From exterior wall sheathing to cabinetry, plywood serves countless uses and is one of the most ubiquitous building materials, especially here in the Pacific Northwest. With so many uses and different types of plywood available, it’s important to know your options, understand the material, and pick the right product for your project.
For our Plywood Series, we’re joined by T.R. Cauthorn, Panel Sales Manager at Hampton Lumber, a leading sustainable lumber producer based in Washington and Oregon and one of Dunn Lumber’s long-standing suppliers. With nearly 30 years spent with Hampton Lumber, plus experience working in mills and forests with Georgia Pacific, T.R. is a plywood expert.
In today’s episode, T.R. takes us through the production line to see how a sheet of plywood is manufactured, from log to panel.
Watch our discussion in the video above or keep reading to get the highlights.
Anatomy of a piece of plywood
Plywood is made by pressing and bonding several sheets of wood veneer together. Each layer of veneer alternates the direction of the wood fiber to increase the strength of the panel. Four-ply panels have four layers of veneer, five-ply panels have five, and so on. The veneers on the outside of the stack are called the face and back, while the inner layers are called the “core and center.”
Step 1: Peeling and drying of veneer
First, logs are run through a “de-barker” to remove the bark, then cut into equal segments and sent through a heat vat or steam tunnel. The heating process makes the wood pliable to ensure a smooth, clean clean peel when it reaches the lathe, where it’s processed into a thin “ribbon” and clipped to usable core and full sheet sizes. The veneer is then put through a dryer, and after the drying process it is separated by grade. Once the dry veneers have been graded, they are ready for the lay-up process.
Step 2: Gluing and lay-up
The next step in the manufacturing process is gluing the veneers together. To make an industrial use panel, siding/sanded or a seven-ply, mills will often utilize the spreader crew. Most plywood mills also incorporate a lay-up line in their manufacturing process. The layup line focuses on three-, four- and five-ply panels due to its limited number of stations.
The spreader crew requires at least four people: one person runs the veneers into a glue machine, while the others retrieve and stack each layer manually. A layup line is a mostly automated pressing process, wherein veneers travel down a conveyer line, are sprayed with glue, and are stacked on top of each other. The spreader crew is utilized for 4x8, 4x9, and 4x10 T-111 siding, sanded and industrial panels, as well as all seven- or nine-ply panels. The layup line is typically where you will see more higher volume items such as wall and roof sheathing.
Step 3: Pressing and finishing
Following the gluing process, sheets are pressed together in a two-step process. The first step is a “cold” press, meaning only weight is applied. This step helps to jump-start the bonding process and ensure each sheet holds together through the second press. It’s essential to get the duration of the cold press right—if the sheets spend too long in this step, the glue will dry out causing the veneers to delaminate. The second press—the "hot" press—seals the bond by exposing the sheet to high heat for about 10 minutes.
Once the sheets have cooled following the hot press, they’re ready for finishing. Each sheet is routed through saws for finished edges. Plywood products that are sold for sheathing are complete at this point, while sanded plywood will go through one additional sanding step before they’re ready for distribution.
Step 4: Sanding and Patching
You’ll often see plywood products with football-shaped cut-outs on the surface; these patches are made after the veneers are dried and before the lay-up process starts. Plywood mills will always upgrade their veneers or panels through the patching process, with the goal of moving a “B” grade to an “A”, “C” grade to a “B” and so on.
The football-shaped patch is made by a specific type of machine (called a Raymond), which replaces oblong knots or other imperfections with a clean patch. After lay-up, smaller defects like cracks and seams will be filled with either a putty or an epoxy, manually applied with a putty knife or an epoxy gun.
Once through the putty/epoxy line, the plywood is ready to go to the sander. Sanded products like AC, Underlayment and CCPTS go through the sanding line. At the end of the sanding line, the final grading of the panel takes place.
Engineered wood products like plywood are crucial to making better lumber products that promote sustainable harvest practices. If you’re using plywood on your next job, be sure to check out Mike Dunn’s tips for buying plywood. To learn more about other types of engineered lumber, watch our overview of engineered lumber products and how they’re used, and read up on what to know about ApplePly®, a high-end plywood product.