The use of adhesive is a must when repairing or constructing a project, whether indoor or outdoor. Whatever the case, everybody wants to get an adhesive that stands up to every situation, such as rain, sunlight, moisture, cold, and heat. What adhesive can give the strongest adhesion for any purpose at any condition?
It’s really tough, but the question demands a bold answer! We observed different adhesive formulas (epoxy, plastic resin, resorcinol, wood glue, etc.), but our vote solely goes to “Polyurethane Glue”! The ongoing PU adhesive guide will make it clear why we’re firmly promoting polyurethane, in addition to exploring some best glues topped with Loctite PL Fast Grab Premium, followed by Gorilla Original Glue.
What is Polyurethane Glue?
As soon as we hear the word “polyurethane”, we see a picture of some popular finishes! Although PU adhesive may have minor similarities in compositions with those finishes, they are generally not the same. It is also different from other adhesives, even in terms of compositions.
What is it, then? Polyurethane glue is an adhesive primarily available in yellow color. It’s polymer-based but contains various adhesive components. But, it is unlike other outdoor glues coming with more than one concoction. You don’t need any mixing; instead, it’s a ready-to-go agent right out of the tube or bottle. However, you will also get two-concoction PU adhesives available in the market.
PU glues are the best choice for heavy constructions, including wood, glass, concrete, and metals that require robust adhesion. Naturally, they’re excellent for light purposes too, e.g., paper, carpet. They can be used as both inelastic or permanently elastic adhesives.
Top Polyurethane Glues – Best Adhesive
Overwhelmed by the long aisle of available urethane adhesives? Don’t know which one to pick? Here we come, as we used to do, with a list of products that work best in all conditions, including cold, and wet for most purposes.
Best Overall (Strongest) – Loctite PL Fast Grab Premium
Runner Up – Gorilla Original Polyurethane Glue
Dedicated Construction Adhesive – Gorilla Heavy Duty
Best for Small Projects – Gorilla Super Glue
Best for Interior – Loctite PL Premium
Best Clear – Gorilla Clear Glue
Best 2 Part Polyurethane Adhesive – Total Boat Foam
Best for Quick Clamping – Titebond Polyurethane Glue
Best Glue for Auto Glass – 3M Windshield Adhesive
Best for Marine – 3M Below Waterline
Is Polyurethane Glue the Strongest?
There is no doubt that polyurethane glue is one of the top three adhesive types. The other two include yellow construction glues and dedicated exterior glues – both fall under the polyvinyl alcohol (PVA) group. We did not consider any hybrid adhesive; in fact, nothing exists more effective than these three. However, ambiguity arises when it comes to deciding whether PU glue is the best among those three. Glue manufacturers and experts have dissenting opinions on that particular point.
One research shows polyurethane glue is the third among them with 3510 psi pressure holding capacity, where yellow construction glue has 3600 psi, and exterior glue has 3700 psi pressure holding capacity. That is their best capacity – only a few can take that probably, and not all the adhesives of a particular category are capable of resisting that pressure.
The other research shows polyurethane glue is the strongest when it comes to end-grain to end-grain joints or end-grain to long-grain joints, where other adhesives have always been lacking. PU adhesives simply outperform PVA (both yellow and exterior glues) or natural protein solution adhesives by all means.
You can use polyurethane glues for almost all purposes, and this is the point where it leaves behind other contenders. They show much better performance than regular PVA adhesives in many areas such as stone, concrete, ceramics, although curing strength is slightly less.
Additionally, polyurethane construction adhesives have shown significant strength in wet and frozen states, proving it to be the best agent for waterproof bondage in extreme conditions. Considering all, we can say – with its compact performance, PU adhesives are the best in all extreme conditions, especially for grain joints. However, if you only want a master heat-resistant adhesive for metals, a single component heat cure epoxy adhesive is what you should prefer.
When to Use PU Glue
As said, unlike other adhesives – wood glue or exterior construction glue – you can use polyurethane glues effectively on almost all substrates, e.g., wood, metal, stone, ceramic, concrete, glass, foam, and many more. They are especially great at combination bonding. Some polyurethane glues are designed for specific applications, while some others for different contexts. Here we’ll learn when you should use polyurethane adhesives.
- When you need to bond different permeable and impermeable substrates;
- When you need the adhesive to set within a short time;
- When you need the adhesive to have good resistance to impact and extreme conditions;
- When the project needs to have a highly flexible adhesion;
- When the adhesive requires to be paintable without performance weakening;
- When you need an adhesive that’s equally effective indoors and outdoors.
Application, Curing, and Dry Time
Start with roughening the surface with sandpaper for better adhesion. Open the tube’s nozzle and apply the glue on one side of the surface, and instantly spread it over the surface evenly. Join both surfaces together as quickly as possible. It’s wise to use screw clamps (if compatible) to fix the surfaces until the glue dries.
Curing is also different from other glues. Unlike others, curing is not done here by the reaction caused by evaporation or mixing of two chemicals; polyurethane glue rather cures by reacting with the moisture inside or on the surface. For safety, you may spray a little water to the surface before applying PU glue.
For clamping, it may require about 2 hours (usually less than that), while you’ll have to wait about 24 hours for perfect curing. The time is pretty much similar whether you paint, stain, or joint. Unless a clear one, PU glue dries translucent.
Processing PU Glue – Safety Instructions
Pay attention to your safety when working with glue. The most common dangers it brings include skin burning, eye irritation, and breathing difficulty. Wear disposable hand gloves, eyeglasses, and a breathing mask to protect your hand, eye and mucus membrane respectively. Glue ingredients are usually believed to be carcinogenic, so ensure enough air inside the room where you’re applying.
Every glue comes with safety instructions, and following those carefully is a good practice. You may contact a veteran or qualified person if you find the application complicated or still have questions.
What to Do If the PU Glue Goes into the Eye or Skin?
If the adhesive comes into contact with your skin, remove it instantly with a clean cloth and thoroughly rinse the area with soap and warm water. You can do the steps vice-versa. If already hardened, use a razor for removal – of course, carefully.
However, PU glue can accidentally adhere to your eye, attaching to proteins on the surface of your eye. It can cause tearing and blurred vision. Rinse the affected eye deeply with water – most of the glue will probably dissociate from the surface.
Where the eyelids have been stuck together or glued to the eyeball, wash the area thoroughly with warm water before applying a gauze patch. Don’t worry – you can expect the eye to open itself within 1 to 4 days without further action. If you find extra red eyes, blood inside the eye, or any sign of infection, do not wait to contact your GP.
Shortcomings of Polyurethane Adhesive
Undeniably polyurethane has grabbed a significant spot on the woodworkers’ shelf. It deserves that. But it has some drawbacks too, though you can manage them with careful use and proper monitoring. The disadvantages include:
- It requires moisture to cure – no moisture, no or weakened curing.
- It expands to fill joints, so measuring the required amount may sometimes be challenging.
- Very short working time, as it may be hard in about 15 minutes.
- When opened, it has a short shelf life ( less than 1 year). That’s not unusual in other glues also, but polyurethane glue being expensive, can cause financial loss.
- Clean up is not that easy – requires mineral spirit or paint thinner.
- As it reacts with moisture, it easily reacts with your body using skin moisture. And the containing isocyanates can cause respiratory problems if not cautious.
What Does Polyurethane Glue Not Stick To?
Polyurethane glue is effective on almost all types of materials, whether porous or non-porous. The list is actually very long and difficult to finish. Therefore, it’s better to know to which this glue can’t make bondage. PU adhesive actually can perform well on polyethylene, polypropylene or substances like Silicone or Teflon.
Storage, Durability and Disposal
When storing PU adhesive, consider the following things:
- Store in a cool and dark room – temperature must be within 10-degree to 25-degree celsius.
- It should be protected from wet, moisture and cold.
- First in, first out – this should be the adhesive processing method.
- Check for packaging damage regularly.
- Cartridge should be well sealed after using it to prevent glue hardening inside the tube.
As said earlier, polyurethane glues have a limited shelf life when opened (less than a year). But when not opened, it can be durable for up to a few years. The enclosed datasheet of each glue will provide you with detailed information about it.
When disposing of, deliver these adhesives to a collection point or container dedicated to taking harmful substances instead of putting those in a regular household-waste container.
Polyurethane Glue vs PVA Wood Glue
Polyurethane and PVA – both are polymer-based adhesives. Both have a variety of applications, including woodworking. But in one place, the difference between them is fundamental – polyurethane glue is effective on any porous or non-porous surface, whereas PVA is only effective on porous wood surfaces. Again, although PVA adhesives are slightly advanced in terms of pressure-strength (about 100 psi more than PU), polyurethane adhesives are clearly ahead in application variety.
Epoxy Adhesive vs Polyurethane Adhesive
Polyurethane adhesives are softer than epoxy adhesives with higher elongation and lower modulus, Tg, and strength. Polyurethane shows excellent performance on cold and standard temperatures (not more than 125-degree Celsius), while epoxy delivers master performance on high-temperature. While curing, they exhibit lower exotherm than epoxy adhesives, resulting in lowered shrinkage.
So, what can the bottom line be? The biggest advantage of this is that it gives the same quality bondage in every case, not more or less like other glues. It works on nearly all projects. Therefore, the use of polyurethane adhesives has been steadily increasing, and it’ll continue to grow, even if the price is a bit higher.