Thread: Polyurethane glue experience - anyone?

Dengy, I tried some made by Titebond a few years ago. Not very impress by it. I also read a strength test article in Fine woodworking or some similar respected source and from my poor memory it was nowhere near the strength of most of the popular "Normal" glues used.
It's one advantage appears to be as a filler.
Not an item I'll ever use again. Save your money.
Cheers, Ian

Like all glues it has its place.

I have used it several times and found it to be really good for the purposes
for which I used it.
I had to extend some external posts and used a scarf joint to do so. In one case
I had to do a second extension (don't ask) where I could not do a scarf joint. in
this case the pieces to be joined were cut straight and square, a hole drilled in the
end grain on both pieces and a piece of copper pipe used as a locator. The big
advantages of the PU glue were/are that it expands, it is easy to remove when dry
as it can easily be pealed off with a chisel, and it is absolutely waterproof. It also
paints very well and does not appear to leave any staining.

Horses for courses.

Thanks for this information, Ian, sound advice. And here was me coming away thinking this poly glue was a new glue on the market, the latest bee's knees wonder glue that was going to solve all my glue-up problems.

A few Googles and checking some back issues of Fine Woodworking indicate it has been around for generations, and that it is best used for laminations and edge gluing where there are no gaps. The gap filling foam of the poly glue has no strength whatsoever. And the mess!!

One article claimed it was far superior for end grain gluing, as it did not get sucked up by the straw-like fibres like PVA was.

Have attached an extract from FWW #180 in Dec 2005.

polyurethane glue.JPG

Originally Posted by Dengue

Thanks for this information, Ian, sound advice. And here was me coming away thinking this poly glue was a new glue on the market, the latest bee's knees wonder glue that was going to solve all my glue-up problems.

A few Googles and checking some back issues of Fine Woodworking indicate it has been around for generations, and that it is best used for laminations and edge gluing where there are no gaps. The gap filling foam of the poly glue has no strength whatsoever. And the mess!!

One article claimed it was far superior for end grain gluing, as it did not get sucked up by the straw-like fibres like PVA was.

Have attached an extract from FWW #180 in Dec 2005.

polyurethane glue.JPG

Looks like the grey cells aren't so bad after all.
I was pretty sure it was FWW, glad to see you found the article.
Cheers, Ian

The expanding PU glue is also for exterior use. PVA won't do outside so well.

I used some to make a bedroom suite out of brushbox a few years ago. I was told brushbox has exudates which make it hard to glue with pva etc. Nothing has given way in 10 years so I guess the bond is adequate - its a bit harder to use though and you get sick of cleaning up the squeezeout. Its other advantages are its waterproofness and the fact that it will stick tiles, metal etc to wood.
I havent used it since because unless you need these advantages then conventional pva glues are better.

Incidently, I find modern pva's are good for end grain gluing - you just have to apply a couple of sealer coats first to overcome the tendancy to suck the glue away - then the bond is as strong as long grain or maybe stronger.

I've used this a few times and again, in the correct application, it's great. It reacts with moisture to cure and expands quite alarmingly; you need to make sure it's securely clamped. Waaayy back in around 2004 Australian Woodworking Review (or it might have been Australian Woodworker!) did a review on it; one of the tests was to glue a piece of end grain to face grain in a "tee" shaped butt joint. When it had cured they then broke the joint and found that the face grain had let go, not the joint and not the end grain! Where it really shines though is glueing different materials together like wood to brass.

One truly great use for this glue is in pen making, as taught to me by Willie Nelson (not the singer; the old duffer residing in Jarrahland, WA). When you're making pens from burls you often get cavities and voids in the grain structure of the blank; poly fills these up and gives support to the surrounding timber; this comes in real handy when you're turning the piece as it severely reduces the number of blanks that either explode or just fall apart as soon as the chisel touches them.

Block off the ends of your brass tube with a piece of potato (just cut a slice 1/4" thick and use the tube like a punch) and smear poly all over it and inside the hole drilled through the wooden blank. Work the tube in and out to ensure the glue coats every surface, then leave it to cure. The potato stops the glue from entering the tube, and the glue foams up and fills any slight imperfections in the drilled hole. Works brilliantly.

Lastly, keep some acetone on hand as that is what you need to remove spills. Wear gloves too unless you want your skin to turn black.....

Here is a link to an article by Christopher Schwartz on this poly glue

The Truth About Polyurethane Glue - Popular Woodworking Magazine

In my personal experience, it's the beginner's go-to when joints are really, really sloppy. I've spent a LOT of time improving my skills to the point where 'gap-filling' glues are rarely a necessity and other glues - such as PVA - become the choice for reasons of bond strength.

Unless you're gluing end-grain (in which case it may be stronger, although I've never seen any test results... just claims) but you're not going to open yourself to ridicule by telling us that you often glue end-grain to end-grain, hmmm?

Mind you, I still use the stuff for many odd jobs. eg. It works extremely well when making tool handles... gluing a square rod into a round hole, for example.

So it has it's place on my shelf: just not for gluing wood together any more.

PU glue is NOT gap filling and don't let anybody tell you otherwise, if anything, I'd say that PVA is better at gap filling as you end up with a solid chunk instead of the foamy stuff. I've read the data sheets on several PU glues and they all give the maximum allowable gap as 0.5mm or less. If you want a gap filling glue, stick with epoxy. (Sorry about the terrible pun, but I'm not changing it) That being said, I've seen many people say that PU is gap filling, so I'll try and remember to do some proper testing of this and post the results. As for end-grain to end-grain and end-grain to edge-grain; I'll test that as well, but I don't think it's really relevant as no one does that without dowels/domino/dovetail keys anyway (please tell me this is true).

PU is great for laminating as the join lines are thinner, take stain/polish better and don't 'creep' like PVA, PVA glue lines themselves sometimes swell too, this won't happen with PU. It's also great for outdoor applications as it's 100% waterproof, not water/weather resistant. It's also great for oily/waxy/resinous timbers like blue- and spotted-gum and teak.

The main downside of PU is, as mentioned by others, it has to be properly clamped for the duration of the cure time - which is usually faster than PVA anyway.

All the above is based on over 5 years of using the stuff in a commercial/industrial setting.

Hi Dengy
Here is the link to some tests and a chat about glues I put up a few years back. I don't think much has changed since. Same brands etc are still relevant.

https://www.woodworkforums.com/f198/s...-tests-119072/

Thanks guys. On the basis of this information above, I don't quite have confidence in the Poly glue that the guys in the Mens Shed do, so I have returned the Selly's Durabond to Bunnies, and got some Selley's Aquadhere PVA ( External) instead

Yep, I have been using the Selleys PVA External on everything (wood) since then and have no trouble inside or out. I buy the 4ltr
container but unless you use that much in 12 months or less I would stick (haha) to the smaller bottles and have fresh glue.

Originally Posted by Dengue

Thanks guys. On the basis of this information above, I don't quite have confidence in the Poly glue that the guys in the Mens Shed do, so I have returned the Selly's Durabond to Bunnies, and got some Selley's Aquadhere PVA ( External) instead

As elanjacobs said, PU glue is great for oily, waxy or resinous timbers that can repel water based glues. It also works well to glue metal to timber. Also my experience with laminating is the same as his, but you need to use one with a decent open time when laminating.

Good clamping is essential. If we rely too much on it's so-called gap filling properties, we will be disappointed. It fills the gaps ... with foam ... that you can pull apart with your hands.

Cheerio!

John