strength of polyurethane glue - it's strong!

[horst]

Recently a new polyurethane glue came on the market in Australia
called 'selleys liquid nails - platinum' to join it's friend 'selleys liquid nails - floors and decks' which has been available for some years
the first has ultimate strength and is beige in colour while the the second one professed to having super strength and is white
wondering what on earth that meant I decided to some quantitative testing,
I ripped some 6mm plywood to 10mm width and glued them end to end with the white and beige polyurethane glues, and a pair lapped over
like this

out of curiosity I also glued a pair with PVA glue
I left them to cure for a couple of days and the tried to pull them apart
I first used a 10L bucket and filled it slowly with water, didn't get any breaking.. wow wasn't expecting that with such a small contact area
In a rare fit of cleverness as I could see standing next to falling bucket wasn't going to end happily , I decided against a bigger bucket but used bits of steel
and started to fill the bucket until break point
the results
....................PVA.......white PU........beige PU
butt joint.......21Kg........29Kg...........34Kg
lap joint ........34Kg........41Kg...........59Kg

So this isn't actually very scientific because i only had one instance of each, so these are more qualitative
then quantitative results but very interesting regardless I think, first is that the PVA joints were actually quite strong
but a lapping joint of 0.6cm² holding 60KG was just amazing, that's 1400lb/in² for you SI units differently abled people.
I hasten to add that this is a conversion, and may not mean that you can hold 1400lb with a 1" square.
Anybody want to try this with PL premium?

[LelandCrooks]

Glued on the ply face or on the stacked side?

[horst]

good question!
picture updated

[Harley]

I ripped some 6mm plywood to 10mm width and glued them end to end with the white and beige polyurethane glues, and a pair lapped over

Were these joints cured whilst under any form of compression? ( clamp, screws, nails ) ?

[horst]

I ripped some 6mm plywood to 10mm width and glued them end to end with the white and beige polyurethane glues, and a pair lapped over

Were these joints cured whilst under any form of compression? ( clamp, screws, nails ) ?

I held them in place with 4ga screws but not under compression

[Bill Fitzmaurice]

I ripped some 6mm plywood to 10mm width and glued them end to end with the white and beige polyurethane glues, and a pair lapped over

Were these joints cured whilst under any form of compression? ( clamp, screws, nails ) ?

I held them in place with 4ga screws but not under compression

Urethane works best when the joint is secured, though not necessarily under compression, so that as it expands it goes into the pores of the wood. Excess that sits on the surface of the wood scrapes off easily, far more easily than woodworking glue. That which expands into the pores of the wood isn't going anywhere without a fight.

[horst]

the first time I used it I remember wiping some off with a rag and within seconds I had the stuff on my fingers, it has the most amazing ability to creep.
I think not compressing it makes the joint in fact superior, not stronger but more flexible, which is PVAs downfall.

[dmb]

interesting... selleys also have another polyurethane adhesive:

http://www.selleys.com.au/Selleys-Pro-S ... fault.aspx

has anyone down here in oz used this or any of their other 'liquid nail' adhesives for cabinets? The only other polyurethane adhesives i've found here have been the bottled stuff as opposed to caulking gun stuff.

first post by the way, getting ready for an Omni 10 build, and trying to source stuff locally

regards

Darren

[Harley]

interesting... selleys also have another polyurethane adhesive...

We get Selleys here...my personal opinion about Selleys' products....sub-standard, expensive but cleverly marketed.

If yo have Holdfast there, get their Gorilla Grip Express Polyurethane Expaning Glue - here's the NZ link http://www.holdfast.co.nz/pages/product ... psid=20075

Out of all the glues I have tried, this is by far the best. I buy mine in bulk direct ( 4 boxes of 12 tubes ) from Holdfast and it's about $NZ 9.00/tube. I Bunnings it's $15.00, in Placemakers $18.00

[Harley]

Urethane works best when the joint is secured, though not necessarily under compression, .

Not trying to be nit picking here, but for any joint to be held securely when an expanding glue is setting off, it has to be under some form of compression to hold it in place - whether it be a weight, nails, screws or clamps, otherwise it will be forced awa from the joint.

So your "secured" and my "under compression" probably mean the same thing.

I got to speak to an industrial chemist at Fuller Chemicals when they produced the stuff and he knew a lot about these glues, how they were designed and how best they worked. He was the one who insisted that the more the compression, the better it worked, along with moisture, and encouraged me to experiment.

[horst]

it might be stronger if you clamp the joint while curing, but I have a feeling that the thinner the
glue is that there is less capacity for movement before it breaks, this is based on my experience with PVA glues which must be clamped and snap readily when they are subject to flexing, although they are different glues so I may be completely wrong

[gdougherty]

It would seem logical that the less space you have between the boards and thereby the smaller the mass of glue unsupported by wood, the stronger the bond. Dried glue is pretty strong, but it still breaks and scrapes off easily in larger unsupported clumps (dried along the seams). The stuff that's bonded into the wood will take the wood with it when placed under excessive stress.

[lalexb]

(...) Gorilla Grip Express Polyurethane Expaning Glue - here's the NZ link http://www.holdfast.co.nz/pages/product ... psid=20075

Out of all the glues I have tried, this is by far the best. I buy mine in bulk direct ( 4 boxes of 12 tubes ) from Holdfast and it's about $NZ 9.00/tube. I Bunnings it's $15.00, in Placemakers $18.00

Hi Harley, are there many differences between the different kinds of Gorilla Grip PU glues? 10 min/ 1hr / 2hr? Does being faster curing than others make a big difference on the end strength?
I think I used the 1 hr one, can't remember, definitely not the 10min, but it's strong as.... as a Gorilla!!

I've just noticed though that the excess squeeze of glue didn't have the same color as the PL guys' (as seen from the various pics here and there), it's more of a whiter glue than yellow-greyish. Until today I lived in fear I didn't use the right glue for the job... Now that I know the pros are using it, it's such a relief

[Harley]

Hi Harley, are there many differences between the different kinds of Gorilla Grip PU glues? 10 min/ 1hr / 2hr? Does being faster curing than others make a big difference on the end strength?

Gorilla grip Express is a so-called 1hr cure time. In fact full strength is gained many hours after that.

Don't get the 3 minute cure stuff... it's weaker in my experience. I ended up chucking the 3 minute tube.

[haydar]

those living outside USA may hard to find recommended PL Premium.
recently i tried DAP Beat The Nails but it's too thick (like a tooth paste!), difficult to caulk thru joints.
I wonder how viscous the PL is? I imagine it's liquid enough to squeeze into joint easily.
the DAP has stamped date that is expired 3 months though. maybe that changes viscosity?
I found Selleys Liquid Nails as well might try it later.

thanks guys.