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Polyurethane glue question. - Sawmill Creek Woodworking

07 Jul.,2025

Polyurethane glue question. - Sawmill Creek Woodworking

Does anyone know if polyurethane glue will bond with cured finishes? I have some finished plywood and I would like to add some spacers to it. I don't want any nails or screws in the way so my only real choice is glue... if that will work. Expoxy will work (I've done it before), but I have about 24 lineal feet x 1.5 inches to glue and don't want to mix that much epoxy (or spread it for that matter).

How about urethane resin glue?

Any help would be appreciated.

Bryan Well, you don't always have to clamp. You could use weights.

But do keep in mind that although poly glue will probably stick it OK, you have to think about how you're going to clean up the foam that comes out. If you're trying to avoid using screws because they're unsightly, having scrape marks from cleaning up poly glue isn't going to be desirable either.

If you use epoxy, you don't need to mix or spread that much of it. You don't need to cover every square inch of a large face-to-face joint. Just a blob here and there will do. Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank

Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank

I'm wondering if the oily qualities of the teak were what did it in ultimately, even polyurethane construction adhesive (gorilla glue's much meaner big brother) doesn't do well when the surface has even the smallest bit of oil contamination. >> This will be used in an area that will be difficult to clamp, not impossible, but difficult.

The question you have to consider is how strong do you want the bond to be? Or, need to be? Poly adhesive will have less strength if applied over anything other than virgin wood. It will be stronger than PVA but not as strong as an epoxy.

Another point, poly adhesive REQUIRE clamping. As they react with moisture they foam exerting quite a bit of pressure toward opening the joint. If foam forms in the joint the joint is significantly weakened.

Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank

Poly is touted as being able to easily glue oily woods but I've no experience there. I've used poly on several projects (all indoor stuff) and haven't had any issues so far.

I'm curious how you knew it was glued with poly. Are you sure? Just checking. Roo Glue won't stick well

Polyurethane glue like Gorilla sticks pretty well to anything I've ever tried it on. It'll probably stick to your finish. Another glue which you might try is Roo Clear. It is intended to glue melamine. Gorilla foams up as it cures, so you must be able to clamp your pieces together. If you're working in the middle of a sheet of plywood, that may be difficult. Roo Clear doesn't foam, so it would be better in that situation.

I tried it on some prefinished maple ply. It sticks, but not well in my experience. I can't say about polyurethane.

HTH

Curt

Best Practices for Using PUR Hot Melt Adhesives - LD Davis

Polyurethane reactive glue, or PUR, is a synthetic material used frequently in volume manufacturing and home repair. First invented in the s, polyurethane hot melt was used as a less expensive alternative to rubber but has since been refined and has expanded to be one of the most popular adhesives in manufacturing. So why is PUR adhesive so appealing, and what are the best practices for using PUR hot melt in your production?

Read more

Why choose PUR Hot Melt for your application?

Although hot melt adhesives have been around for decades, advancements in PUR development have made it popular for applications like bookbinding, woodworking, and packaging starting in the s. Since it is highly flexible and has a broad thermal setting range, PUR is perfect for bonding difficult substrates.

Significantly stronger than traditional hot melt, PUR hot melt provides adhesive strengths greater than 1,000 lbs! This is due to the PUR polymerizing when it comes into contact with moisture in the air. The crosslinking polymerization causes the adhesive to form a stronger bond than other hot melt glues after the curing process is finished.

PUR also has a low volatile organic compound (VOC) content when compared with other hot melt adhesives, making it a more eco-friendly alternative. Most PUR adhesives do require 24 hours to cure fully, and their strength is increased by reacting to moisture in the air, so it is vital to expose PUR to air during the drying process.

Key Characteristics of PUR Hot Melt

Creates a bond stronger than 1,000 lbs
Flexible and can be hard set or rubbery once cured
Works with hard-to-bond, nonporous substrates
Tolerates a wide temperature range, making it suitable for indoor and outdoor use
Works well with difficult substrates, coating, and inks
High-quality bonds can be made using less adhesive than other hot melt glues
No mixing is required
Fast curing time

Popular Applications for PUR Hot Melt

While many industries are using PUR hot melt in their manufacturing process, we are frequently asked how a business can incorporate PUR into their production. Hot melt adhesives are applied in many industries to maximize ease of use, reduce labor time, and take advantage of temperature and moisture tolerances. Every industry is different, and we listed some of the most popular applications for PUR hot melt below.

Bookbinding

PUR adhesive is often used for perfect binding. While traditional perfect binding uses EVA glue or animal glue, PUR is an effective and efficient alternative. Using PUR adhesive makes bookbinding more durable and causes less cracking because the glue is more flexible after curing than EVA or animal glue.

Packaging

PUR hot melt provides a stronger bond and a faster cure time than some traditional hot melt glues, making it popular with industrial packaging manufacturers for applications from shipping containers to cosmetics.

PUR can also dry clear, making it easy to hide glue lines and give the appearance of continuity in a glued material.

Woodworking

Using PUR to assemble wood furniture can help eliminate the need for additional screws and fasteners.

Many craft makers turn to PUR as their go-to adhesive because of its fast drying and high strength properties.

Construction

Due to its ability to bond to non-porous substrates, PUR is great for use in construction. Its high strength can hold hard-to-bond materials together without additional fasteners. PUR adheres to wood, glass, plastic, and most metals. Its fast drying time and bond strength make PUR a suitable adhesive for automated assembly as well.

Best Practices for Working with PUR Hot Melt

1. Safety first—hot stuff coming through!

At some point, you’ve probably accidentally burned yourself with a hot glue gun used for crafting. Now imagine touching a larger industrial closed melt dispenser between 180°F to 280+°F. Ouch! Commercial hot melt like PUR needs to be handled with care, and you should protect your skin from molten glue using gloves and safety glasses. Be careful to not touch the adhesive applicator’s heat cylinder, cartridge, or dispenser when in use. Also, do not apply PUR to heat-sensitive materials.

2. Test for success

If you want to learn more, please visit our website BGP.

Before starting your project, test how well hot melt adheres to your chosen substrate. Apply a little bit of hot melt to a piece of scrap material and wait for it to cure before tackling larger aspects of your project. By taking the time to test, you can understand if PUR hot melt is right for your current project before committing to gluing it together.

3. Proper Storage

To extend the life of the glue, store it in a cool, dry place. PUR adhesive most often comes in slugs, pails and drums, which are closed systems to help preserve the glue. The standard shelf life of a PUR glue is about one year.

If you are having any difficulty using or storing hot melt, the experts at LD Davis are here to help! Check out our hot melt troubleshooting guide.

PUR Hot Melt vs. EVA Hot Melt

Those interested in how best to use PUR hot melt have probably come across EVA adhesives and wondered, what’s the difference between the two? Both types of glues are suitable for perfect binding and packaging, but PUR is the more durable of the two and offers better flexibility and durability for all applications.

Benefits of EVA Adhesives

EVA glue uses an open dispensing system, which requires less of a start-up cost for manufacturing. EVA glue also has a faster drying time, lasts longer, and requires less cleanup; however, it is less flexible than other hot melt glues. Due to its fast cure time and ease of use, EVA hot melt is popular for use in bonding applications like packaging, graphic arts, and general assembly work.

Benefits of PUR Adhesives

PUR glue uses a closed dispensing system to heat the adhesive and then disperse it onto the desired substrate to dry. PUR adhesive takes longer to harden than EVA because it requires exposure to moisture cure, but it creates a stronger, more flexible bond in the end. The strength and flexibility of PUR hot melt make it the go-to choice for perfect binding, general assembly, packaging, and woodworking.

Perfect Binding With PUR Hot Melt

Technically, PUR binding is perfect binding; it’s just accomplished using PUR glue rather than EVA. Perfect binding is a fast and inexpensive way to bind paperback books by gluing the pages together at the spine. Because of the 1,000 lbs strength of PUR combined with its flexibility, PUR hot melt has quickly become the preferred adhesive to use for perfect binding because it can hold up to repeated use and requires less adhesive than EVA.

Working with specialty papers, inks or coatings? PUR is a great adhesive to use because it is less affected by tough-to-bond substrates. Another benefit of PUR glue over EVA for perfect binding is the lay flat capability, which is especially favorable for photo book binding.

We’re often asked by customers, can you use PUR glue in a perfect binding machine, and the answer is yes! PUR requires a closed system for perfect binding to keep it from interacting with the moisture in the air.

Want to know more about using industrial polyurethane glue?

If you are interested in using PUR glue in your project, want to know how PUR hot melt can compliment your manufacturing process, or are looking for a glue supplier, contact the adhesive experts at LD Davis.

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