Blog: The Truth About Laminated Wood By: John Heisz
In the comments on my build video for the doors I’m making for my house, a number of people questioned the use of plywood as the main building material:
“How did you stop the warping of the plywood?”
“Just wondering how do you go with any twisting/curving of the plywood over time? I have heard that plywood will do that. Or with the way you have constructed the door that isn’t an issue?”
A valid question, since the plywood I used is not known for staying perfectly flat. Even worse are the lower grades of sheathing plywood sold at every lumber yard. But there is a way to control or completely eliminate the warping and twisting, and that’s to laminate pieces together.
Of course, it only works if what you are building is thicker than the plywood itself, like a 1-1/2″ thick door made from layers of 1/2″ plywood. The magic happens when you build up the layers with a strong glue and then clamp it to a form while the glue dries. In my plywood door example, I have the straight and flat top of my workbench to clamp it down to. After the glue sets, the resulting lamination will hold that shape and stay flat. And that’s even if the plywood pieces themselves were not flat before the glue up.
Now I should say that while this method is very effective, it’s not completely foolproof. There are things that you can do to make it more likely to succeed, like being selective with the materials you use. The flatter the parts are before the glue up, the better the chance that the lamination with stay flat. Positioning the parts so that any existing bend is offset by the next piece bending the opposite way will improve the chances of a perfectly flat result. Also, adding more structure will help – I used solid wood for the edge of the door and the made a big difference.
This method can also be used for things that are not flat. You can basically create any shape you want, be it curved or twisted, using this method. I’ve used it several times in the past for furniture projects and a recent example is my all wood C clamp that is made from a lamination:
All but impossible to do with solid wood. And stronger, and that brings up the next major advantage of laminating wood – the resulting member is usually stronger than the same size solid wood piece. I’m not 100% clear on the engineering or physics of it, but it has to do with the glue bond between the layers, especially when that bond is stronger the the wood itself.
And it’s a strength that can be calculated and relied upon to be consistent, even when you use wood that varies in quality for the layers. A great example of this is laminated veneer lumber for construction, or LVL. These are multiple layers of thin sheets of solid wood glued together to make a plank. Even though it looks like plywood, all of the grain goes in the same direction. These are not only tremendously stronger, they also resist the warping, cupping and cracking that plagues traditional construction lumber.
As with everything else, there are some disadvantages to using laminated wood. First is that it is labour intensive to make. From the cutting of the strips to the building of the form to the assembly it can take a considerable amount of time. There is also the added cost associated with using a large amount of glue. And the glue must be strong enough. Strength is not a problem for regular PVA wood glue, but it may not be suitable because of its shorter open time – you need more time to assemble several layers before clamping, and the glue needs to stay liquid long enough for that to happen.
Then there is the problem of delaminating. That can happen if the glue joints fail or if the wood is exposed to excessive moisture. Even if you use waterproof glue, the wood itself is not waterproof and that can cause the bond to break over time.
I talk about this while working on one of the plywood doors I made in this video: