If you are a wood worker like me you will eventually come to a situation where end grain will need to be joined somewhere and the concern about glue joint integrity fills the mind. Is the joint strong and can it be trusted? End grain has it’s own set of peculiarities that we need to contend with if the joint cannot be avoided. But the first question is this.
Can End grain can be glued successfully? Yes it can be but consideration should be given to the list below. How you approach this process will determine your success.
- The moisture content of the wood is important.
- Glue selection is a consideration.
- The wood joint location within a project is vital.
- The mill profile of the wood pieces should match if possible.
That is the short answer and it really has no meat to it. Woodworkers generally look to have their projects last for many years, and to use end grain gluing within a project demands some knowledge of how wood reacts and behaves when glue is applied.
If you wish to gain a better understanding of what is meant above, read on.
The moisture content of the wood is important.
Sometimes when hobbyists take up woodworking the rush to create something unknowingly sets the stage to overlook details that are pretty important for the entire time enjoying this wonderful hobby.
Moisture content of wood is one of those details when gluing end grain.
Moisture in wood is a curious thing because it is always changing. What was dry and stable one day can be a little less dry and be quite unstable the next and this is most often caused by climatic conditions changing faster than is a typical seasonal drift of wet to dry air and back again.
We as woodworkers can understand the slower seasonal changes easily, and have been doing this since forever but when sudden changes in relative humidity happen the effect on dry wood can be truly astounding. A dry board resting on a bench top will cup overnight. Doors jam in their openings. Things made of wood move.
It is with this knowledge that we look at glue joints and end grain glue joints in particular. For the beginner woodworker it might seem a simple task to just cut some wood pieces and spread a little glue on them, clamp it up, and away we go however the experienced woodworker knows that it is never that simple.
Moisture levels cause wood to move. Plan for it.
Glue selection for gluing end grain is a big consideration.
If details on end grain glue joints were rated on a scale of 1-10, glue selection might be at the top of the list. While we discuss this section on glue selection just keep the section above on moisture content in the back of your mind because that section applies throughout this article and will affect everything in your woodworking hobby life.
Glue is the woodworkers’ oxygen. We don’t survive for long without it. It holds our carefully shaped and sanded wood components together and is expected to do what we ask for many years and yet be almost invisible.
We place a lot of faith in this stuff, so it makes sense to think about which glue to apply to a particular application.
Not all glues behave the same way and the requirements that any glue may demand to perform satisfactorily could also be the worst situation for another type of glue.
A lot of the difficulties revolve around moisture. Check or know the moisture content of your wood when it is stable and use a glue that is appropriate to that moisture profile.
When we glue end grain we add an extra layer of complexity to an already crowded field of challenges. Here we start to move into the behavior of end grain and we leave the glue specific side of things for a moment; still considering the information that is relevant to glue selection, that being the glues viscosity when applied and the glues stiffness when cured.
End grain is a challenge because it has attributes that can benefit some projects but create difficulties in others. This is because end grain is the open face of what can be described as a bunch of straws packed together tightly. As you apply a liquid to this open face, in our case glue, this liquid is drawn into the internal cavities that make up the grain.
Surface tension and capillary action play a part in moving the liquid from the surface into the wood and the density of each wood will dictate just how much liquid penetrates and how quickly it happens.
The challenge for the woodworker is to gauge this amount when gluing end grain because the result of not understanding and compensating for this behavior will deliver a glue-starved joint.
The experienced woodworker will apply glue several times to the open face before the final squirt is delivered and the joint faces are closed and clamped together.
Apply glue to open faces of end grain several times. Watch for glue to remain on the surface before clamping.
The wood joint location within a project can play a large part.
End grain gluing is not a stand-alone practice in woodworking. It is usually something that cannot be avoided while assembling other components that make up a particular project.
Often times we will use fasteners like screws or nails to hold the components together while the glue cures and forms the kind of bonds we rely on.
A good technique using just glue is to overlay other wood bridging across the end grain joint.
I will use a practise called segmented turning as an example. The process of segmented turning uses end grain gluing for much of the initial assembly work before the construction stages take place.
A typical turned item like a segmented bowl will have layers that are stacked one on top of another. These layers (rings) are made of individual pieces of wood that are glued together at the end grain. Each ring may be comprised of many segments and the integrity of every ring is completely reliant on the quality of the end grain glue joint.
This may lead you to think that end grain gluing is great because all of the segmented turner guys use it and look at what they do; this thought would be wrong if left as it is because the making of each ring is just a component of the whole project.
It is in the construction phase of the segmented bowl where the weaknesses of the end grain glue joint are eliminated.
To gain an understanding of strong construction look at a brick wall. Each joint is overlaid by a full brick in a stretcher or common bond layout. This gives strength to the brick wall and the pattern that each brick is placed within is the same pattern as the segmented bowl.
The segmented bowl is the same thing only in wood. The similarities end here because wood has two primary structures, being side grain and end grain and the brick has no grain. Side grain gluing gives the most strength and reliability because of the grain length and the non-porous nature of the grain orientation vs the porous nature of end grain.
A single application on a side grain joint with the appropriate glue is all that is usually required to achieve a good connection.
It is now where we can start to see the inherent weakness of the end grain glue joint. It can hold a joint together as a step within a projects construction, but is not a reliable joint in any way and should not be left as a stand-alone joint if any reasonable life is expected.
End grain gluing is a step within a process. It is not a stand-alone practice.
The mill profile of the wood pieces should match if possible.
This section touches on the entire article above. We know that moisture moves wood and we also know that different grain orientations will have different behaviors.
When it involves wood there are so many variables that it can become hard to make a decision on how to approach some part of a project. It is easy to overthink things.
To make this worse, let’s look at how a log is cut at the lumberyard. The stock you have on hand could be quarter sawn, rift sawn, or plain sawn.
This article is not big enough to cover all of these cut types in depth but what needs to be understood by the wood worker is that each of these cuts will cause your piece of wood to react to moisture in different ways, and these should be looked at before any project planning takes place, particularly when glue joints are concerned.
This is very important if the project is planned to be a family heirloom piece.
So finishing up, if you arrived on this article looking for information of end grain gluing and were wondering about the strength of the joint, I hope you found some useful thoughts on the practicalities of the glue joint.
The best advice I can give is don’t try to re-invent the wheel. Modern glues do have fantastic holding abilities but they cannot counteract the inherent behavior that end grain wood holds. That side of the deal is for the wood worker to make the neccesary allowances.
Don’t re-invent the wheel.
Here is a great article on gluing end grain in a real world situation. What is the best glue for segmented turning.