Outdoor gluing know-how
Got something outdoors that needs gluing? Over the last couple of decades, excellent exterior grade glues have become available. They’re easy to use, widely sold and entirely effective. Until these advances happened, it was difficult to glue outdoor items reliably. These days one evolutionary change in a particular type of glue has made a big difference.
One of the oldest types of glues around is generically called polyvinyl acetate (PVA). Traditional white, yellow and brown wood glues fall into this category. They’re excellent for gluing dry wood that won’t ever get wet, but water was always their downfall. There was never any problem with short-term exposure to water, but the original formulations of PVA all turned to mush after extended contact with moisture. Slowly, stepby-step, glue manufacturers began enhancing the water resistance of PVA glues with a chemical modification called cross linking. At first, this only increased the water resistance, but today it’s considerably better. The best cross linking PVA glues are now consider completely waterproof. They still come out of a bottle, they still clean up nicely with water when wet, they have no smell, but after they’re fully dry water doesn’t have an effect any more. The best and most widely available waterproof PVA glue is called Titebond III. It works well for interior applications but also for outdoor situations involving porous materials such as wood. For gluing non-porous materials outdoors there are two options that work better than cross linking PVA, and chances are you’ve never used either of them.
In the world of glue, there’s something called construction adhesives. These thick, non-flowing products come in caulking tubes and are made mostly for gluing wood during house construction. And I have to say that I’ve been almost universally disappointed with construction adhesives in the past because they’re so weak. The only exception to this is something called PL Premium. It’s sold in caulking tubes on store shelves right next to all those sub-standard construction adhesives but it’s entirely different. PL Premium is a very strong adhesive that dries hard and it’s useful for gluing all kinds of things, including wood and non-porous materials. One of the reasons it works so well is that it’s made with polyurethane chemistry. This means it doesn’t mind wet conditions at all. In fact, a little moisture actually makes it harden better and faster. There’s no better option than PL Premium for securing, say, a subfloor during house construction, but I also keep tubes on hand for all kinds of outdoor work. I’ve never had this stuff let me down, except for one drawback. PL Premium is thick in texture – thicker in consistency than toothpaste – which is not always what you want for finer work. In cases like these, another type of polyurethane adhesive works very well.
If you go to the hardware store you’ll find a family of liquid glues called polyurethane, but it’s different than PL Premium. Liquid polyurethane glues are transparent golden brown in colour and they’re exceptionally good at bonding non-porous materials, both in dry and wet situations. As with PL Premium, polyurethane glues need a bit of moisture to cure. I’ve also never found any difference in quality from one brand to the next. Gorilla Glue was the first brand of liquid polyurethane glue to become popular, but now all manufacturers offer their own versions. I like polyurethane glue, but there are two warnings you need to know about. First, this stuff does not clean up easily. Acetone is the only option I’ve found that cleans it up, and only then when it’s still liquid. Also, liquid polyurethane expands as it cures, leaving behind a hardened kind of foam. Don’t use too much!