There are a lot of different types of plywood glue. Many formulations have been put together to address specific use cases. But in general there are 3 main type:
- Urea Formaldehyde (including new Soy Based variants)
For interior panels Urea Formaldehyde is the standard and the Soy based glues are now common as a solution to reduce Formaldehyde emissions to be TSCA VI compliant.
In exterior panels Melamine and Phenolic glues are used for their greater bond in wet conditions and ability to withstand higher temperature swings. On the far extreme are the WBP (Water Boil Proof) glues that literally can be dunked in boiling water for hours and hours without failing. These are still Phenolic and Melamine glues but has slightly different formulations.
Plywood Glue and Manufacturing
As with every part of this plywood series, the glue and how it is applied during manufacture will change the quality of the panel and the eventual price of the panel. Changing the glue type, density, and application method will dramatically change how a panel performs and what it costs.
Glue is applied using rollers, curtains, and by spray. The preferred method is by spray as there is much more control over the process. Cheaper is rolling but can be difficult to maintain consistency. Here again one can see how these variables can play a major role in the quality of a panel or as a method to change the cost of a panel.
Use of glue extenders and fillers also play a factor in manufacturing overhead and should not be ignored. But like with any of the elements discussed in this plywood series, changing how much filler is used in glue or how fast the glue is applied isn't necessarily a bad thing. These are variables that can be tweaked to increase production time or reduce the cost of a panel. In the end whether or not it is a good thing depends entirely on what is important to you and your specific use case.
First thanks to everyone who send in plywood questions. I'm still getting them as I write this so obviously I couldn't answer them all. Feel free to ask in the comments below or even keep submitting them through the form on this site and I will add them into shows going forward. Here are the ones I covered in this episode:
- When to use plywood vs solid wood
- What is the application for lumbercore plywood
- Cherry Plywood face veneer quality
- Why is plywood sized in 4x8 sheets?
- Can Plywood factory edges be trusted?
- Foam core plywood for doors?
- How should you join plywood?
- Good panels for laser cutting?
- Where does the sawdust for MDF come from?
- Why are plywood patches always football shaped?
I highly recommend that you pick up a copy of the Hardwood Plywood Handbook put out by HPVA which will detail all of the manufacturing details I have discussed throughout this series and give you some great visuals about face veneer layout and core construction.