I’m wondering what the wisdom of experience has to say about the best glue for mortise & tenon joints in a chair. I’m new enough at this that some of the joints are, while snug, short on contact between the tenon and mortise due to my still-growing skills (the mortise walls aren’t as smooth as you’d like to see.) So, I was considering using a polyurethane glue, such as Gorilla glue, hoping that the expanding nature of the glue would fill in. The wood is pine, but this is just a practice run; I’ll be using quartersawn white oak eventually. Comments?
Thanks,
CharlieD
Replies
Try TightBond, rough surfaces are noe a real problem. If you try Gorrila glue make some test joints first to see how much it expand & oozes out. You have to be very careful with a important projest.
Good luck
Charlie, I don't think using a gap filling glue, like Gorilla Glue, will give you any additional structural strength. Yes, the foam can fill the joint, which, if it were exposed, might reduce the appearance of a gap -- but the strength of a joint is in the bond between wood fibers. Otherwise, you could just glue end grain to end grain, for example.
If your joint is loose -- and depending on the size of the gap -- you may want to slip a flat handplane shaving or two in the space when doing the glue up. This will increase the long-grain fiber contact and tighten the fit. If the gap is too big, but you still want to use the two pieces, you might consider cutting the tenon off the rail, then cutting a mortise in the end of the rail that is the same size as the mortise in the other part of the chair (the leg, in this case?) and use a correctly sized floating tenon that fits in both mortises.
As far as "best" glue goes, you'll probably get a lot of different ideas, mostly based on personal preference (i.e., what you like to work with), but also based on the anticipated use of the chair. For example, if the chair is going to be used outdoors, you'd want a glue that has water-resistant qualities. In any case, a well-fitting joint is much more important than the type of glue used.
David
"The world that was not made is not won by what is done" -- Mundaka Upanishad
How would an epoxy work in M&T?
Erik, looks like others with more epoxy experience have answered your question for me.
Personally, I have not used epoxy glue specifically for chair joints, although I have used it for other purposes (e.g., when working with an "oily" wood). I think it was Howie who wrote (above) that most glues will weaken over time, and that the failure of a chair joint could be dangerous. I agree in principle, and certainly wouldn't want anyone sitting in one of my chairs to suddenly find themselves sprawled on the floor.
However, I think a "catastrophic" failure of a chair joint (e.g., breakage or fracturing of the wooden parts in the joint) is much more dangerous than, for example, a leg that gets a bit wobbly over time. And to me, a catastophic failure would be the result of a very poorly executed joint or faulty materials, something for which no amount or type of glue could make up, or provide adequate support.
For all of my chairs, and in the chairmaking classes I've taken, hide glue or regular woodworkers' yellow glue have been used (unless I've included a bent lamination, for which I use Unibond 800), the theory being (as I interpret it) that the glue holds the joint together and the joint holds the chair together. For extra security, and if it works with the design, I'll run a dowel or pin through the mortise and tenon joint. Plus, I've always liked the idea that if one of my chairs needs repair later on (generations after I've been buried, I'm sure!), the restorer will be able to take it apart and fix it without having to cut it into pieces.
From what I've seen, a properly designed and constructed chair can stand up to a certain degree of use even before it's glued up... if the joints are well made, I feel quite comfortable dry-fitting the chair and testing it out. The glue helps with all of those odd forces that come from legs being kicked, the chair being dragged on the floor or jumped on, wood swelling and shrinking due to humidity changes, etc.
Anyway, my twenty cents. Others will disagree, I'm sure.
David"The world that was not made is not won by what is done" -- Mundaka Upanishad
All adhesives, except for epoxy, get their strength from close fiber to fiber contact. That's the reason for clamping. The tighter the clamping--within reason--the better the bond.
Poly glues are probably not much stronger than other modern adhesives. While the foam they produce when curing expands to fill gaps, it does not fill the gap with anything that has any strength. Good fitting and tightly clamped joints are required for poly glue and the clamp pressure must be maintained for a number of hours.
Epoxy glue is the exception where the glue itself has strength and adheres strongly to many surfaces. Fill a 1/4" wide gap between two boards with epoxy and it will be as strong as if the two boards were clamped together. In fact, epoxy needs a minimum amount of glueline thickness to develop optimum strength. Clamping too tighly will weaken the joint.
Using epoxy for M&T joints is fine. By their very nature, M&T joints are difficult to clamp and most never apply clamping pressure to the actual faces of the M&T joints. Here the gap filling capability of epoxy will make a stronger joint. For chair making, I only use epoxy as a joint failure can be very dangerous. Most chair joints weaken over time with standard glues but I have never had a failure with epoxy. Like hot hide glue, repair of a failed joint is fairly easy.
Epoxy glues are great. Besides being strong and gap filling, they're easy to color and can be had with a wide range of open times. Probably a lot more advantages too.
But they're not perfect. They're expensive. They're a hassle to mix, and the proportions of resin and catalyst have to be pretty exact. Cleanup is a pain. They're a lot more likely to cause skin reactions than hide glue or white or yellow wood glue.
And they're very permanent. Howie writes, "... repair of a failed joint is fairly easy." I agree, with reservations, but if sound epoxied joints have to be taken apart to fix a piece, that can be difficult to impossible.
Wow. Great info. The joints are snug, but the walls of the mortises are kind of wavy due to my lack of chisel technique, so I know there's not as much surface-to-surface contact as I wanted to see.
So, I'll use epoxy and the minimum clamping necessary to keep the joints attractive. Now, I wonder which epoxies you all like to use. They aren't ALL gap filling are they? And where's your favorite source?
Thanks SO much,
Charlie
Epoxy is great. EXCEPT!!!!!! do not use with red oak. Imagine how you'd feel if your finisher called to tell you while waiting for it's turn for finishing, several joints opened up in that beautiful oak table top you had slaved over. I know. Can you say 'firewood'?
Paul
>>EXCEPT!!!!!! do not use with red oak.
I don't understand. I have eight red oak ladder backed dining room chairs glued with epoxy. They are about 15 years old and no problem. Two are finished with lacquer, the rest with varnish.
I used WEST system epoxy. Even the distributor, Gauguan(sp?) Bros. literature recommends not using WEST system on red oak, which I did not know when I glued up the top. I have been using WEST system for many years & never had a problem in any of my other applications (not red oak). Other epoxies may work OK.
When I got the top home, I placed the top accross the edge of my bench & used hand pressure to split several of the joints apart. Total joint failure with minimal wood transfer.
Paul
Paul, here is note I just recieved from Gougeon.
*******
Oak is a more difficult to bond wood but with proper surface preparation you should have good success. Oak should be sanded with 60 - 80 grit and use only minimul clamp pressure to join. Apply epoxy adhesive to both mating surfaces.
Gougeon Brothers, Inc.
100 Patterson Ave., PO Box 908
Bay City, MI 48707-0908 U.S.A.
*******
Not just oak but any hardwood should be sanded with rough sandpaper and then not over clamped. As I said in my prior responce, epoxy relies on a certain film thickness to properly bond. Overly smooth surfaces and excess clamping will seriously weaken a joint.
Paul,
I read the post below with red oak being referenced on the label. Do you know why not with red oak? Is it the tannin in the wood?
jdg
You want two part, slow set epoxy adhesive. I use mainly ones from marine manufactures but there are others. Some you mix equal parts of the hardener and adhesive, others use unequal proportions. West System makes good products. Just follow the directions carefully.
Make up only what you can use within a short period. While still liquid, you can clean up with acetone but try to minimize squeeze out. You can used acetone to get it off your hands also but it's better to where nitrile gloves.
I'm a West System fan. Jamestown Distributors, on the web and by 800 #, were a pleasure to deal with. They also carry copper nails and roves if you get into riveting.
I used epoxy (and rivets) for the first time to make outdoor benches, which had 44 M&T's in each (total of 5 benches, 200+ M&T's). The things I esp. liked about the West epoxy were: The mix ratio of 5:1 is achieved with one pump stroke of each of the pumps; that there was over 30 min. of open time of the slow set, and the glue lasts for several years, with the pumps in the cans. Just grab and go.
These benches were spanish cedar, which posed no problems at all. Used epoxy also to coat out the bottoms of the 3x3 legs to minimize wicking of water from the ground.
Thanks for the advice; I used a slow set epoxy, and the chair is like a rock. Doesn't budge. Squeezout was minimal. The only caveat was that the parts weren't as true as I'd have liked and more clamping pressure than you recommended was required to square up the chair. I've moved a step forward in my learning pocess, and I'm grateful.
Charlie
Glad it worked Charlie. Now I won't have to stand when I come for dinner.
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