There’s no question about it: Plywood pricing and grading can be confusing. The core matters, when it comes to finding quality plywood. It’s not just the materials that comprise the core, but the number of plies and quality of glue that makes a difference. Let’s read between the layers and take a look at what’s between the plies of plywood.
Glue Quality Considerations
Essentially, a sheet of plywood is made up of multiple layers, or plies, plus the glue that holds them together. Some people theorize that the more plies, the better, because more plies means that the veneers are cut more thinly, producing less movement. However, more plies translates into more glue, so if the glue is the high-quality variety, then yes, more plies might actually mean greater stability. But what if the glue is an inferior product or is ineffectively applied? In those situations, more glue will just mean more inferior product is included in the plywood, making it inferior as well. Whether the glue is holding 6 or 12 plies together, if it’s not the good stuff, the plywood won’t hold up the greatest. Not only is the actual product used important, but the quality control in the glue-application process comes into play, as well.
Glue Cost Realities
Approximately 1/3 the cost of any sheet of plywood is due to the glue. Unlike the cost of wood, that cost is fairly constant — constantly expensive, that is. Depending on the grade and species of wood used in the plywood, the lumber market may mean that the price fluctuates quite a bit; however, the price for plywood won’t fluctuate nearly as much as solid wood of the same species.
However, when plywood manufacturers realize that the same volume of glue can be stretched out to make 10 or 20 more panels, the savings for them will be apparent. Unfortunately, so will the stability of the resulting panels.
Glue Application Issues
Sometimes people think they’ll avoid issues relating to glue by asking about the type and formula of glue being used, but that information really won’t tell the whole story about the quality of the panel. Really, there isn’t much variety when it comes to glue formulations; the issue is usually not about the glue itself but about its application. The typical foreign mill will make use of extenders to essentially water down the glue to increase its coverage. Modern automation allows those mills to be able to make thinner glue lines, further extending the glue. Sometimes automated plants can even run the risk of the glue vat drying up completely while the line is running. As you can imagine, one potential result is delaminated panels with little or no glue between the plies that were able to be held temporarily together merely by heat pressure combined with a little glue residue which was left on the rollers.
Hopefully you now understand why not the glue itself, but the consistency and quality control used in the manufacturing process is really where you need to start looking. How, exactly, do you go about that? We’re glad you asked. Check out the sequel to this post to find out more.