Thread: Thinning Polyurethane Glue

Interesting idea - not sure if it can be thinned without affecting the strength/cure, but will be interested to hear if anyone has tried this.

I have to say I'm not entirely convinced about PU glues generally. I started out using Techniglue for laminations (too gluggy, has to be spread with a scraper), then tried various PVAs, and have finally settled on West System epoxy which is thin enough to be applied quickly with a foam roller. The thing I like about West System is that there are several different hardeners to go with the one resin, so I can chop and change hardeners depending on the speed of cure I want. The slow cure one is very useful in summer for multiple laminations !

I picked up a small sample of Purbond from the Boatcraft guy at the Canberra WWW show - this is the thinnest PU I've seen, and might even be spreadable by roller? Trouble is the test joints I've done with it (even damping the substrates first) haven't resulted in very good strength, and have a more noticeable glue line than epoxy. The jury is still out on this one; I'll be giving it more of a try when I have some time.

If all else fails you could give the Boatcraft guys a call; they probably know more than most about what can and can't be done with PU glues.

John, from the destructions on the bottles:

Titebond PU: Open time 30 mins, clamp time 1-4 hours (fully cured after 4), wash hands with soap & water, clean up tools with mineral spirit.

So, I'd be inclined to try diluting it with water as a test to see what happens. If it won't mix or fouls up, then try a bit of mineral spirit. (turps or white spirit?). I've often cleaned up with turps. Great glue - as you say, metal to wood.

Titbond 3: Clamp time 30 minutes, do not stress joints for 24 hours. No open time mentioned, but can't be more than 30 minutes (like TB 2)


However, bear in mind that PU is hell expensive, and TB 3, whilst more expensive than TB 2, can be purchased in larger quantities. Titebond also claim that it is stronger than their own PU.

Originally Posted by FenceFurniture

John, from the destructions on the bottles:

Titebond PU: Open time 30 mins, clamp time 1-4 hours (fully cured after 4), wash hands with soap & water, clean up tools with mineral spirit.

So, I'd be inclined to try diluting it with water as a test to see what happens. If it won't mix or fouls up, then try a bit of mineral spirit. (turps or white spirit?). I've often cleaned up with turps. Great glue - as you say, metal to wood.

I had read somewhere else a suggestion that the PU be thinned with water, but given that dampening one surface accelerates the cure time with the Selley's product, I suspect the same thing might happen with Titebond PU if it is thinned with water, but it is worth a test.

Never used West system epoxy ... but am going to Carba-Tec today. Might pick up some Titebond PU and West epoxy and do some trials.

No glue is great in every application, but I have had good success with the PU where I have used it. I'm sure it bonds better to end grain (as in breadboard ends) than PVA, but so far have not run any tests, so I think it is time that was done. There is no substitute for tests and data.

Highly recommend TimbaTec PU, we changed from Purbond PU about a year ago at work after we started having de-lamination problems with the Purbond (we still can't work out why as we were on Purbond for over 5 years with no problems). It spreads easily from room temp down to about 8 degrees without heating (melbourne winter sucks) and is half the price of Purbond - $25 for 1L vs. $40+ for 700mL. We also did some water/weather resistance tests last summer involving soaking glued pieces in water for a few weeks, then leaving outside for a few weeks and the TimbaTec performed consistently better.
It comes in 3 different work/clamp/cure times: 5/15/60min, 15/60min/6hr and 30min/5hr/12hr and, according to the data sheets, there's no difference in strength. One warning on the 5hr; the squeeze-out goes rock solid and has to be removed with a belt sander, scraping (which is nearly impossible) will rip out bits of timber on the joins. If you don't need the massive working time, don't bother with it.
Also 100% Aussie owned/made if that makes a difference.

Who sell TimbaTec Elan? Had a look on the website, but it doesn't say.

I think you have to go direct to the manufacturer.


Factory 7, 13-15 Crawford Street
3195 Braeside, Victoria
Phone: +61(3) 9587 0509

That TimbaTec sounds worth tracking down - will have to give them a call.

Thinking of another application, which would be better for outdoor furniture applications (i.e. lots of UV + water) - epoxy or polyurethane?? I'v always used AV515 PU for outdoor timber jobs around the house in the past, although it is far too thick to be used for laminating. Titebond III may be rated 'waterproof', but a test piece I left out in the weather started to come apart after about 12 months exposure to sun and rain. I know that Titebond III PVA isn't really intended for true "all-weather" use, but would epoxy or PU be the better choice?

Cheers.

Epoxy only bonds the surfaces, while PU expands and pushes into the pores of the timber as well; don't know what, if any, difference it makes, just something to think about.
Also, epoxy (at least the thicker stuff) shouldn't be clamped too hard as that pushes it all out of the joint - thereby defeating the purpose of gluing in the first place - so you end up with a bigger glue line.
The only real world difference I can think of would be how well the glue lines will take a finish, and even that will only be a problem with oil finishes that are absorbed into the timber. Epoxy will also be more likely to crack as the timber moves.
I don't like epoxy for furniture in general, but that's just a personal preference.

Originally Posted by elanjacobs

I think you have to go direct to the manufacturer.


Factory 7, 13-15 Crawford Street
3195 Braeside, Victoria
Phone: +61(3) 9587 0509

Thanks, elanjacobs.

I'll give them a yell. the 15/60/6 version sounds like it will do the job for me, but I might get some 30/5/12 for the odd occasion when I need a much longer open time.

I still use PVA for most work. However, I am finding many applications for the PU as time goes by. Single pack ... very rapid cure time (with the faster stuff) ... good sanding ... chemical cure rather than "dry out" action ... less creep in the joint ... bonds wood to metal. If, as I suspect, it is superior at glueing end grain, there is a lot to like about this glue.

It is brilliant at edge glueing shop sawn laminates. Wet one edge ... glue the other ... and 20 minutes later it is scraped off and going through the drum sander.

If no-one has run end grain tests (like bread board ends), I just might give it a go ... once I figure out how to measure the force at failure.

I was re-reading the instructions for Purbond (a bit drastic, I know...) to see if I can work out what I'm doing wrong. It actually says the joint should be very firmly clamped, unlike epoxy as someone else mentioned. This probably applies to all PU adhesives. Maybe I haven't been applying sufficient clamping force?

I'll also try some test joints with a bit less moisture applied, i.e. lightly wipe with a wet rag then leave to almost dry before applying the glue.

I seem to remember that there was a group test of glues in Fine Woodworking a few issues ago, and they concluded that PU adhesives gave a weaker bond than most of the PVAs and epoxies tested?

Originally Posted by Mr Brush

I was re-reading the instructions for Purbond (a bit drastic, I know...) to see if I can work out what I'm doing wrong. It actually says the joint should be very firmly clamped, unlike epoxy as someone else mentioned. This probably applies to all PU adhesives. Maybe I haven't been applying sufficient clamping force?

The first time I used PU glue was on greasy/resinous NG Rosewood. (I always firmly clamp PVA and PU glue seams.) PVA was being repelled, so I tried the PU (used the Selley's Tarzan's Grip product because it has a fast cure). It worked very well. I tested the off-cuts. All of them split the wood rather than exhibited failure along the glue line. So, the seam was stronger than good quality NG rosewood, but even PVA glue will do that. However, if the glue line is stronger than the timber ... it's strong enough. Under most circumstances, any added strength is wasted.

I'm told that because the PU is a chemical cure (rather than a glue that "dries out") that it suffers less "creep" than PVA, but this is hearsay at this stage.

Usually, I only use a damp rag to very slightly moisten one surface. Very little moisture is needed to catalyse the glue. The exception is when making a biscuit joint when both sets of grooves are glued up. The biscuits are dropped into water for a second or two, wiped off with a dry rag, inserted and the joint is clamped. This is done so the biscuits will still swell and fill the joint ... that's the theory anyway. I have yet to test it.

Thanks for the info John - more grist to the mill.

I'll try to get the stuff working reliably on normal joints before I even consider how to use it with dominoes.....

Originally Posted by John Samuel

I'm told that because the PU is a chemical cure (rather than a glue that "dries out") that it suffers less "creep" than PVA, but this is hearsay at this stage.

Usually, I only use a damp rag to very slightly moisten one surface. Very little moisture is needed to catalyse the glue.

PU will creep less than PVA (not sure if it will actually creep at all)

Wetting the surface(s) before joining is not necessary at all, there's enough moisture in the timber. You only need to add water to speed the cure time, which only helps a little bit

Originally Posted by elanjacobs

PU will creep less than PVA (not sure if it will actually creep at all)

Wetting the surface(s) before joining is not necessary at all, there's enough moisture in the timber. You only need to add water to speed the cure time, which only helps a little bit

Hi Elan
I have also had delamination probs with poly glues, what species of timber are you gluing up.