They are polymeric compounds that are very similar to epoxy resins. They were discovered by the German chemist Dr. Otto Bayer in 1937. They are usually found as foams, like the insulation foam used in mattresses and the molded foam used in surfboards. They have also been used as adhesives across much of the world since the 1950s.
In the same way that cyanoacrylates need to be mixed with water to harden, polyurethane adhesives need to be mixed with water to harden.
Jordan Smith, a builder and instructor, says that “if you’re gluing concrete to wood, that’s fine.” A: “Concrete has water; wood has water.” A little extra water is needed when one of the materials is not porous. Keep one side of your joint wet with a little spray bottle, then apply glue to the other side and stick them together tight. There are a lot of things you can use to spread polyurethane on big things like wall panels, like trowels.
In this article
- When to Use Polyurethane Glue
- 4 Tips for Using Polyurethane Glue
When to Use Polyurethane Glue
There are many good and bad things about using polyurethane as a glue. First, you need to know what it has and doesn’t have over wood glue and other glues, as well as other options, like epoxy.
Advantages of polyurethane adhesives
Compatibility. Polyurethane adhesives are truly multi-purpose products and can be used to bond a variety of building materials: wood, glass, concrete, metals, carpets, and more. If you are bonding two nonporous materials—like metal on metal—just make sure to moisten the surfaces before you glue them.
Waterproof. Polyurethane bonds are waterproof, which makes them a good choice for projects outside. Though they won’t be able to stay underwater for a long time.
Paintable. Polyurethane, on the other hand, can be painted after it has set. This is different from ordinary adhesives, which will not work well if they are painted.
Set time. When you use polyurethane, you don’t need to clamp it down. As a general rule, polyurethane takes less time to harden than epoxy.
Disadvantages of polyurethane adhesives
Strength. There are a lot of different types of polyurethane construction adhesives out there, with different strengths. If you use a polyurethane instead of epoxy or PVA, you’ll want to make sure it’s strong enough. Yellow glue is one example.
Durability. It can be hard for polyurethanes to keep water out, which makes some of these bonds less strong. As time goes on, polyurethane formulas and other agents have made these bonds more durable.
Short shelf life. This is because polyurethane will start to harden when it gets wet, and this will make it more durable. It has a one-year shelf life.
Toxicity. Polyurethane has known carcinogens, so you’ll want to make sure there is enough ventilation when you apply any polyurethane products, like adhesive. You’ll also want to wear gloves and keep your skin away from it.
Variable set times. Because polyurethane needs moisture to cure and set, it can take longer when used in very dry places because it takes longer to dry and harden.
4 Tips for Using Polyurethane Glue
1. Clean the Surface
At the very least, you’ll want to make sure the surface is clean and free of debris. Oils can also make it difficult for polyurethane to stick to the surface. With soap and water, you can clean the surface to get rid of any oils that have built up.
2. Rough It Up
Having a rough surface can help polyurethane and other glues get a tighter bond and hold better. It will be easier to make the bond stronger if you sandblast metals or use sandpaper on other things.
3. Keep Viscosity in Mind
Decide if a polyurethane with more or less viscosity will make the project easier to do. For vertical surfaces, glues with more viscosity work better than glues with less viscosity. This is because the glue will not run on these surfaces.
4. Clamp It
A lot of polyurethane adhesives make a lot of foam when they start to harden. This foam can push the things that are being glued apart. When you clamp the two surfaces together correctly, this risk can be reduced.
