Gluing Endgrain - a question

[Zeddedhed]

On the understanding that you can't achieve a worthwhile bond on end grain, would it be right to think that if making a straightforward biscuited Butt Joint the glue should only be applied to the biscuit slots and not to the actual pieces being joined?

 

[Silas Gull]

If the end-grain is well sealed and sanded flat, I don't see how you can lose by gluing it.

 

[CHJ]

On the understanding that you can't achieve a worthwhile bond on end grain

Good job I did not know that, I would have wasted my time with all the stuff I've segmented. :shock:

If the end-grain is well sealed and sanded flat, I don't see how you can lose by gluing it.

I personally would not seal or go for a fine finish on any endgrain using conventional wood glues, you need maximum penetration of the substrate, I find clean sawn surfaces ideal for best endgrain bond.

 

[Zeddedhed]

"End grain will not glue, leaving endgrain surfaces glue free will save glue and make your joinery neater with no loss of strength."

this is on Workshop Heavens site here: http://www.workshopheaven.com/tools/Elm ... ml#SID=168

 

[Graham Orm]

End grain will glue, and the finer it's sanded the closer it comes to a side grain finish (in my opinion) therefore giving a smooth flat surface for the glue. A glued end grain joint may not be any use in a structural situation, but it will glue and stay if done with care.

Charlie, you have more experience than I on this I think, and I know that the general consensus is that it's a no-no. But surely the spikey uneven surface of freshly sawn end grain is the cause of the problem? It gives no continuous surface for the opposing surface to locate to. If it were possible to measure the actual glueable surface area of end grain it would be a tiny fraction of the overall area. Therefore I would think if sanded down through the grits to a smooth finish it can be glued just as well as side grain? No??

 

[CHJ]

Most wood adhesives require a Key to grip onto, my experience has been that a sawn endgrain surface (80t blade) provides a better bond than a fine sanded* or worse still a sealed endgrain surface. (yes I have deliberately broken test joints to try and avoid failures post assembly)

Extreme example, Cascamite or PVA won't bond to a plastic yoghurt pot, no pores or rough texture for the adhesive to grip.


*maybe fine dust is embedding in whatever small pores may be available for adhesive penetration.


Trying to ensure an endgrain/crossgrain joint won't fail due to wood movement causing wood structure or adhesive failure is another matter altogether in normal cabinet work.

 

[RobinBHM]

A sharp saw blade will cleanly cut across wood fibres and I think probably the best surface for gluing.

If a butt or scribe joint is broken, often there are plenty of wood fibres that remain stuck on the end grain side, which would indicate to me there is significant adhesion. Since there is no disadvantage from gluing the end grain of biscuited joint, I think it makes sense to do so if it can add to the strength. In reality, if the biscuit hole has glue squirted in it, this will squelsh out as the biscuit is knocked in any way.

When I glue up, I always apply glue to the end grain, although keep it away from the face by a few mm to minimise glue squeeze out.

If gluing up external joinery then the glue should be applied to the end grain since it helps to seal it as well as gluing.

As per the post above, adhesion to end grain is different to wood movement. There is nothing that will prevent wood expanding and contracting. A bottom rail of an external door for example can often be seen proud of the bottom of the stiles because the door rail has expanded.

 

[Phil Pascoe]

Robin - or anyone else come to that - any idea why the instructions on many adhesives say "apply to one side only"? I've never seen any reason for this?

 

[RobinBHM]

I think it is only to separate such glues from those that require separate application such as contact glues or uf glue with hardener that could have glue on one face and hardener on the other.

Quite often brushing glue on both faces is better as it both parts are wetted and coverage is likely to be maximised. I would always prefer to glue both mortice and tenon, as the action of assembly can scrape the glue off one side of the joint.

 

[Zeddedhed]

So it would seem that I have ben misinformed.
I have to be honest my opinion is based purely on what I've read or heard from others. I've never performed any kind of test.

Normally when I glue up anything I spread the glue with gay abandon and it ends up everywhere. I shall continue with gluing end grain for now until I have cause to think again.

Thanks guys.

 

[John15]

I subscribe to Rob Cosman's Hand Tools tutorials and on a number of occasions he's said he is adamant that there is little strength in glueing end-grain. I have no experience one way or the other but it seems that expert opinions differ.

John

 

[Phil Pascoe]

Strangely enough, I've a bottle of PVA in front of me that's instructions say "apply a thin bead of adhesive to one surface" - I would have thought that was inviting a "dry" joint. I'd sooner swamp everything and wipe the excess off. In a stressed situation I would fill all gaps, as (to my mind, at least) the less gaps the less the chance of any movement.

 

[geordie]

there is a article on the woodworkers forum about this that would be worth a read backed up by tests

 

[Silas Gull]

Certainly an interesting thread. Maybe the key point here is that there is a biscuit involved. In anyone's book this is a loose tendon which, if glued correctly will hold the joint together. I have made several notice boards that feature doweled butt joints - some of which are now more than a decade old and still holding well.
Others are made with keyed mitre joints, which is still really an endgrain joint, albeit at 45 degrees, and crucially, with an additional element to pull the thing together.
I don't see a problem with gluing end-grain in the right context.

 

[custard]

Depends on the glue. PVA will give the superficial impression, on an end grain joint, that it's providing some adhesive strength, but once the timber moves it'll soon separate. Use epoxy however and end grain gluing will genuinely add to the joint's strength.

 

[Zeddedhed]

What Epoxy would you recommend? Are there any one part epoxy glues (or am I being dumb)?

 

[GLFaria]

there is a article on the woodworkers forum about this that would be worth a read backed up by tests

Hi

would you mind posting a link? Thanks.

G.

 

[JohnPW]

Here's an article with tests:
https://www.woodworkersinstitute.com/page.asp?p=4114

 

[GLFaria]

Here's an article with tests:
https://www.woodworkersinstitute.com/page.asp?p=4114

Thank you very much

G.

 

[CHJ]

Here's an article with tests:
https://www.woodworkersinstitute.com/page.asp?p=4114

Thanks for the link, very much my experience working with simple segmented pieces, the emphasis on the point about adhesive being able to penetrate the end fibres as a key being as per my findings, that a clean sawn surface leaves an open pored surface not blocked by dust or abrasive particles.

This image from that link says it all, and matches my experience if I've glued up wood with too high a moisture content, when it dries out the mechanically restrained joints fail more often by side grain separation than end grain failure.

The Oak in this failure is effectively end grain bonded at the point of wood failure.