Glue ... what glue do I use

[woodpig]

Do you know if Cascamite has a shelf life Chas?

 

[Keithie]

I've not been here long and have heard the term 'creep' used in connection with PVA a few times. My grandfather always told me to put a bit of grit (eg fine sand) in glue to stop it moving and I think I read someone on here mentioning that too.

I've not figured out what is meant by 'creep' in PVA unless its that the joint moves before the glue has properly cured.

It seems to me that if pva binds tighter than the strength of (all?) wood fibre then surely the concept of 'creep' is eirher redundant or a function of 'useless user' syndrome (I know a fair bit about being a useless user!).

The explanation about differential expansion of endgrain vs side grain (or, I guess, different woods with differing permeability) is the best I've heard yet...but still, to me, falls into 'user error'.

Is there a well defined meaning for 'creep' as it relates to wood glueing ... I just assumed it was to do with the two pieces sliding a bit when clamped together...but maybe thats not correct?

 

[Phil Pascoe]

No, it's long after that when one piece moves at a different rate to the other. Some glues are better at preventing it than others. Nothing to do with assembly problems, irritating as they are. Sand? I'd not actually heard that one . Why not?

 

[Phil Pascoe]

The shelf life of glues crops up regularly, I suspect manufacturers are averse to allowing very much as they cannot guarantee storage conditions. I see on my new D4 they say between 10c and 25c and 6 months from manufacture. I'm sure I've bought the stuff older than that. I threw the old one out as it had thickened, but it had never frozen and wasn't very old. I don't use it for the ends of blanks as it is totally waterproof, which would defeat the point I believe. I suspect the temperatures and times are getting more and more critical. Cascamite - Resintite is the Everbuild one - there are probably loads similar should be decanted into smaller containers upon opening. I forget what the label says offhand. I believe if humidity is kept from it it will last for ages, and also that it shows quite quickly and obviously when it deteriorates. For most of us putting stuff into smaller containers whether it's oils, varnishes, glues, no matter what, makes sense - we do not use stuff fast enough.

 

[CHJ]

Do you know if Cascamite has a shelf life Chas?

The main problem with Cascamite powder is the fact that it uses water to activate and the normal room atmosphere contains enough humidity to start the activation.

It is wise to limit your purchase bulk to match your expected using time.

I take the precaution of decanting any larger purchase (balancing retail cost against quantity) into smaller sealed pots or zip bags so that air exposure is limited.

If it has started to deteriorated it soon shows in a gritty consistency when mixed rather than a smooth cream.

 

[CHJ]

.....I've not figured out what is meant by 'creep' in PVA unless its that the joint moves before the glue has properly cured.
......

When I personally refer to creep I mean joint movement between two adjacent pieces of wood, the only PVA's I have used do not set to brittle hardness and allow minute movements of the adjacent pieces of wood to move relative to each other without the adhesive letting go of the wood bond. I'm talking about being able to 'feel' the joint if running a finger across it, not a visual deformity.

The risk you take in using something like cascamite with opposing wood grain orientation is that end grain joint may let go as a whole or in part or the wood split or a combination of both dependant upon grain juxtaposition, I've had examples of both.

The fact that PVA's behave this way is recognised by various manufacturers when they advertise their products as having minimal or reduced creep.

 

[woodpig]

I'm talking about being able to 'feel' the joint if running a finger across it, not a visual deformity.

This is exactly what I've experienced and particularly noticeable on a turned piece.

 

[andersonec]

When I personally refer to creep I mean joint movement between two adjacent pieces of wood, the only PVA's I have used do not set to brittle hardness and allow minute movements of the adjacent pieces of wood to move relative to each other without the adhesive letting go of the wood bond. I'm talking about being able to 'feel' the joint if running a finger across it, not a visual deformity.

.

Another reason a slight ridge can sometimes be felt is that one piece of wood is softer than the other so that when sanded the softer timber is sanded away quicker resulting in a slight ridge at the joint. After finishing and oiling my end grain chopping boards they are left for a week or so and sure enough they develop a "ridge" at the glue line, I use a scraper to remove this and it does not come back.

I think D3 PVA is quite sufficiently strong enough to do most jobs, any stronger or more waterproofing requirements then D4 is the next step, I do not think we have to pay high prices for glues to be shipped across the Atlantic.

I use D3 for every day stuff and D4 for my chopping boards which may get immersed in water.

Andy

Andy