In 4 decades as a woodworker, I’ve done a good bit of conservation, repair and restoration work, including pieces in a few federal museums both here and overseas. As I pass what I know down to my boys, included will be what I know about glues. I know that some glue types can’t be glued over, often requiring new wood to be let in during repairs, and the joint recut. I discovered that the hard way some decades ago restoring furniture, and simply switched to other glues for all my work. Since then, those glues I rejected may have been reformulated; plus there are a number of new glues worth checking out, so to make sure I’m not providing bad or outdated advice, it’s time to check out the current crop of wood glues for repairability.
I make no pretenses toward science, here…this is all anecdotal based on experience, not chemistry…all I want to show is whether marine epoxy will adhere to the glue lines or residue of the various wood glues during repairs. You can look up strength and other test data in your USDA Wood Handbook; I care about repairability because I’ve never seen any test or even anecdotal data on anything but hide glue in that regard, and it’s important if your work is to survive beyond typical damage and wear and tear over time. I chose epoxy as the regluing agent because it’s the usual choice in professional structural repair work and it adheres to a greater number of diverse substances than any other wood glue I know of. In fact, it usually rebonds a failed but fully cured glue joint much better than the original glue would, and as it also bonds to itself very well, epoxy is a good, repairable choice for many applications.
On identical tiles of freshly planed, vertical grain, second-growth Doug Fir, I saturated the faying surfaces with glue and let them cure to full strength by the manufacturer’s instructions for time and temperature….
…then I keyed each faying surface with 100-grit abrasive paper, reglued them with marine epoxy, and “clamped” the assemblies to the degree favored by epoxy. For glues that left a rough surface like polyurethane, the epoxy was applied twice…an unthickened coat followed by a second coat thickened with West 404 High-Adhesive Thickener, per the manufacturer’s instructions. I let the epoxy cure for 6 days to reach full strength.
I purposely chose small blocks of wood with easily broken short grain because strength here isn’t the issue, adherence is, and I can check adherence using a sharp chisel without trying to break long glue joints in a press. Of greater concern was that the glues to be tested were applied without any clamping pressure, but as it turned out, several glues that require high clamping pressure fared very well, so I believe the results are reasonably valid.
The results offered no surprises.
The epoxy thoroughly adhered to the strongest of the off-the-shelf glues, the 2-part resorcinol, breaking completely at the wood rather than the glue line. Attempts to slip the chisel between the glue lines revealed a thorough and unified bond between all three layers of glue.
Epoxy on epoxy showed similar results……and so did liquid polyurethane (Elmer’s Ultimate)…
…and powdered urea formaldehyde plastic resin glue.
Titebond, a Poly Vinyl Acetate glue, however, broke some wood but failed the chisel test…. the chisel easily separated the two layers of Titebond, indicating poor adherence of the epoxy in between.
Titebond II broke even less wood, with poor adherence…
…and Titebond III, while a much stronger glue, still did not adhere to the epoxy.
The implications of all this can be minor if we are talking about a first-effort coffee table….but they can be serious if we are talking about a strip-planked boat hull made of 1 X 1 strips glued together using an unrepairable glue. Picture the requirement to feather in a large patch to repair hull damage, and you can see that patch will be pinstriped with unsound repair at every glue line, leading to early failure of the repair.
You can draw your own conclusions. Mine are that the work most easily restored is often the work that survives the longest, that you may not care about longevity, but that may break you granddaughter’s heart some day, and I’d check out my glue choices thoroughly before committing them to any 20-hour high-end project, let alone a 700-hour project.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think…that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ –John Ruskin.
Replies
Hi Bob,
Well, that was an interesting exercise! I've heard for years that cured hide glue will stick to new hide glue, but that cured "white" and "yellow" glues won't stick to new applications of same.
Have you any data on cured yellow sticking to fresh yellow, etc?
-Jazzdogg-
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." Bertrand Russell
Nothing I know of in this world adheres to cured Titebond. And I've tried most of them.The usual scenario was a fine, old, round-tenon chair assembled with hide glue. Hide glue is a fully-renewable glue where all you have to do to reglue the joint is soak it in fresh, hot hide glue....30 to 60 minutes to reglue the whole durn chair like new. That's why the builder used a glue that dissolves itself, as the nature of round-tenon joints is that they usually break their glue bonds every 20 years or so from seasonal movement, regardless of what glue was used.But the owner reglued it with whatever PVA glue he had on hand...and that repair lasted a couple weeks. After a few cycles of that, he brings it to me...and it costs him big bucks, because the only way I can repair it is to steam the entire chair apart, then plug and recut the joints he contaminated with PVA.As you can imagine, often the chair became kindling upon receipt of the estimate.<!----><!---->“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Bob,
Thanks for your response: you're preaching to the choir ; - )-Jazzdogg-
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." Bertrand Russell
Bob,
I'm not finding fault with your experiment, but will say that as far as furniture repair goes, I'd be doubtful about the effectiveness of any repair undertaken without cleaning the joint first. (Hide glue regluing a hide glued joint being a possible exception.)
First, many glues are not effective at filling gaps, and this is the cause of failure in many jobs. Addition of more, non-gap-filling glue will not help. An ever-increasingly thick glue line does not allow for proper alignment of a break that was carelessly repaired in the first place.
As you pointed out, compatability between dissimilar glues is also an issue. For example,addition of PVA to hide glue will result in the moisture in the PVA softening the hide glue, allowing them to intermingle to some degree at the interface. PVA/hide glue mixtures have little of the strength of either component, separately.
IMO, the keys to a good repair are:
Good wood to wood fit before applying new glue.
Clean(ed) surfaces to prevent contamination of glue.
Correct amt and direction of clamp pressure.
And in the case of repair to antique furniture, reversibility of the treatment. I try to avoid use of epoxy in furniture repairs solely for this reason.
In your example of the poorly glued chair, my course of treatment involves separation of the loose joints, and cleaning, using appropriate solvents/tools. Care taken to not remove wood from either face of the joint will in many cases, allow for a re-assembly of the joint using appropriate glue, most often, in antiques, hide glue. Plugging and recutting round tenon joints is seldom necessary, unless the hole (usually in the underside of the seat) is really wallowed out. As you stated, many factory made chairs will have their joints loosen, mainly due to their having too-short tenons, and insufficient glue, to begin with. Factory built chairs suffer from starved joints because it takes too long to wipe off squeeze-out. You are so right, that the repair will frequently cost more than the chair is worth.
Use of the techniques you are describing for repair of failed joints in marine applications may very well be good workmanship, and standard practice. It would not be possible or practical to meticulously clean the failed joints on a laminated hull, I'll concede that. Just wouldn't want less experienced folks to extend the same philosophy to putting grandpa's cradle back together.
Regards,
Ray
Thanks for your info, Bob. If I may ask, what's the best way to steam a joint to release the glue?
Wall paper steamer works.
Hide glue is easiest. The "water resistant" glues like resin are difficult. The "waterproof" glues are more difficult but heat will release epoxy and aliphatics.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Edited 6/29/2005 8:51 am ET by Bob Smalser
I was under the impression that vinager fed by a syringe to the Hide Glue joint would make the glue crystalize and the joint 'fall apart'. True?
When you said soak it in hide clue, paint a picture of what you meant by that.
Jerry
Often you don't have to completely disassemble a hide-glued chair....you can warm the joint using a heat gun gently, then work the joint partly apart and wick in fresh, hot hide glue on a brush. And you can go thru and do each joint that way, as in most fine chairs, the stretchers will bend enough to provide the movement required.
But sometimes you do have to completely disassemble the chair if the crystallized glue won't dissolve or the stretchers are too heavy.
No cookie cutters here...this isn't a treatise on regluing a chair....you do what you have to do to get a clean, sound joint.
This is the beginnings of an article for a boatbuilding mag....I left out the 3M 5200, PL Premium and other goos for general consumption, as some of that gunk is still either curing or soaking.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Well, the good news for PL users is that something certainly sticks to PL Premium.
Problem is, I neglected to write down whether it wuz epoxy or more PL and I'll have to run the test again.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Wow! Is that the construction adhesive, or the regular poly glue?"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
PL Premium poly construction adhesive.
Tenacious stuff.“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Bob:Have you ever encountered the Lee Valley "chair doctor" glue? http://www.leevalley.com/wood/page.aspx?c=2&p=30261&cat=1,110
It's apparently thin enough that you can let it seep into a loose joint for repair. Sticking to old glue would be pretty useful there.They suggest unclogging the tip of the glue bottle by soaking in water, so it probably is not of interest to your boatbuilding glue article, but it might allow furniture disassembly. Yes, I could get some and try it myself. I was simply curious to know whether you had done so already.
No, Alan I haven't. I'm building boats now, so chairmaking is largely a past experience.
Resin is more brittle than the others, but not as brittle as hide glue...and will make any interior joint you want to make with it to perfection. Also exterior joints if you keep them painted or varnished - many thousands of varnished, coopered spars have been made with plastic resin since the 1920's with few problems providing the layup was correct and the varnish coat maintained.
Here's the data on resin:
Pot Life - 4-5hrs@70 degrees/2.5-3.5@80/1-2@90.
Open Time - 15min@70 degrees/10@80/5@90.
Closed Time - 25min@70 degrees/15@80/8@90.
Total Time to Assemble - 40min@70 degrees/25@80/13@90.
Clamp Time - 14hrs@70 degrees/8@80/5@90.
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Looks like I got the thick Hotstuff brand cyanoacrylate glue to adhere to the aliphatic Titebonds.
I'll do some more testing with it, but the problem is that cyano is so durn brittle that while it might repair a sliver or a layup, it is totally worthless to repair joints subject to seasonal movement or shock. One bump to that table leg and its reglued mortise and tenon joint will break again.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
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