PVA and Polyurathene wood glues

[chippy minter]

Can anyone please explain the different caractoristics of the two glues, and where would you use them .

 

[Scrums]

PVA is a water soluble glue available in (when dried & set) various amounts of 'waterproofness'. I think the D1, D4 used often on the labelling refers to this. It won't cure properly below a certain temperature and around that temperature leaves 'chalk lines' around the joints.

Polyurethane or PU glue is waterproof, very strong and sets quite quickly and also sets at temperatures a little below those of PVA. It has good gap filling properties and will stick any one porous surface to any other - ie wood to metal. Because it foams and expands when setting it always needs clamping, for instance I've used it on magnetic knife racks to fit 10mm dia rare earth magnets into a hardwood batten and unless you drill a small through hole, it will push the magnet out. PU has a limited shelf life - 6 months? and turns your fingers black (mine anyway) which stays for a day or so. The only cleaner/solvent I know of is Acetone. It is also a bit more expensive than PVA.

Hope this helps, I use it all the time nowadays.

Chris.

 

[johnnyb]

according to fine woodworkings tests pu glue is really quite poor in comparison to almost all glues(for woodworking) it came bottom for nearly all tests, these included open grain, close grain, loose joint, tight joint, perfect joint. basic pva had a very good showing as did hot and cold hide glues on open grain timbers(oak etc) this was a quality article well worth a read.

 

[Scrums]

.....gobsmacked!.....I rate it very highly and have never had a problem.

 

[Philly]

Found the recent FW results strange - seem to contradict earlier tests. I also have great results with PU glue.
Maybe Titebond sponsored the tests...... :wink: :lol:
Philly

 

[Oryxdesign]

By the way when it foams it produces a gas, which is probably bad for you.
I use it too sometimes and am surprised by those results.

 

[andycktm]

It's always going to be painful being told cheaper glue is better than
more expensive glue.(If you use the more expensive glue that is).

 

[Digit]

Living, as I do, close to the Atlantic coast, timber can take a real battering. 60 F is shirt sleeve weather and 70 is indecent exposure, then the rain pelts down to get under the paint that the Sun has blistered. I have built a verandah and twin gates in Oak, all glued together with PU. They have stood everything for 5 yrs now and not the slightest sign of trouble.

Roy.

 

[andycktm]

But if you build an oak coffee table for indoor's?
Do you need PU? or is cheaper PVA the way to go.?

 

[Digit]

Well there's PVA and PVA. I found, to my cost, that the white PVA stains some red woods, I switched to Titebond and have used it ever since for indoor work.

Roy.

 

[andycktm]

Ok Roy,so PVA it is In your opinion where do you switch to P.U,
Bad fitting joints ,out door, severe weather.
I'm just putting an oak coffee table together and was tempted to try P.U
Why? i thought it was better than PVA glue :?

 

[Digit]

I don't admit to bad fitting joints! :lol:
Indoors I have used Titebond for all sorts of constructions from small clocks to very large cabinets in soft and hard woods and have desire to change.

Roy.

 

[Pecker]

I have been using PU glue for about 4 years now. I've used in in every conceivable situation, including to glue 5 mtr long 5" x 5" beams made in box section and glued together. That was 2 years ago.

I've got about 30 external gates stuck together with Pu that are still going strong.

I still use PVA, especially for nice joinery as it doesn't expand and mark the wood.
But I find it amazing that Pu came out bottom for every class. Last week I posted on here about testing Pink grip angainst PU.
We tried various tests including PVA. We glued strips of Stirling board 3" wide by 12" long together with a 6" overlap.

The PVA did indeed hold well, but the PU was literally unbreakable.

I really do find those results strange.

Woody

 

[Digit]

Perhaps they weren't using it properly. Nobody on this forum seems to have had any problems with PU, my only complaint is the limited shelf life.

Roy.

 

[andycktm]

Has it gained a blind following :!:
Anybody from Fine Woodworking care to comment?

 

[Harbo]

There's a comprehensive article on glues in March's issue of "The Woodworker" which is not quite as damming against PU, but they also found that although the glue expanded to fill gaps it had very little strength in that situation.
Their recommendation was PVA (for general use and cheaper cost), then Titebond 3 as the most versatile and then Polymite (Cascamite) for slow setting and non creeping therefore ideal for veneering and stressed joints.
It's quite an interesting read and covers a wide range of glues and explains where best to use them.

Rod

 

[Jake]

ut they also found that although the glue expanded to fill gaps it had very little strength in that situation.

That isn't news, the manufacturers (of the products I've used) have never pretended otherwise (in the instructions, they mention this).

 

[Pecker]

Andy, I really like PU, and my employee swears by it. BUT it DOES expand. To get the best out of PU dampen the wood down a tad 1st. It will stick like ****, but will also expand a lot. So, either clean the wood off very well afterwards, once it has expanded, or use good quality pva then clean it off straight away.

Tony, my employee, reckons it can be easier to clean off the pu sometimes then the residual pva leaves, but that might be personal opinion there.

He has just made a lovely oak table all held togtehr with pu.

By the way, I was informed by a sales manager for Evode, that the blackening to the skin caused by PU, is actually skin pigment reacting with it's constituants.

I'm not disputing it, but I personally have not heard of any gases being produced by PU, and some days we get thru 10 tubes in our small workshop with no noticable ill effects - certainly far less than compared to solvent based adhesives.

woody

 

[andycktm]

So that's it eh,Gaps all over.pva hides nothing,pu is expanding foams brother

 

[Jake]

Not really, both require a good tight joint to work.

PU's main advantage is speed (and it tends to be D4, which very few PVAs are). It goes off in minutes, rather than hours.