used for such a wide variety of applications, many of which may be structural in nature, and because these products have predictable and reproducible properties in all directions, these values may relate to performance requirements in certain instances. Hardwood plywood, on the other hand, is produced as an aesthetic rather than a structural product. Thus, the standards to which they are manufactured, either theAmerican National Standard for Hardwood and Decorative Plywood, ANSI/HPVA HP-1-2004, or the AWI Architectural Woodwork Standards, both of which establish minimum criteria that relate more to the potential uses of hardwood plywood in serviceability and aesthetic rather than structural applications, do not include requirements for mechanical properties.
The Engineered Wood Association (formerly the APA), which represents manufacturers of structural plywood, often referred to as “softwood plywood,” does not include references to MOR, MOE, or IB in their US Product Standard PS-1-07, as they consider that APA structural panels are manufactured to different standards for attributes that more closely relate to performance expectations during their intended use in structural applications. They do, however, publish a separate, non-standard related technical paper that doesinclude those properties for comparative purposes. Many manufacturers of decorative plywood have collected at least some physical properties data from testing done over the years, but because this information is so infrequently sought, and because it isn’t generally published as public information or for architectural use like that of APA, the person receiving the inquiry may not be familiar with the information’s whereabouts. And then, it really starts to get complicated…
Photo courtesy of Instron Materials Testing Solutions. www.instron.us
The Burger King® connection
According to more than one source, there are 221,184 ways to order a Burger King Whopper “your way.” While I find this a staggering if not dubious number, I am sure that when you think of all the things that you could ask for on that famous hamburger, there must be a lot of different combinations, even if it doesn’t total 221,184. To the extent that hardwood and decorative plywood is a “have it your way” product, it is a little like Burger King, except the number of potential combinations may dwarf the aforementioned 221,184.
When you consider that our industry produces decorative panels with veneer core, combination veneer and engineered core, lumber core, MDF core, and particleboard core, to name just the major core types, in thicknesses from 1/8″ to 1 ½” or thicker, the numbers start to get high.
Add to that the half dozen or more softwood core species such as but not limited to the spruces (Picea spp.), true firs (Abies spp.), Douglas fir (Pseudotsuga menziesii), the numerous white and yellow pines (Pinus spp.), the domestic hardwood core species to include but not limited to the aspens and cottonwoods or true poplars (Populus spp.), yellow or tulip poplar (Liriodendron tulipifera), basswood (Tilia spp.), sweetgum (Liquidambar styraciflua), birch (Betula spp.), the imported species to include but not limited to the lauans (Shorea spp. and related), lupuna (Chorisia spp), sande (Brosimum utile), ceiba/sumauma/fuma (Ceiba pentandra), breu/almaciga (Protium spp.), okoume (Aucoumea klaineana), obeche/ayous (Triplochiton scleroxylon), in addition to just the 150 face species listed in the Veneer Species Guide published by the Hardwood Plywood and Veneer Association, in up to 6 face grades and 4 back grades for each possible combination, I think we got BK beat, don’t you?
We must also consider that while engineered cores like MDF and particleboard have similar properties in all directions, solid wood is anisotropic in nature, meaning it has different properties along its width, length, and thickness. This means a veneer core panel using layers of wood veneers laid up with the grain direction of adjacent plies alternating at parallel to and perpendicular to that of the face, while somewhat neutralizing those differences, will not eliminate them, giving even more variation to each construction.
All that considered, a table showing physical and mechanical properties for every possible configuration would be hieroglyphic in appearance. Additionally, we are as you might expect, reticent about publishing exact test results because of the nature of the product. Since no two tests even on similarly constructed products would ever produce exact duplicative values, there are concerns that such values could be improperly interpreted to be guaranteed values, and this just cannot be the case.
But there must be some numbers we can use!
Ok…here goes. The following chart includes numbers published in ANSI A 208.1-2009 for Particleboard, ANSI A 208.2-2009 for MDF, the American Plywood Association’s Technical Topics, Mechanical Properties of APA Structural Panels (not a standard), and a collection of values accumulated over several years for a wild assortment of hardwood and decorative plywood, again, not to any standard.
Before we go…
As expected, the numbers for veneer core hardwood plywood are all over the board due to the many considerations enumerated above. Please understand that these are very, VERY, general in nature and not intended to represent any specific value for any specific product you may choose for any application. Hopefully, however, you will find them useful for comparative purposes! Burger King, anyone?