The Comprehensive Guide To: Polyurethane Adhesives

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FineCal are proud to offer some of the highest quality adhesive products to our valued customers. As well as high quality products, we're proud to provide high quality information, so that we can be certain that our customers understand which of our products are best suited for their specific uses. It's important that you know what you're buying, so we take our responsibility to inform seriously. This week, we’re exploring Polyurethane Adhesives.


Polyurethane close up

Polyurethane close up by Photon_400_750

Polyurethane is a type of polymer that first appeared in Europe in 1937. They actually belong to a group called 'reaction polymers', which includes epoxies, and they are a fairly diverse group of chemicals with many different subcategories.

Some polyurethanes are catalysts, helping chemical reactions to happen faster, while others are used to make insulating foams or even mattresses.

Polyurethane adhesives, then, are simply adhesives that happen to use particular kinds of polyurethane. Like their chemical cousins, the epoxies, polyurethane adhesives are 'structural adhesives', and can be used to create very high strength bonds. They are interesting to us because they are extremely good at joining very different kinds of materials together with a long-lasting and strong bond. This makes them hugely useful for a vast number of different applications, from hobbyist woodworking to car manufacture and home construction.

Why Would I Use Polyurethane Adhesives?

Polyurethane adhesives can certainly be used for woodworking, as the glue bond becomes stronger than the wood in the majority of cases. That means that, depending on the wood, the wood will usually give up before the polyurethane adhesive!

Tests have shown that polyurethane adhesives are stronger than PVA glues (white and yellow glues) in particular situations. If you're gluing the long grain to the long grain, then PVA glues are stronger – otherwise, if you're gluing long grain to end grain, end grain to end grain, or wood to another material such as metal, polyurethane adhesives are theoretically stronger. This is normally solely theoretical – since both PVA glues and polyurethane adhesives form a stronger bond than most woods, the wood should typically break before the shear stress separates the pieces. Either choice is great for wood gluing based on strength alone!

You should choose polyurethane adhesives for wood gluing when there is significant moisture in the environment, you have access to a good pair of gloves, and a setting time of roughly twenty minutes is desirable. Polyurethane adhesives are also generally very weather resistant, so they are good for outdoor projects – since polyurethane adhesives and polyurethane sealants are so tough they are often used on boats, a little rain and sun won't do them much harm at all!

Depending on the specific polyurethane adhesive, it may turn out to be extremely heat- or chemical-resistant, and as such can be used in many situations that would be impossible for ordinary adhesives. However, it is very easy to sand and scrape away from joints, so excess adhesive doesn't have to be unsightly or annoying.

One of its greatest strengths is the variety of polyurethane adhesives available. If you have a job, a polyurethane adhesive probably exists that can handle that job. On the other hand, this can prove overwhelming! If you need help establishing what kind of polyurethane adhesive is right for you, please feel free to get in touch with our staff and ask.

Example Uses For Polyurethane Adhesives

  • Boat-building
  • Car interiors
  • Home repair and DIY
  • Home construction
  • Panel bonding
  • Sub floor installations
  • Serious carpentry hobbyists
  • Carpentry professionals

Since polyurethane's strength is its versatility, it will be most useful for people who need an all-purpose adhesive that is flexible, strong, resistant, doesn't take long to cure, and doesn't need porous materials to work. For some specific purposes, epoxy adhesives will be superior, but polyurethane adhesives have the distinct advantage that they are waterproof.

The Disadvantages Of Polyurethane Adhesives

Polyurethane adhesives are certainly not without their disadvantages. As we have mentioned, they are weaker than PVA glues when gluing wood long grain to long grain, and although it's normally nothing to worry about sometimes it is more than just a theoretical concern. Since long grain to long grain is a desirable joint for woodworking, PVA glues do still have their place and in some cases you would prefer a PVA glue.

Polyurethane adhesives can also be harmful to your health during certain stages in the application process, if you don't take proper precautions. If this worries you, a solid epoxy resin could be an alternative option to look into – but polyurethane adhesives are, in general, fairly safe to use. Just don't get polyurethane adhesives on your bare skin, because they can irritate and damage your skin. Also, please don't breathe in too much, and never get it in your eye!

Most annoyingly, one of polyurethane adhesives' best features – curing in moisture, meaning that it can be used even in wet working environments – can also be a drawback. Leave the cap off the tube for too long, and your adhesive could be exposed to the moisture in the air, harden completely, and be completely ruined. As a rough rule of thumb, expect polyurethane adhesives to be useful for a little under a year, and be sure to prevent moisture getting to the adhesive.

You should definitely clamp anything that is going to be glued with polyurethane adhesives. Although polyurethane adhesives often seem to expand, the foam this creates is not useful to you. It is very weak, and consequently makes the join weaker if it is allowed to force the two materials apart. You have two alternative methods to fix this – find a polyurethane adhesive that is foam-free (they are rare, but do exist), or use a clamp to stop the materials from being forced apart. Using a clamp means that you can choose from the full variety of polyurethane adhesives, possibly saving you money or improving the other qualities of the adhesive types available to you.

Polyurethane Adhesives At FineCal

We understand polyurethane adhesives at FineCal, so if you're still not sure which FineCal polyurethane adhesive would be best suited to your project do give us a call or drop us a line.

Since one of polyurethane adhesive's great strengths is the huge variety of types of polyurethane adhesive, making the choice can seem overwhelming, but some of them are highly specialist and we'll help you cut the list down to a manageable size.

If you still aren't sure whether you need polyurethane adhesives or a different adhesive type altogether, again, we're happy to help! Since we sell such a wide range of adhesives, we're very likely to have a product in stock that would suit your needs.

Last update: Nov 17, 2015


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