To Trust Or Reinforce?

33

Edge Jointing Long Boards For a Table Top

How confident do you feel trusting glue for edge joints?

In traditional woodworking most of the glue bonds we do will have some mechanical strength, and a well cut joint will hold together without any glue at all – it’s just there as a bonus.

But when we’re edge jointing long boards, such as when we glue up a wide panel or top, it can be an exception. For these joints we’ll often look to the glue alone to hold the two pieces of wood together.

Glue is one of those miracles, like sending an email, that does its job without leaving any hint of how it happens. For my simple woodworking mind, that disturbs me.

For small glue ups, like on our side table’s top, I’m happy to appreciate this miracle.

But as the joint gets longer and thicker, I start to lose trust.

For these joints, I always like to add reinforcement for peace of mind.
There’s several ways to do this, and on a table I’m building this week I’ve opted for loose tenons, draw bored in to each section of the top. This physically holds the two pieces together, so I can see how it works, and that makes me happy.

Loose tenons add extra strength when edge jointing long boards

With the modern wood glues that we have available this may seem like over kill.
Modern glues have exceptional strength and there’s a lot of work in adding these extra tenons. I posted a picture of my reinforced top on social media, and a good friend brought up this exact point – that my joints are outdated due to modern glues.

I was going to explain myself in a comment back, but it got very rambly, so I decided to write this post instead.

‘Glue That’s Stronger Than The Wood Itself.’

Modern glues will often say they are ‘stronger than the wood itself’, but I have two problems with this.

Firstly, strength is important, but when we build furniture we’re not normally looking for the strength to withstand an attacking Northern Yob. Instead we want a balance between strength and flexibility. I look for methods that hold wood together in a manner that sympathises with the nature of the wood, its elasticity and it’s will to move.
That’s why joints are so important in woodworking, we don’t simply stick the end grain of an apron on to the side of a leg with super glue, we use a mortice and tenon.
I don’t consider it over kill to take the same approach when edge jointing long boards, in fact I find it quite strange that it’s so uncommon to take this approach today.

Concealed loose tenon within an edge joint

These loose tenons will not ensure that the glue line remains invisible for ever more, but if that glue line should open up I can be sure the top will stay firmly together, whilst allowing enough give for the timber’s seasonal movement.

The second problem I have with putting all my faith in a glue is consistency of application.

Good glue lines are unlikely to have a weakness that would lead to a crack or failure, but it’s difficult to be assured that they’re good.

Building workbenches for a living gave me more reason to develop an obsession with glue lines than most. And it really did become an obsession (ask Helen).
To create a level of consistency and stability within our benches we took the modern approach of creating the tops with face to face laminations. This is more problematic than edge jointing, and it troubled my mind to simply trust the glue, so the early days of development were filled with research and glue experiments.
At first this just confirmed my worries, as seemingly consistent test glue ups gave completely varied results when attacked by hammer and chisel. Good joints would not give no matter what. Bad joints plopped themselves apart with a mere touch.

The reason for this is because gluing is very scientific. It’s affected by humidity and temperature, the level of surface prep, and whether you’ve applied too little or too much clamping force.
We learnt that some glues will not be able to reach their stated strength if there’s any more than 2% difference in the moisture content between the pieces of wood being joined.
This is usually easy to avoid using kiln dried timbers, but large sections can have more variation than that just within themselves.

We developed our system to perfection, with an exhaustive process of precautions and steps for the environment, the timber, the glue, and the surface. Then we added reinforcing tongues between each join.

That all became very scientific, but now I’ve gone back to building furniture and want to leave my glue-line obsession behind.

A Quick Word On The Hazards.

A big part of hand tool woodworking for me is being in control of the pace, the details and the processes. This is helped by not having to wear goggles or ear muffs, let alone a hazmat suite for chemical protection.
Health and safety is bloody boring, but some of the more sophisticated glues are pretty nasty, and not just whilst applying them, cleaning up and sanding can expose the toxins.
If you do your tarting up with a beautiful Festool (or such), orbital sander, complete with dust collection, then you’re going to have a mask on anyway. But a sweaty half hour of deep breathing as you flatten your top with a hand plane, and you’re going to find a fair old bit of that in your lung. And some very strong glues will easily damage your plane iron too, and this shows in your finish.
The suitability really depends on application, and approach.

So yes, modern glues are great.
But I’ll stick with the glues that are simple to apply and are considered non-toxic. For the likes of large edge jointing I’ll keep my trust in reinforcements I can see.

I accept that I probably am out dated, but then we are all here to talk about hand tools…

This isn’t a post to scaremonger you against simple glue lines. There’s some world-class furniture out there that’s held together with the stuff.
It all depends on your application, and since my methods are traditional, I find it suits best to stick with what’s always worked; just as you wouldn’t introduce concrete to a mud and stud home.

If you are feeling dubious about your glue lines when edge jointing long boards, just think of the extra practise you’ll get chopping out for these loose tenons. Or for the faster approach, have a look at the ‘planked top’ construction which depends on the simple flexibility of the humble nail.

33 Responses

  1. Michael A. King

    Very insightful, thank you Richard. I had always wondered about the ‘stronger that the wood itself’ claim, and what that really meant. I would also like to point out that the use of such joinery as you have displayed in this article seems to me to give the piece more visual interest.

    Thanks again for sharing your talent.

    Michael

    Reply
  2. David R

    Anyone else seeing the tiny man sticking out of the edge with its peg hands locked? 🙂

    Richard, have you any experience with using sliding dovetails to reinforce table tops? It’s supposed to have been a fairly common occurrence for furniture here in Germany (called Gratnut). There’s a nice video series on that topic here: https://www.youtube.com/watch?v=SgHxHeKeG7E

    I think this is a nice option for table tops or shelves.

    Reply
    • Richard Maguire

      Hi David,
      Thanks for the link, very interesting – wish I could understand, but visually I got the gist.
      I’ve done sliding dovetails a fair bit in place of housing in things like shelves for a cupboard and also for stool seats. It certainly seems to be very European. This is incredibly useful on thinner material where it also stops the cupping, although I haven’t attempted it on any table tops or anything wider – though you’ve got me itching to give it a go.

      Reply
    • John

      Hi David just had a quick look at that link……totally amazing but can’t understand
      German ……stupid me!!
      I am able to follow when he demonstrates and, to a degree when he talks

      Amazing tool……..it’s all down to time..time ..time. I would love to make that dovetails plane…..I have the word and new iron I can grind.

      Thanks John

      Reply
      • Momist

        David, even without any German (I’m hopeless), you should watch the follow up video as well, showing the installation of sliding dovetail bearers in a replacement table top. In that, he shows us that you don’t necessarily need the special saw with the angled sole, fence and depth adjustable blade. He uses it for one side, and then uses a Japanese type pull saw for the other side. On both, he uses an angled guide bar made from hardwood.

        Yes, the special shoulder plane intrigued me as well. I have two skew bladed wooden shoulder planes as well as an adjustable metal one, so I am pondering on adapting one of the wooden ones. But then, I’ve never felt the need for sliding dovetails yet, although I could have used them on my own dining table. I used battens with screws in slots.

        Reply
    • Richard C

      Hi David,
      “Anyone else seeing the tiny man sticking out of the edge with its peg hands locked?” – Not till you mentioned it. Must be one of those “Northern Yob” types who has been put in the stocks as punishment for smashing up the joint!

      Reply
    • Chip

      Wonderful way to attach a cleat to a table top. Would suggest using quarter or at least rift sawn stock for the cleat. You can create a shoulder on the cleat or just maintain the dovetail angle (suggest 14 degree for maximum strength) over the entire width of the surface. Far superior to breadboard ends or screwed on cleats.

      Reply
  3. Jasper

    Hi Helen,
    Please tell us more about this obsession. How severe can it be?

    One thing I learned when restoring double basses (but also tables), is that cracked (hide) glue joints are easier to repair when they can be opened and accessed.

    Your beautiful tenon would be very much in the way, especially when restoring “ethically”, where all original material should be preserved. Not only the making takes more time, repairing too.

    But indeed you can be assured that it won’t fall apart without warning.
    And I too use butterfly inlay joints to cross cracks and prevent further splitting.
    Or biscuits to make lining up boards easy.

    Reply
  4. Joe

    When I make something, I’m not only thinking of next 10-20 years, I’m trying to think what will it be like in 200+ years. Adding a few pins, etc helps increase the odds it will go much longer into the future before some craftsman of that time needs to restore it (and may appreciate what I have done to try and increase the lifespan between restorations).

    Reply
  5. Chris Buckingham

    I , like you, really want to use a mechanical joint even on a board joint, although modern glues are said to be good, and to a point can be proven to be good, in years to come they could fail, in any case the kind of jointing I do on a table top looks much better showing pegs or a double dovetail , it becomes a feature, I even resort t a tongue inserted the length of the board for an Oak door. One thought I will leave you with, and that is way back in 1914 aeroplane propellers were laminated up and glued only, no mechanical fixings used, and they had to pull an aeroplane through the sky, they were however meticulously jointed between the laminations, but it was still a glue joint. But I still prefer a mechanical joint, I suppose I just do not trust modern glues!

    Reply
    • Richard Maguire

      Absolutely agree with you on the features that a reinforcement can add.
      Time and wood movement / stresses seem to be the biggest killer of glue joints.

      Reply
      • John

        Richard can I just say that I had they privilege of walking through the “forbidden city” in China ……….no glue there just good joints and pegs……..all built off wood foundation on swamp land…I’m told……..amazing

        New to your blog and love the quick interaction from other followers

        Thank you…. John

        Reply
  6. John

    Richard ….amazing coincidence I have been going on about glue lines and associated glue problem when I read your blog

    I had a piece of matured oak ( ex skip and I did ask owner) 15″ X 72 ” x3/4″ great for my daughters shelf…….but she wanted edge thicker. I cut a strip off the back and glued to front…..after throughly preparing mating faces.
    Using a good quantity of resin W ( evo stik manufacturer, in dark blue container)
    Shelf 72″ long with now 40mm front edge glued held with 15 clamps!!!!

    When dry plained off and bingo light grey glue line ……now I find that water effects oak so when using damp rag to clean off I caused glue line??

    Reply
    • Momist

      John, I think the dark blue container type is “waterproof”, meaning useful for outdoor type joinery where a visible glue line is the least of your worries. I have been a long-time user of the ‘white glue’ variety of Resin W in the dark green container, and have never had a problem of visible glue lines. However, I can’t speak for glueing oak, as I rarely have the opportunity to use that wonderful wood, and when I do I used traditional joints where the glue wouldn’t show anyway.

      Reply
      • Richard Maguire

        Hi John,
        A visual glue joint isn’t necessarily cause for concern with regards to strength, it may be expected for a particular type of glue, and you won’t have caused any damage by wiping away the excess with a damp rag – particularly since it does sound, as Momist said, that this glue is waterproof.

        Reply
      • John

        Hi Momist….thank you for your interesting comments. I have always used the blue
        exterior resin W for interior and exterior, never seeing the point in having green interior

        Very interesting to read of your use of green for interior work.

        My shelf was for a kitchen, so inside and I was expecting a glue less face when planed square

        Both green and blue are, as you know, water based and need wiping off with damp rag.
        My problem is that oak is effected by moisture and parts of the grain ( I’m told of the correct term but can’t remember?) will turn black.

        I made a little box from scrap oak skirting……again using Resin W ( blue container) when wiping off a small amount of glue from joint, it turned black……I was gutted.

        Anyway thank you and others together with Richard for interest in my question.

        John

        Reply
        • Momist

          Hi John. I always thought that the black stain on (in) oak was caused by the presence of iron. This is why steel screws will turn the wood black around them over time, as the oak reacts to the iron in the steel using the natural water content (even at <12%). I have used brass screws in the past for this reason (also, that was on a boat where steel is never a good idea). Maybe the waterproof version of PVA has some iron content that is staining the oak? The only way to prove that would be a test piece using the same or similar wood and the green container glue. It's only a fiver for the small bottle (around here) and I gave up buying large bottles as it tends to work better when not so old.

          Reply
          • John

            Hi Momist I think I have led the thinking here, up the wrong path?

            Whatever glue I could use ( and I will try a small green sample) it’s the damp rag that causes the problem I am sure?
            I made a collection of bathroom bits ….soap dispenser holder etc with simple
            housing joints…..no screws just good old Resin W …….all ok so far?? It was when I used a damp cloth to wipe of a very minimal amount of glue…..hey bingo dark stain …….so answer here is brass screws in housing joint.

            I used a water based varnish (me stupid boy) and it caused dark lines!! Had to plane off, end result ok

          • Momist

            Hey John, go one better and use sliding dovetail joints, secured with a single brass nail/pin. I have been so lucky to inherit a box of assorted size brass pins up to 1″. Does your water supply come through steel pipes? Or maybe there is iron in the water supply, which is harmless to us humans but the tannins in the oak would react to it.

  7. Christopher

    If you’re going to go traditional, you should be using hide glue anyhow. Which is totally benign, so no masks, no worries about breathing in, no damage to plane irons, and anything older than 100 years has done just fine being held together by it. Anybody want to bet how Gorilla glue will be holding 200 years from now??

    Reply
  8. Blaz Grapar

    I was also thinking sliding dovetail edge joint or loose sliding dovetail. Breadboard ends, butterflies etc. They will all pull edges together mechanicaly.

    Reply
    • Richard Maguire

      Hi Blaz, absolutely, the reinforcement can also be chosen by the application. For example breadboard ends are also useful for minimising cupping in thinner boards, and butterflies will add to the aesthetic and may or may not suit the style of the piece.
      I’ve got a nice slab of waney edge oak with a split that’s just screaming for a nice butterfly.

      Reply
  9. Momist

    Richard, for many years now I’ve been using the Evo Resin W white glue out of preference, and lack of experience with any other glue. You wonder about the claims of ‘stronger than the wood itself’? Well, a long time ago, gluing common construction timber (a.k.a. ‘redwood’) (i.e. pine) I made the foolhardy error of gluing the wrong two pieces together, They had only been together about ten minutes when I realised my mistake, and I forced them apart again. This was a halving joint, so no end grain involved. Taking the joint apart just split both pieces at the weakest points of their grain tearing chunks out of each half, resulting in ragged halves. The glue hadn’t even dried! I have trusted the face to face properties of this glue ever since. Prior to that I would use a loose tongue for edge joints where I doubted the strength of a glued joint. I no longer bother with that.
    Of course, I don’t know if 200 years down the line it will still hold together, nor can I speak about any other wood type. I have successfully once used it on teak though, and had no problems.

    Reply
    • Richard Maguire

      Hi Momist, the small side table that we recently built is joined with unreinforced bridle joints and an unreinforced glued edge joint in the top, and I thoroughly trust that this will all stay together. It’s only when things get much larger and more structural that I start to loose faith a little as there’s a lot more stresses and continual wood movement involved, which over many years is going to take it’s toll.
      I sympathise with your experience, I’ve been there many times where you realise you’ve made the mistake a few minutes after the glue’s grabbed.

      Reply
  10. Gavin Rondeau

    I’d just like to say that the pegs LOOK really good.
    I think the aesthetic argument is one that should carry some weight.

    Reply
  11. Bob Barnett

    Your tendons are cross grain to the boards. Does that concern you? Have you tried placing the tendons with parallel grain. I love the way the finish boards look where the joint is part of the design and not hidden.

    Reply
  12. Richard C

    Hi Richard M,
    I’m of the same mind on this. I’m currently building a small workbench using 3×2 whitewood (probably spruce) for the top, laid thin edge to thin edge with cross grain “loose” (but glued) tenons at intervals along the length. I’m not so much worried about the glue failing – the tenons are more to help prevent the wood shearing either side of the glued joints. I’m not sure if this is a valid concern, as it’s only a short top – and especially as chopping the mortises was hard work, despite being good practice!
    All the best and thanks for your blogs – glad to see you’ve started up again after a break.
    – Richard C

    Reply
  13. Ronald Carl Dennis

    Consider this. If my good name is going on a piece of work, I do not wish to see it again because of shoddy workmanship. Work done twice is a loss of time and reputation.

    Any reasonable precaution in design and construction should be cheap insurance of both my time AND reputation.

    Reply
  14. Brian Hackett

    I’ve never liked the term “stronger than wood”. It implies that if the piece will fail, it will be a structural failure randomly throughout the piece, that the joined piece is just as strong as a single, solid piece. I haven’t done extensive testing (or any at all for that matter!) myself, but I’ve seen some videos. It appears that the failure is always next to the joint. It’s my opinion that area directly on both sides of the joint is weak because the layers of wood are incomplete. A straight cut through wavy grain leaves incomplete segments that were once a single layer (don’t know if I’m using the correct terminology or explaining this effectively). Therefore the fact that the glue IS stronger than the wood (and inflexible, as you said) puts extra pressure on an already weakened area. But I’m relatively new to woodworking, so I could be wrong. I haven’t seen anything to back this theory up. What do you think?

    Reply
  15. Gav

    Hi Richard,

    It is fairly common to see glulam structural sections in an exterior environment in Perth where I live. The biggest failure I see is that the timber usually doesn’t handle the strength of the glue which is graded for such use. On one vertical jarrah post the timber separated next to the glue lines in more than one place. The glue held fine, at the time, we have very strong uv which breaks down seemingly almost anything, but it didn’t have anywhere the apparent flexibility required to account for the timber movement with the seasons. External finishes failing or not being applied, or reapplied, properly can be a contributing factor but it does make you wonder somewhat for long term durability. Creeping glue lines can be a drag but I would rather in some instances that movement is allowed for.

    Reply
  16. Meikel

    A question regarding the aesthetics: Since pegs or butterflies will be seen, how do you go about eg. symmetry of the location of the joint? A row of butterflies or pegs running along the center of a board might add to the design of the piece. But shifted to one side….

    Do you add fake ones to restore symmetry? Or make them semi visible by putting them on the underside of the table?

    Reply
  17. Brandon

    I would really like to know if anyone has experience of fixing down a planked top with pegs instead of nails.
    I am sure it can be done – just wish to know of any precautions to take, or peg dimensions to use.

    Reply

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