Everyone needs a guide, and this article is dedicated to polyurethane glue.

Why do you need it? How do you use it? What’s the best way to apply it? And what materials can polyurethane glue bond?

Moreover, there are several types of polyurethane glues out there, which we’ll talk about.

Polyurethane glue is a special type of adhesive with higher tensile strength than most other glues.

It’s often used for industrial-scale applications and in situations where you want a rigid and flexible bond simultaneously.

Depending on your use, this adhesive can be rigid and flexible.

Keep reading for more information on polyurethane glues!

What Is Polyurethane Glue, and When Did It Appear?

As I said, polyurethane glue is a high-grade adhesive used for weighty applications.

If you need flexibility and rigidity in your bond, then polyurethane is the way to go. It’s based on polymers, replicas of organic chain units related to urethane links.

Simply put, polyurethane adhesives are one-part and two-part.

One-part polyurethane adhesives are already mixed up, and you only need to apply them.

The two-part adhesive needs to be mixed by hand and is a bit harder to use for this reason. That’s why most people prefer using one-part polyurethane glue.

Depending on the makeup of the polyurethane glue, the resulting bond can be rigid or flexible.

This glue type contains polymers formed through polyol and isocyanate reactions.

Polyurethane glue can bond both porous and non-porous materials, so it’s very versatile for the most part.

It was invented by Professor Dr. Otto Bayer back in the 1930s when he discovered polyurethanes.

The man was a doctor researching the properties of plastic, and his discovery was a revolution in the field.

But polyurethane wasn’t popularized as an adhesive until 20 years later. Recently, polyurethane glue has become more and more popular thanks to its versatility and holding strength.

Its flexible and rigid bond is also why people are starting to realize the pros of this glue.

How Does It Work?

Remember polyol and isocyanate? These two components form a reaction, and that’s the basis of how polyurethane works.

However, this only applies to one-part polyurethane glue. The curing process for two-part polyurethane glue is different and will require a few different things.

For one-part glue, a bit of moisture and heat is needed for the curing process to finalize.

When the polyurethane glue is set, it will absorb heat that will fuel the chemical reaction between isocyanate and polyol.

The molecules will intermingle and form a matrix of chemical bonds that’s super strong and durable.

But since polyurethane glue needs moisture to cure, you’ll need to spray the surface with water before applying the glue.

Mist the surface one more after you’ve applied the glue to improve the curing efficiency further.

Now, if you have one-part polyurethane glue, you won’t need to do anything before applying it.

But two-part glue needs a thorough mix beforehand. You have a resin and a hardener in your hand, and you must mix them up.

The good thing about two-part polyurethane glue is that it doesn’t need external help (moisture and heat) to begin curing.

How Does Polyurethane Glue Cure?

Neither of the two types of glue goes through complicated curing processes. But the curing process is not the same, as you’ll see:

One-part Polyurethane Glue

As I said, one-part polyurethane glue needs moisture and heat to begin curing. When the two components are exposed to moisture, the glue starts curing, and that’s when heat is created.

This will improve the curing time, which rounds out to 15 minutes. If you have to correct any mistake, do it within 15 minutes!

As for the entire curing process, this type of polyurethane glue will take between 24 and 48 hours to cure.

The exact time depends on the degree of moisture and the temperature in the room. Polyurethane glue also needs a good clamping until it finishes curing.

This is because the adhesive will foam and expand, pushing the components outwards.

If you don’t want your glued components to fall apart, you must clamp everything together!

Two-part Polyurethane Glue

The curing process is less complicated with two-part polyurethane glue. It doesn’t need any external factors like moisture or temperature to begin curing.

This type of polyurethane has an auto-induced curing process, thanks to the two components you mix.

However, two-part polyurethane glue is rarely used because of its complicated application process.

These glues are notoriously hard to use and quite a bit messy, as well.

Polyurethane Glue Strength

The strength of an adhesive is a very important selling point. It’s what everyone cares about.

Fortunately, polyurethane glue is strong enough to hold most weighty applications in place.

It may not be as strong as some varieties of two-part epoxy adhesives. Those glues are stronger than polyurethane.

But polyurethane glue can remain stable even with 3,500 pounds per square inch worth of weight.

So, it has enough power to offer powerful bonds for most applications. It’s much stronger than wood glue; that much is true.

Moreover, polyurethane glue can bond both porous and non-porous materials.

Lastly, you can sand and paint polyurethane glue once it finishes curing, which can’t be said for other glues.

It remains durable and resilient even if you impact it with shocks and cut it off. Moreover, polyurethane glue is 100% waterproof once it cures completely.

This adds to its overall durability and resilience in time.

Polyurethane glue has a strong dose of UV resistance, as well. You can use it outdoors and indoors for this reason.

What Can You Use Polyurethane Glue For?

Polyurethane glue can bond many materials, including masonry, stone, wood, metal, ceramics, fiberglass, carpets, gypsum, moldings, and various plastics.

Check out my guide on the best wood glues for more tips.

Moreover, some varieties of polyurethane glue can be used for specific tasks and materials.

You should also know that polyurethane glue often comes in varying viscosity and thickness models.

The thicker models are great for stable applications where you need a rigid hold, while thinner models are good for when you only need to apply a thin layer of adhesive.

To offer a few examples of applications where you could use polyurethane glue:

• You can use wood glue because it resists moisture and UV light very well. It also offers a strong bond, making it easy and efficient to bond the end joints of wood together.
• MDF is created from a mixture of polyurethane glue, sawdust, and wood chips. Medium-density fiberboard is one of the most popular materials used for building, and it contains polyurethane glue.
• You can repair dishware using polyurethane glue because, once it fully cures, it’s food-safe
• Using polyurethane glue, you can seal pipes, flooring, and tiles. It acts as a great sealant!
• With a low-viscosity polyurethane on hand, you can bond together metal sheets.
• Using polyurethane glue, you can work in the auto industry and bond windshields to vehicle frames. It’s also often used in the interiors of auto vehicles to attach wiring and other important components.

If I were to name a few brands of polyurethane glue, I would go with Gorilla Glue, E6000, Tremco, Sikaflex, and AP.

These are some of the most popular polyurethane glue brands you’ll find around. I recommend Gorilla Glue and E6000!

Cons of Polyurethane Glue

It isn’t all good with polyurethane glue. It has its downsides. For instance, the substance is very toxic and even carcinogenic before it finishes curing.

Afterward, it becomes food-safe. Other disadvantages include:

• Polyurethane glue will foam and expand, which means you need to clamp down the materials to keep them stable
• If there isn’t enough moisture on the materials, the glue will not cure no matter what
• Limited shelf life (less than one year after being opened). Moreover, moisture will enter the adhesive can and trigger the setting process if you don’t use it.
• It’s extremely hard to remove once it has been set, and you’ll also make a mess.

Speaking of removing unwanted polyurethane glue, there is a way to do it. The glue will stretch and form a super-strong bond, which is generally an advantage, except when it isn’t.

It must be removed fast if it bonds to your skin, clothes, or anywhere else it shouldn’t have.

If you get it on your skin, wipe it away immediately before it has time to dry. After it dries, then the only way you can wipe it off is by scraping it off.

And this means you’ll scrape off the skin too. If the glue dries on other surfaces, you could try soaking that surface in alcohol for a few hours and then scraping it off. Not a pleasant experience!

Either way, it’s already evident that polyurethane glue is extremely difficult to remove once it has dried.

Fun Facts

Adhesives aren’t a fun topic to touch upon. But I gave it my best to find a couple of “fun” facts about polyurethane glue.

One of them is that the adhesive is incredibly toxic and even carcinogenic before it cures. After it cures, it becomes 100% food safe.

It can poison you even if it touches your hands in liquid form.

One more fun thing about polyurethane adhesive is that it can be used in applications that require both rigid and flexibility.

Impact resistance and flexibility come hand in hand when it comes to polyurethane.

It’s quite a paradox to have a glue that’s both rigid and flexible simultaneously.

Wrap Up

Polyurethane glue is a very handy adhesive thanks to its extreme versatility, high-tier tensile strength, and durability in time.

As I said, I recommend one-party polyurethane glue because it’s considerably easier to apply than two-part glue.

This guide should have everything you need to know about polyurethane glue!

If I haven’t answered all your questions, feel free to post below, and I’ll reply as soon as possible!