Cascomite and Green Oak Problem

[deema]

Just had a gate I had made in green oak (c25% moisture) fall apart after three years. I went back to it and every single joint had failed. It was just as though the glue had completely disappeared. Very little in evidence. It was well glued at the time of construction. The only issue I can think of was that it was made in Winter, however I don't believe the glue froze vernight

Has anyone had a similar problem? Know of any issues with my favourite glue? Never had a problem like it.

 

[Peter Sefton]

Here is an extract from the data sheet on the UF we use.


Ideally the moisture content of the substrates should be 10-14% with no more than 3% difference between the two surfaces to be bonded, otherwise stresses are built into the joint which may result in wood or joint fracture.

We don't use timber with high moister contents but if I was undertaking a project with high moisture content I would use a PU expanding glue as it need's moisture to cure.

I am sure someone with more experience of this will come along soon.

Cheers Peter

 

[Hand Plane]

I had all the joints in a chair fail - somewhat embarrassing.

I was eventually advised by the manufacturer that the glue has a shelf life of possibly two weeks once the container is opened!

There is no notice to this effect on the container.

 

[Random Orbital Bob]

The cascamite I use is powdered so that cant have a shelf life as you mix it when you use it.

 

[Phil Pascoe]

No. The powdered Cascamite deteriorates as soon as it's exposed to air. The best thing to do with it is to immediately put it into smaller containers when opened. It doesn't mix the same way when too old. It was noticeable 45yrs ago (this was at school) when I first used it that it would shatter in the joints of chairs, so we always used PVA for small, stressed joints.

 

[Random Orbital Bob]

Interesting. I would never have fathomed that from a powdered glue. You would think the whole point of it being in powdered form would be to preserve it wouldn't you?

 

[Phil Pascoe]

There's a thread here dealing with it, somewhere.

 

[CHJ]

The cascamite I use is powdered so that cant have a shelf life as you mix it when you use it.

Yes it has, if it is exposed to air with normal household moisture content, I.E. an opened container with a significant air gap. then it will deteriorate in a few weeks.
Usual indication is that it will not mix to a creamy constituency and takes on a crumbly appearance.

As for the Failed Gate Joints, has the hot dry summer shrunk the wood and opened up the joints, if the joints were a good fit then the glue line would have been thin and virtually invisible once failed. Cascamite is very strong but has no flexibility to creep or move with the wood

Must admit I've never contemplated glue joints for external doors and gates and just relied on drawbore M&T's

I can break a cascamite joint between two pieces of restrained Oak by reducing the moisture content from 15 to 8 % **
** Testing construction methods for segmented turnings. (wood surface fails)

 

[Peter Sefton]

It should last between 12/24 months if looked after but only a couple of weeks if in damp conditions.
Not all Cascamite is the same some poor quality UF is now on the market.

 

[cornishjoinery]

Green oak and glue doesnt go. Like someone mentioned above, a gate used with green oak should be mortised and tennoned then drawbored. There is no need for glue what so ever.

 

[yetloh]

Quite apart from the glue deterioration possibility, I think there are two other possible issues here.

The first is the moisture content of the wood. Like PVAs, UF glues rely upon the right amount of moisture and this is essentially the amount in the product as it comesout of the container whether that is out of the bottle or correctly mixed powdered glue. A high moisture content in the wood will lead to localised dilution and and therefore a weak joint. I had some correspondence with Titebond about this and they told me they cannot recommend their glues for wood with a m/c of more than about 15% for this reason on the grounds that with very high m/cs the joint might never set up at all. I'm no chemist but it seems logical that UF glues might have similar pproblems.

The second point is that gates are often subjected to quite a lot of twisting stresses and UF glues set glass hard with very little flexibility. I'm afan of UF glue, not least because of its long open time, but I wouldn't use it on a gate or chair because of the flexing stresses alone. I have recently been making some steam bent laminated chairs in green ash and after much research settled on Purbond HB110 which is a PU glue with up toan hour's open time and the results have been excellent. Purbond is extremely flexible and also colourless but is unfortunately not readily available in the UK (although you can import it from Switzerland) but I am sure there must be other PU options out there. The obvious one would be Gorilla glue but that has an open time of only 10-15 minutes making it unsuitable for complex glueups.

Jim

 

[swb58]

Green oak and glue doesnt go. Like someone mentioned above, a gate used with green oak should be mortised and tennoned then drawbored. There is no need for glue what so ever.

I don't think the guy who made the gate understood the concept of working green wood, joints are supposed to tighten as the timber dries.

 

[owenmcc]

We don't use timber with high moister contents but if I was undertaking a project with high moisture content I would use a PU expanding glue as it need's moisture to cure.

I am sure someone with more experience of this will come along soon.

In this instance I've experience but not knowledge. Playing around in the workshop when working on green oak frames we glued some bits together. My thoughts were the same, PU needs moisture, green oak is moist, this should work.

Our small tests would suggest it doesn't, even under day long clamped pressure planed green oak could be torn apart, sawn and split could be broken along the glue line easily.

The reason for testing this was for repairs and splits (which clearly need to stop happing) and I'd add my +1 for the mortise/tenon/peg approach to green oak.

Anyone with the knowledge for why PU and green oak don't work, or under what conditions they would?

 

[Sgian Dubh]

All but one type of the common woodworking adhesives are formulated for dry wood applications. Dry wood is 20% MC or below, so using PVA, urea formaldehyde, hide glue, etc on green or wet wood is fairly certain to fail. The only adhesive that does work well in this circumstance is polyurethane formulations of adhesive. We have been using it for many years in this situation for artefacts made out of green or partially dried oak destined for exterior locations. It works well, but I can't say if polyurethane adhesive was designed specifically with this sort of application in mind or if it's simply a bi-product of the way it cures.

But as cornishjoinery said above your joinery for this type of application really needs mechanical locking so that glue isn't the only thing holding everything together, which is the method we use even though we frequently include glue as well.

owenmc, I can't explain the reason for the failures you experienced. They are at variance to mine, and contradict the experience and extensive testing of polyurethane glues in green wood situations undertaken by a contact of mine at the Building Research Establishment (BRE). In the following link the first reference to the type of glue used is on page 8. Slainte.
http://www.forestry.gov.uk/pdf/225831_i ... _phase.pdf

 

[Phil Pascoe]

I've never quite understood how a mortice and tenon (say) in green wood tightens as it drys. If the piece with the tenon was bone dry and the piece with the mortice green, the green piece would shrink around the tenon as it dried and the piece with the tenon would expand . But no one is going to use timber half of which is dry and half of which is green - so how does this work?

 

[Peter Sefton]

I've never quite understood how a mortice and tenon (say) in green wood tightens as it drys. If the piece with the tenon was bone dry and the piece with the mortice green, the green piece would shrink around the tenon as it dried and the piece with the tenon would expand . But no one is going to use timber half of which is dry and half of which is green - so how does this work?

This dry tenon wet mortice is used in Windsor chair making to great effect but on very small joints.

We live if a old Oak/Elm barn conversion which I project managed whist being renovated. Some talented Oak framer did the main work of joint reconstruction including using PU glue if on a few structural repairs. Draw bore tenons were used on almost every joint but looking at them now 5 years on all the joints have shrunk.
If the joints weren't massive and under load I am sure that if you removed the Oak dowels the whole thing could be dismantled apart from twist forces.
I am also interested to understand what I have missed in this form of construction?

 

[deema]

Great I for everyone, it's appreciated.

The cascomite was from powder. The gate was framed with panels, and a scooped top rail. I joined the panels together using grooves which I fitted with WBP ply acting as a tennon between the two pieces. None of the ply joints failed and were as strong as the day I did them. The oak was air dried, and since it was above 20% I have called it green oak! which is probably not the most accurate description.

What really amazed me was that the joint to ply was OK, however the tenons were fox wedged and the long grain to long grain glue joints holding the edges in had also completely failed. The wedges simply dropped out allowing the tenons to be taken apart.

The joints had not shrunk tight, in fact they had become looser than when first made. The mortice had expanded and the tennon had shrunk.