Joining two timber

[Pauls321]

Hi all,

I recently made a project wherein I joined/laminated two timbers together. The timbers being Blackbean and Silver Ash. I used Titebond Premium 111 and clamped the project for two days. Following all this I finished the timber to a beautiful smooth finish, right through to 2000 grit sandpaper on my Triton ROS.

The finish was lovely, I then used Tru Oil for the main finish. 10 coats of it. Lovely finish.

However within a couple of months I could feel the joint/s in the timber. Run my fingers over them and a small jointline could be felt.

Any thoughts on this?. Could the glue have expanded slightly?. I am positive the timbers have not shifted at all.

I am curious as I am starting two more similar projects and don't really want this to happen again.

Paul

[elanjacobs]

Titebond is PVA, PVA is a thermoplastic and will always have the potential to move with environmental changes.

If you want to avoid it, you need to either use polyurethane or epoxy, which set chemically.

[Pauls321]

Hi and thanks for your reply Elan,

Are you saying that the titebond glue has the potential to move but not the timber. The joint itself feels fine and very strong. I just feels like a tiny smidgeon of the glue has oozed out after a couple of months and makes you "feel" the joint. Long after it was sanded and finished.

Very interesting

Paul

[John.G]

Silver Ash is quite stable, Black Bean is stable once dry but prone to collapse and variable shrinkage until at EMC to core. If I were looking for a culprit in that mix that would be the most likely place.

[Kuffy]

Of the three titebond pva glues, titebond 3 creeps the most. After the glue has crept out of the joints as it has here, you can sand it back. Although the glue continues to creep throughout the duration of the pieces life, it should no longer creep out of the joint. The problem now is the glue line will be slightly sunken to the surface of the timber, so it is a very bad choice of glue if you wish to have high gloss finish. But for a satin open grained finish, you can barely tell.

[Mobyturns]

That is half the battle, understanding how timber reacts to constantly changing environmental conditions and specific changes such as glue ups. I like to let the stock acclimatize to my workshop before processing, then any of my laminations rest for weeks even months before I proceed to turn and finish them. This allows the EMC to stabilize through the whole piece, and not have "localized hot spots" of high EMC near joints.

From experience, in laminations with boards / strips of different width but the same thickness some species seem to "hog" the moisture from PVA glues so the movement is far more pronounced in that board / strip than in its neighbour which may be comparatively starved of moisture.

Timber swells with moisture, or any thing that fills the vascular structures in the wood. Sawn timber also swells at different rates relative to how it was cut (flat sawn etc) - different radial & tangential shrinkage / swelling. You risk differential shrinkage if you finish it before it stabilizes fully. Glue creep, or stepping at a joint, are also well known phenomena, controlling them is another issue which is not so well understood.

Many wood workers assume that the shrinkage / swelling will be the same for the same species and even different species when laminated together. This is not true, and can even be observed in small pieces as "step" for want of a better term. The boards even though thicknessed at the same time to the same dimensions may now be different thicknesses (dimension) due to changes in environmental conditions since processing, so a "step" at the glue joint may be felt that is not glue creep but is due to differential shrinkage / swelling. It is truly amazing how sensitive our tactile senses are.

These are a brief summary of some fairly well controlled research (by others) on glue creep.

Water soluble adhesives tend to be more prone to creep, particularly when exposed to extreme moisture and temperature.

Glue-ups with boards containing opposing grain direction (flat sawn -to-quarter sawn) produced a stepping effect based on the tangential (opposing) wood movement.

[Bob38S]

I would ask, were both sides ie top bottom finished the same?

The potential for movement, in most cases, is greater if the underside or non seen parts are left unfinished. It may save some material, a little time, but in the long run it minimises movement problems. The underside and unseen bits don’t have to be finished to the same degree as the main bits but they do need to be sealed.

[elanjacobs]

Hi and thanks for your reply Elan,

Are you saying that the titebond glue has the potential to move but not the timber. The joint itself feels fine and very strong. I just feels like a tiny smidgeon of the glue has oozed out after a couple of months and makes you "feel" the joint. Long after it was sanded and finished.

Very interesting

Paul
Timber will move no matter what glue or finish you use, but a raised glueline is due to the glue itself.

[IanW]

It's not clear to me from your description that glue-creep is the culprit, but that should be easy enough to establish by careful inspection, there will be a small 'mound' along the joins. If you have distinct steps of wood at the joins, then differential wood movement is more likely.

If glue-creep is the source of the problem, then it might respond well to re-finishing, particularly if you wait & let it go through the annual moisture-cycle. PVAs do harden a bit over time (at least the brands I've used do), though always remain a bit plastic, especially at high temperatures, but as long as the woods settle a bit & don't put excessive pressure on the joint lines, there's a good chance your joins will remain flat into the future.

If differential wood movement is responsible, things get a lot more difficult to predict - it's always risky when mixing species as you've done, unless you know the woods you've selected are usually compatible. Silver Ash has double the moisture-movement coefficient of BB (Ash 3.5% radial 6% tangential vs BB 1.5% & 3.5% respectively), so if you weren't too fussy with grain orientation and have tangential Ash meeting radial Bean, there's always going to be a conflict at those points. It may settle, or at least the differential movement with the annual moisture cycle may reduce to negligible proportions, or it may not. My own (limited) experience with Silver Ash is that it's a fairly 'lively' wood initially, but settles over time.

My suggestion would be to wait for at least a few months & then re-finish. That's the easiest way, & has a reasonable chance of solving or at least greatly reducing the problem, whatever its source....

Cheers,

[rustynail]

When using oil finishes and PVA glue I have found this ridging effect to be quite common, particularly with laminated rifle stocks. To overcome the problem, I oil the glue lines on the stock first, before final sanding, leave for a few days to allow the oil to penetrate and harden and then do the final sand prior to the overall oil finish. By doing this, the ridging doesn't seem to return. Hope this helps.

[Pauls321]

Thanks everyone for giving me very valuable input into this issue. The culprit item is a through neck guitar which I made a few months ago. Using the BlackBean and Silver Ash. Why I am now becoming concerned is that I am in the final stages of building another two through neck guitars, this time using Purple Heart and Hornbeam, similarly laminated.

I am getting very close to final sanding stages, and also used the same Titebond 111 Ultimate. Funny thing is,, if you look at the site for StewMac, the worlds largest luthier accessory selling site, what is the brand of glue they recommend,...........................Titebond 111 Ultimate, (the best in the world).

On the previous build I used Tru Oil for the finish, this time I am going to use Wipe On Poly.

So I am taking all your comments into my head, thanks again everyone.

Paul (Ps the pics of the guitars I mentioned are in the Musical Section of this forum)