Kia ora, Tatou.
I was idly considering the use of glue whilst watching the excellent series featuring Dan Faia making a chair.
I enjoy making chairs, but have not made many and have of course been inspired as I rather like the Queen Anne style of chair and a few months making a set would be good for me I think.
This led to consideration of whether to use a waterproof adhesive, thinking it would be less likely to fail over time (with no evidence of course to that effect) or a reversible glue, accepting that failure is inevitable, not that unlikely to happen when I am still alive (I’m only 53 so 30-40 years of use for said chairs) and so requiring repair.
Two questions arise, then.
1. Assuming perfect joinery (!) what would be the failure mode of the glue? Does it deteriorate by moisture or oxidation, or simply by mechanical trauma?
2. Is there a longevity advantage of waterproof PVA over say yellow glue or hide glue?
Replies
In a chair, their is a ton of stress. You have very narrow tenons on slim rails, lots of racking and twisting forces I'd think joint failure is bound to happen. When it does, I want hide glue so I can fix it. I've heard conservatory curse a blue streak over repairs made with modern glues.
I dislike waterproof PVAs. When I use yellow glue, I only use Titebond 1. I've never had a failure with it, so I don't feel the need for something "better."
Back in the day, the original Titebond was the only one. Then Titebond 2 came out, and I switched. Must be better, right? When I would inevitably get glue on my hands, I'd wipe it on my shirt. With TB1, it would come right out in the wash. With TB2, it stayed hardened on the shirt. I ruined some clothes using it.
I don't make outdoor furniture, so have no need for waterproof glue. TB1 and liquid hide glue (Old Brown Glue) are pretty much all I need.
I'm not knocking modern glues for the modern items I make because it's really good stuff (like Titebond). But in my years of restoring/repairing very old antique furniture I always try to be respectful of the next guy repairing it a hundred years from now. Hence, on things like that I always use real hide glue. I have repaired stuff that was smeared with modern-day glues and then had to also repair the finish and make new parts in some cases. And hide glue holds incredibly well for it's age.
I have a set of dining chairs that were factory made possibly in the 40s or 50s. My father was gluing them back together in the 60s, using plastic resin glue, and I was again in the 70s using yellow glue. In the early 90s I glued them back together using epoxy, and they have held solid ever since. These were made with dowel joints between the legs and the rails, and for the stretchers. There was an article in FWW years ago on why such dowel joints tend to fail. They have a minimum of side grain in the round holes, and tend to get compressed by seasonal movement beyond the elasticity of the wood fibers, leading to permanent compression.
Epoxy is reversible. I have undone joints using acetone (by recommendation of the epoxy maker's tech guy.) In my case, I drilled a very small hole into the joint, and used a hypodermic needle to inject the acetone for a day or two until the epoxy softened up.
When I make chairs (occasionally), I always use mortise and tenon joints, which have much better strength and durability. If I were concerned with repair reversibility, I would use either Titebond 1 or long set epoxy (which has longer working time, waterproofness, and reversibility.)
This is not to criticize the round-joint hand made chairs made with a combination of green and dry wood that can last for generations.
Wood will expand or contract regardless of which type of glue you use. We will know in a hundred years or so how well epoxy holds up. Expansion will cause compression and hardening the tenon I would think would cause more damage over time. Better to compress the tenon than the mortise when a repair is required I would think. Better to have a glue that is easy to release when you have to take it apart. What we do know is that the pharaohs coffin is still intact....hide glue! Proven product for thousands of years!
I met Steve Smith some years ago at a house party and have had several phone conversations since. He manufactures specialized epoxies and we discussed epoxies for a quite a while. The part that I remember most was the part where he explained, because of the toxic nature of epoxy, " that if you ever develop a reaction to it your done!" This comes from Mr. Epoxy himself! I do use epoxy from time to time but avoid it if I can. I do find it a mess to work with besides. I do alot of bent lamination and because your working fast and handling a lot of material no amount of glove changes prevents you from getting glue everywhere . Epoxy where you dont want it is hard to clean up.
Because of the stress in curved laminations you want a none slip glue. PVA glues tend to slip causing failure. Because of a chairs use or abuse ,chairs can have a hard life ,any type of glue will experience stress and possible failure over time. With that said PVA glues have been used for a long time and do obviously work quite well and I do use it extensively. I'm not knocking it . I think it would be fine for a chair.
Several types of glue tend to not slip and hide glue, particularly hot hide glue, is one of them and is the easiest glue I know of to work with or to clean up. For work that is not intended to spend time outdoors I prefer to use it.
I've been using titebond lll some for outdoor laminations lately because someone says it works, its cheap and available and so far it has worked and I might know for sure in a couple of years.
I've made some very nice and useful pieces of furniture, but no chairs so far. With the pieces I've made, I certainly want my family to have use of them over their lives, but I really haven't looked beyond that. For one thing, popular styles change and tastes change. Since my pieces have solid joints held together with Titebond glues (both waterproof, original, and water resistant extend), I would assume they would hold for at least the length of time my family or I, myself, will use them. There is no reason for them to not last that long unless they are abused (and, if abused, it's likely they would need much more work than just joint repairs). I also think that it's a little bit arrogant and egotistical to believe that my work will be in demand a 100 years in the future. Therefore, I make every effort to make my glue-ups sound and to last for the foreseeable future. I suppose, that runs contrary to the vast majority of woodworkers view of things they make, but I'm making furniture for my family to use and not to see how long it will last.
Your perspective and mine align well. I suspect some bigger pieces will be desired for a while, but as you say, fashions change and I'd hate to think that some poor gggreat grandchild might one day be on Repair Shop or it's then equivalent feeling they have to restore something I made.
For the most part, I use liquid hide glue. There is a long (centuries to millennia) historical track record of how well hide glue holds up and more importantly, how to repair the joint when it becomes loose. I suspect PVA joints can be repaired as well. Just decided to go with what has historically been done and known for a long time.