Bad smelling chemicals are hard-working chemicals, right?
Well, we used to think that. My grandmother used to take my Mom to walk over the Bayonne Bridge in New Jersey when she had whooping cough as a child, because Gram thought the chemical fumes from the processing plants under the bridge cleared her lungs.
Not such a great idea, we’ve come to learn. Indeed, our understanding of fumes has come a long way since the 1940s.
The reason some adhesives are so fumy and smell so poisonous is that the solvents used to convey the adhesive chemicals to the contact point (e.g. the wood joint) are evaporating…and wafting into your nose where it gets into your lungs, liver, and kidneys.
The evaporation of solvents that you smell at room temperature doesn’t happen when the glue is heated, nor when it is cooled. It happens at room temperature, as soon as the lid is taken off the can or the glue starts to ooze from its container.
That’s important to understand because when something evaporates at room temperature – e.g. gasoline, nail polish remover, high-gloss polyurethane – it’s called volatile. When a solvent that’s evaporating at room temperature is a carbon-based compound, which is highly likely, then the evaporating solvent is called a volatile organic compound, or VOC.
The problem with VOCs (whether they are used as solvents in glue or sealants or paint) is that VOCs react with sunlight to cause smog. More importantly, VOCs are very unhealthy to breathe, especially for people with asthma or respiratory problems. Plus, they are poisonous to the environment to refine and manufacture, including such nasty chemicals as naphtha, toluene, xylene, and benzene…all hydrocarbons.
So, what can we use to replace VOCs as a solvent in glues? For starters, you’d need a universal solvent that can dissolve (or react with) the adhesive chemicals, yet the solvent would have to evaporate rather quickly.
How about water?
Yup. That’s it. In so-called green adhesive, water is now being used to replace VOCs, as well as in many other building products that depended on volatile organic compounds in the past.
Water evaporates harmlessly, and it’s a great solvent, as long as the chemicals it is meant to dissolve are engineered to be water-soluble.
The only problem with water-based solvents in woodworking is that water swells the wood, pretty much on contact. So woodworkers and craftsmen are typically not sloshing in water-based adhesives to seal up their wood joints, if swelling is going to be a problem. (There are cases when it is not a real problem, as in framing and subfloor decking.) Accordingly, there is a whole range of either low-VOC adhesives available (as certified by the EPA) or adhesives that react with ambient moisture, yet don’t introduce meaningful amounts of water to the surface of the wood. These include very popular adhesives like cyanoacrylates, under brand names like The Original Super Glue®, Krazy Glue®, or Gorilla® Super Glue. These adhesives are not water-intensive, which is great for woodworking. They are acrylic resins that “polymerize” (form long bonding chains) in the presence of moisture, which is provided by the ambient humidity. Other products that are effective adhesives (yet do not release VOCs) include polyurethane glues, like the original Gorilla® Glue and many other brands in this class. After that, choices start getting sticky, if you will excuse the pun, because you get into the range of formaldehyde products, like phenol formaldehyde resin, resorcinol-formaldehyde resin, and urea-formaldehyde. They may perform beautifully, but formaldehyde is known carcinogen, and we should all be staying away from that.
Want to go green when gluing up?
Use water-based adhesive.
Want to avoid water but you still need the good bond?
Go with cyanoacrylates and urethanes…but stay away from the formaldehyde, now and forever.