This series is incredible. Woodworking needs more of this empirical study and analysis to blow away the cobwebs of "common wisdom" that often isn't wise at all.
Dear Patrick, I have now watched all three videos, what can I say but "wow", you have explained so much. Will I watch them again? You bet, there is just so much to take in, Thank you for taking the time and the trouble to produce such finely produced photographs, such clear graphs, and a superb commentary. Regards Chris
You are doing fine work with this series. As someone with science training I appreciate your well thought out approach that makes this work worthy of a paper in a scientific journal. Viewers will now understand PVA glue in ways that will lead to better woodworking. Many thanks.
As a practicing Engineer for 12 years, a University Professor for 25 years, and someone who enjoys woodworking, I appreciate your content. It is science based information about practical applications for the home woodworker, as well as, the more experienced woodworker. Thanks for posting.
Thank you for one of the most educational woodworking videos in existence. You filled in so much of my understanding of gluing and did it in such a concise and clear method. Thank you again.
Excellent demonstration, and comments below. Using shims was an obvious conclusion, but some joint gaps are so narrow that it is hard to find shims that are thin enough, so I am thinking that sprinkling sawdust onto the wet glue before clamping might improve strength.
I'd love to see a test like this using another type of glue, or a single joint tested with various glues. Epoxy, polyurethane, and CA glue are also in my shop. As a mid-level hobby woodworker, I can get many simple joints to well within 0.5mm, but I do think of 10 thousandths of an since, 0.25mm as the practical limit for simple joints. Some joints have inherent strength that does not depend on the glue, so I don't worry too much about the glue in a dovetail or a through mortise. They have enough mechanical strength. Is it possible that epoxy is best for mortise and tenon and CA glue is ideal for dovetails? Interesting to think about; no shortage of stuff to learn. Thanks for contributing to woodworking.
Please don’t forget aliphatic resin (yellow glue). Edit: it would make sense to me if all glues that cure via evaporating solvents were similarly non-gap filling. Please test that too. This is gold!
Fine Woodworking magazine published a rigorous test in August 2007 comparing different glues. Basic take-aways - PVA and epoxy are the strongest, hide glue (either kind) is somewhat less strong - but still very good, and polyurethane is weaker still and especially terrible on loose joints. Epoxy is the only adhesive with any significant gap-filling capability. The wood affects things too, different glues performed a little better on different woods - maple vs oak vs ipe. Also - fitting your joints well is important. Their definitions - tight = 0.0mm clearance, snug = 0.1mm (0.004"), loose = 0.2mm (0.008"). Any larger gaps need fixing - a 0.5mm gap is not a joint, that's a chasm that needs filling.
@@Jeffsd17 Good info, thanks. The test results seem to varie quite alot between different test setups. There are many variables involved. The conclusions that I have made is that I use PVAc for indoor- and epoxy for outdoor applications, no further thinking needed for me.
Really impressed with your scientific approach, depth of thought, and data on this subject. You are improving the woodworking community with high quality information here. Thank you.
Brilliant as always Patrick, thank you. Yeah, I ran into this with a big wardrobe I'm making...some of the dovetails had 1/32" gaps. I made shims and glued them in. No one will see these joints. Good stuff, keep making more amazing, intelligent videos.
I love the work you are doing Patrick! As others have suggested, I would love to see a measurement of joint strength for other glues which are touted as "gap filling" such as epoxies and urea-formaldehyde (UF) glues. My favorite UF glue is Unibond 800, which is touted as having better gap filling abilities because it does not use water as a solvent, but instead uses furfuryl alcohol as a solvent, which does not evaporate, but instead incorporates into the ultimate glue bond, and therefore does not shrink like PVA glues. Keep up the great work!
Just to point out to anyone using UF glues the safety issues should you ever cut it or in any way huff the stuff. If you sell your products there are also restrictions in many countries with controls and required warnings about the formaldehyde content. And it does evaporate- slowly over many years. isn't usually an issue unless you have a lot of it around. IIRC it gases off most when near some heat source. Something to look into. Obviously you can't use it in food products, children's toys, anything really that is likely to be near a mouth intended or not. Just a heads up to use that kind of stuff responsibly.
Most plywoods are made using UF glues, so it is certainly OK to cut it. UF glues were reformulated in the last couple of decades to greatly reduce off-gassing of formaldehyde, which was the greatest concern, but is no longer an issue. While using the glue, while the glue is still wet, it is a good idea to wear a respirator and have good ventilation, but once dry there is no concern. So yes, use of UF glue takes more precaution than typical yellow glue, but once dry, no concern. Same is true of epoxy really
Patrick, Great confirmation about the inherent strength characteristics of PVA glue; gaps are weak. I have played with drying strips of glues on old Teflon lined pans, including PVA and epoxy’s with, and without micro fillers. The PVA breaks easily just like when we break a dried run on the side of our glue bottle. The epoxy, depending upon the type selected, has much more inherent strength. I would love to have quantitative information about the strength characteristics of Epoxy and polyurethane adhesives like the West Systems products commonly used in marine boat building. I guess adhesives are a lot more complicated than one would think. You analysis of PVA commonly used by woodworkers is terrific and should give all cause to learn more about our options and how to select the best product for a particular application. Many thanks for all the time and effort you are putting into this series. Cheers, Will
Excellent and very informative! I came away with a few more thoughts: 1) in type 2 joints where the strength is critical, use a curing adhesive with minimal shrinkage, like epoxy. 2) based on your other video about grain direction, end grain shims might perform better. As I write this, it occurs to me that if shims work by filling the gap with wood, then perhaps a thick paste of sawdust and PVA might work as well or better, provided you apply a thin coat of glue the joint surfaces to ensure they are wet. 3) There is enough strength after about an hour that, at least for small items that don’t weigh much, they can be handled and worked on 4) Unclear to me what clamping contributes to joint strength after the first few minutes post assembly. The pressure does ensure that the joint will be assembled with as thin a film as possible, but It seems that unless the joint is constrained under tension, the glue’s shrinkage will draw the joint together anyway. These tests only addressed the effect of fit, but there is also the effect of moisture. My guess is that it will take longer to cure and will never achieve the full strength of dry. I’m also curious about the effect of the joint being disturbed during its cure. My guess is that that once a decent tack is present, moving the joint can’t be helpful, but I’m prepared to be surprised by another of your excellent studies. Maybe you should get a sponsorship from Instron!
Thank you Mr. Sullivan. This is probably why many woodworkers don’t respect glue strength. Glue is not as effective unless you start with very precise surfaces. Your videos are a gift to the hobby.
True, glue is the best if you know what you're doing. They glue planes together, but it has to perfect! Clean and no gaps. So for most normal people a nail or screw is better.
Thanks for doing and sharing. Remember….The only difference between having fun by screwing around and having fun doing science is writing stuff down. I am glad you are having fun with science.
I viewed this video on my Saturday lunch break and after lunch I was going out to begin a laminated glue-up of my Moravian workbench top. Before this upcoming operation I used polyurethane construction adhesive to laminate boards for the legs. I recently purchased a pint of Titebond III and intended to use it for the benchtop glue-up. After watch this video I’m going to stay with polyurethane construction adhesive. Thanks for doing the in-depth analysis on this series Patrick. Very helpful and insightful. Your results seem to refute the old saying about “starving the glue joint”!
@@fiver-hoo absolutely learned from John. I’ve been using it frequently since he first mentioned it quite a while back. Great product, so much better than Liquid Nails.
Someone once said that if you cannot express your ideas or knowledge in numbers then you really don't know what you are talking about. Clearly, you know what you are talking about. Thanks
Geat work Patrick, I admire your dedication! One thing come to my mind while watching this. Actually two: - does glue pre-soaking of moisture hungry parts like endgrain on softwoord help to strenghten the joint? - does fine sanding of the butt joint affect glue strength? Thanks for your research! Z
very interesting, thank you for doing these videos. A potential suggestion, how about a filler in PVA, like wood dust, how does that effect gappy joint strength and is there a optimum ratio of dust to pva, how about particle size? I expect you'll have endless questions, thanks for doing the research.
I am so impressed with your exploration. It's fascinating. This one is a bit scary for me - a newbie woodworker. I'm trying my best to be as precise as I can when I cut pieces, and this underscores the need to re-double that effort. There are so many factors in play - sequence of cut (for consistent cut settings), feed rate, quality of feed, and I'm sure other factors. It's a beautiful challenge, and I love it! Also, your video quality is exemplary. Thanks very much Patrick.
Patrick, Your experiments are exciting to an old woodworker. I’m learning tons. Thank you for all the effort put into these videos. Like some of the other commentators I’m interested in how epoxy glue, with and without, the micro filler additive compares. Cheers, Will
I'm late to the party, but would love to see more! I appreciate your thoughtful and scientific approach to woodworking. I would like to make a suggestion for a video- would you please consider one to help with common tasks, demonstrating the usual mistakes, precautions to avoid them, and suggesting fixes if (when) they still end up with problems? Thank you so much for your wisdom and sharing your experience- and experiments!
Another excellent video. Thank you, Patrick! One thought/reaction as someone interested in the history of furniture (1600 - today): I wonder how a 'reputedly inferior but (slightly) gap-filling' glue such as hide glue works vs. PVA.
I've seen it recommended to mix sawdust with glue to fill gaps. I imagine that's mostly for the visual but I wonder if it would also help significantly with the strength too
I do use it aswell. Sawdust will press nicely and it helps to fill larger voids. And as this video shows: less glue = more strength. I doubt it will be by much thought and I would love to see some test :)
Okay great video and I love that you didn't shy away from showing the data. Another thing to test I've often seen people add sawdust to pva glue to make their own wood filler and I wonder if that could add back in some strength to the glue joint.
I did a similar experiment at work over a decade ago gluing Baltic birch plywood together with tongue and groove joints, tested for ultimate tensile strength with the joint in tension. For PVA glue a 5 to 10 thou (0.13 to 0.25 mm) gap in clearance of total width between the tongue and groove produced the strongest joints. Samples were clamped for 2 hours, clamps then removed and samples cured in an environmental chamber at 30% RH / 22 deg C for 96 hours.
Another great video!! This might be my favorite so far. I’ll be directing many people to this video over the coming years, when I want to explain/warn of filling gaps with PVA.
When choosing adhesives (typically epoxies) in the lab, I always read the manufacturer's data sheets. They always say to use as thin a bond line as possible - ie, smallest possible gap. This was typically for non-absorbent surfaces. For gluing wooden joints with excessively thick gaps, wouldn't it make sense to add fine sawdust to the glue? I'd love to see some measurements on bond strength vs sawdust fraction for a standard wide gap.
That's a good thought, and I would go one further and say that almost any kind of filler would work, or at least help. A mineral filler like very fine sand or clay or talc would probably do the job. Anything that reduces the volume of the glue will reduce the shrinkage. The down side is that it also reduces the workability of the glue -- makes it stiffer and less flowing. That might be a plus in some situations, not in others. Interesting.
So Paul, what kind of lab do you work in? I work in a state DOT lab testing Portland cement and mineral additives that also go into concrete. Our adjacent concrete lab tests Portland cement concrete, but also does quite a bit of work with polyester concretes.
@@MrBebopChamploo I was thinking the same thing when he showed the joints with the cup and the "foreign object". I have tried the salt trick once...and that was enough for me. Not a fan, and this video reinforces my decision.
I wouldn't think to use use glue+sawdust on joints, but I often use it as a filler! So I think that's a much better contender for a gap-filling wood adhesive than wood glue on its own; I'd be really interested to see that tested.
Wow this is very very interesting 🤔 At school for cabinet making , i’ve lerned that we needed to scuff a smooth surfice (only on the end grain) with our chisel . That way the glue would have more strength , like the peace of pine and maple you’ve showed . It would be nice to have a test on that . The teachers they were saying , the more glue surfice you have the better 😏 Now i know why i’m always going for perfection 🤷🏻♂️😉😜🇨🇦❤️
If I correctly understand your evidence then the old admonition I would get as an apprentice and which I practice to this day is, wet end grain joints with a thin first coating then let them dry to tackiness (which under some circumstances is minutes or even seconds) and then apply another coat before clamp up. Giving your findings on water content and shrinkage the procedure seems to be best practice. Thanks Patrick
Super informative video and well made! this has always been a sort of point of debate in the shop as even though common knowledge is to wait an hour, i have gotten away with 30 minute or even 20 minute clamp times, and this video helped me to understand more of the details behind why and how, so thank you.
This is great data! I’m an amateur luthier and so many acoustic guitar joints are based on various arcs. Achieving tight joints can be very challenging, especially when operations are not performed by CAD/CAM. Still, I prefer one-off by-hand operations. So satisfying when the instrument stays in one piece as string force is applied! And if it also looks sounds and looks good…nothing compares in my woodworking experience!
Great stuff again! I would expect that end-grain joints, although you've shown them to be stronger when glued perfectly, suffer more than side-grain joints when a gap is present, due to more of the PVA solids being absorbed into the wide capillaries. It would be an interesting next step to test this.
👏👏👏 This video is amazing, it helped so much. It solved all my dilemma about PVA glue... I was adding more glue to untight areas in the joint, but at the same time notice the gaps after the glue dries, especially in the side to side glue ups. Now I know what to do, if the joint became a bit loose in some areas, just add more thin piece of wood... Actually there were times that I did that, and was surprised with the strength, but it was confusing me as I thought, adding more glue should hold better! ... Thank you👍
Wow. Just WOW.... This is an astonishing revelation. I have always strived for tight joints, but to realize that 0.5mm is enough to weaken a joint by around half is mind blowing!
Beautifully made points. These points go hand in hand with your previous videos. It absolutely proves that one needs to pay as much attention as possible to the surfaces to be joined, where glue will be applied. It leads me even further into believing that loose tenon joinery (if done properly) could be at least as strong, if not stronger, when compared to a regular tenon. I really will have to test it once the warm weather hits! I'm curious to know how long PVA glue survives... I'm guessing the Egyptian chair was made with a form of hide glue? I wonder how long PVA glue will last in modern projects. I wonder if it would last 3500 years. I can't imagine why not.
Wonderful series of videos. Who knew glue could be so interesting, especially given a topic that is basically about "let's watch glue dry". I'd really like to see some real data on how important (or not) it is to put glue on both surfaces. Also as an extension to the current video, how does adding salt (to reduce slippage) impact the strength of the glue joint.
As a beginner fumbling my way through a first project I have to first thank you for this series. This information is invaluable! I also have a question. Have you ever tested some other ways of filling the gaps? For example, creating a poor man's composite material out of pva glue + cotton, or sawdust? From your test it looks as though the glue's surface tension is trying to create a minimum surface as water is lost, and by adding some fibrous, space-filling material, the shrinkage should be more even and result in a more regularly spaced (and hopefully stronger) lattice. Once again thanks for the content!
Thanks for the facts. I hope you stick to what You want to test and not get distracted by what others want you to do, which is what they themselves should do.
Really solid research, I tend to use PU glue when I can't properly control for gaps (for example hidden dowels), but how is it for strength compared to PVA?
Your methods are superb and thus provide useful insights, so thank you for taking the trouble to both think through the issues and design appropriate tests. I wonder if adding saw dust to the glue to varying concentrations impact the joint strength?
@@MiniLuv-1984 Yea, if the apparent cause of weakness in a joint is water evaporation, well try to reduce the amount of glue in the joint. You can do that with perfectly mated surfaces, or you could use a matrix. And no one says it has to be specifically sawdust. I note from wiki wood has 10% or more water absorption, while FRC is 0.3% and below. While nicely mated surfaces is doable once you have some skill, until you reach that point, here's another option that might actually be stronger and more forgiving.
I really enjoy your investigations. If pushing the limits (model airplanes, speed boats, portable cases, etc.) this is incredibly important. But, for most woodworking projects you aren't trying to minimize weight or size - often a design is "beefy" or "chunky" on purpose, and in these situations sloppy joints are still strong enough for any forces the joint will experience in normal use. If a gap is glue's Achilles heel, suface area is glue's secret weapon. If your joints are sloppy keep going!
This was a really good video and it was devastating to see the difference in 0,5mm gaps. I would also like to see what could be done with different kinds of glues, even if they ”should” not be used in woodworking.
Excellent content and presentation, as always. I wonder what improvement could be made on one of the test joints if the glue was bulked up with sawdust, for those occasions when the joint is a real disaster, and you need to rescue it fast? That might be a useful follow up to this experiment.
I have another tip for you- cocktail sticks. You can drill out the right size hole and glue them in like miniature dowels. It's another way to fix something that is breaking over time without breaking it apart. You'd think they wouldn't be that strong, but with pva glue and due to the forces being over a small part of the cocktail sticks and the grain being the right way, they are pretty strong. It obviously has certain best use cases - tension forces, where a tac or nail won't help. A joint that comes loose can be held tight again - its a repair tip really. however it is also very discrete and professional looking. You can also experiment with paper/card just as well as sawdust if it more suits the application, as you can pressure paper in to a crevice which you cannot do with sawdust pva mix. I'm not sure if that is actually stronger at all, and you have to chose between sawdust, paper and a wedge of wood or popsicle stick depending on the size of the gap. Alas, that is what Mr Sullivan is here for.
Firstly, I've read many of the comments below and I'm impressed by how constructive and inquisitive they are! These are questions that we have all pondered in one way or another, but never really answered. Brilliant information, thank you so much, you have convinced me to use screws in future, LOL only joking.
Very useful and appreciated. Perhaps dowels and/or pocket screws would provide a joint of preferable strength so long as they were usable on a given project. My limited experience suggests that properly installed dowels should have very small gaps between the dowel and the board in which it is installed providing optimal glue surfaces.
Pretty interesting results indeed, Patrick! Thanks a lot! 😃 What about the salt trick? I wonder if it affects the glue up. Anyway, stay safe there with your family! 🖖😊
@@MCsCreations I agree it would be an interesting test. It's just fun to think about it. The alternative would that the salt could act like debris in the joint.
Thank you for the insightful video as always. Dr. Sullivan, would you be able to comment about the safety of the PVA glues as an internal medicine practitioner? I know titebond II and III are FDA approved for indirect food contact. However, I would like to know the science behind that more in detail.
Thanks. I've always wondered if glue needs to be applied to both sides of a joint and if lightly dampening the wood before applying the glue would increase joint strength?
Your excellent work seems to indicate that clamping really is key. It makes me think that joints should be clamped as tight as possible and left in place until the glue has fully cured. Maybe clamp-time vs joint-strength is worth testing.
Another GREAT video!! Two questions: Your initial chart, based on something that has 100% strength, does not indicate when it reaches 100%??? And, your summary discussion of filling the joint gap with a shim begs the question: What if you added sawdust to the glue, to create a sponge-like area for the glue to bind to?
Hi Patrick. This is another great video. I understand that this is not part of the "glue science" so it isn't necessarily applicable here. I'd like to see a strength comparison between a gap filled with wood vs one filled with a gap-filling epoxy.
There is a trick to recovering a loose joint. Dry fit, and mark the gaps. If it's a mortise and tenon, and you've over planed the cheeks of the tenon, check to see where the lost thickness is. If it is symmetric, all to the good. If not, things get fussier. Spread PVA on the cheek of concern, and then press paper on to it. Regular white bond is fine. You don't need or want a polished finish. Cover that with either a piece parchment paper or some other material that the glue won't adhere to. You can think of this as paper shimming, with the paper as bulk that excludes excess glue. Let it dry thoroughly - at least 24 hours, 48 or more is better. Check the fit, correct as needed (it won't be as easy as cleaning up clean wood), and glue up the joint. I started thinking about this while dissecting a Victorian mortise and tenon joint that had paper glued in with hide glue. I have also seen this on shoulder correction.
I am quite sure that adding a shim of veneer works to boost the joint strength of a loosely fitted joint. The question of what other materials also work remains open in my mind. Many people use sawdust, and claim it works. This is harder for me to test in a rigorous way. However, your concept that paper will also do the job is intriguing. I have not tested this, but my hunch is that filling the loose space with paper is probably much better than trying to fill the space with glue. Thanks for the tip.
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This series is incredible. Woodworking needs more of this empirical study and analysis to blow away the cobwebs of "common wisdom" that often isn't wise at all.
Dear Patrick, I have now watched all three videos, what can I say but "wow", you have explained so much. Will I watch them again? You bet, there is just so much to take in,
Thank you for taking the time and the trouble to produce such finely produced photographs, such clear graphs, and a superb commentary.
Regards
Chris
You are doing fine work with this series. As someone with science training I appreciate your well thought out approach that makes this work worthy of a paper in a scientific journal. Viewers will now understand PVA glue in ways that will lead to better woodworking. Many thanks.
As a practicing Engineer for 12 years, a University Professor for 25 years, and someone who enjoys woodworking, I appreciate your content. It is science based information about practical applications for the home woodworker, as well as, the more experienced woodworker. Thanks for posting.
IMO the glue companies should hire you as a consultant! Brilliant work. And each our your findings open up even more questions!
I appreciate the quality of the information and presentation in all of Mr. Sullivans videos.
Thank you for one of the most educational woodworking videos in existence. You filled in so much of my understanding of gluing and did it in such a concise and clear method. Thank you again.
Excellent demonstration, and comments below. Using shims was an obvious conclusion, but some joint gaps are so narrow that it is hard to find shims that are thin enough, so I am thinking that sprinkling sawdust onto the wet glue before clamping might improve strength.
Interesting hypothesis. I'd like to see Patrick test it. The purpose of the shim is to use the lignin, the sawdust might fill enough of the gaps.
I had the same thought. This really needs to be tested! Maybe a bit more than a "sprinkle" of sawdust though!
I'd love to see a test like this using another type of glue, or a single joint tested with various glues. Epoxy, polyurethane, and CA glue are also in my shop. As a mid-level hobby woodworker, I can get many simple joints to well within 0.5mm, but I do think of 10 thousandths of an since, 0.25mm as the practical limit for simple joints. Some joints have inherent strength that does not depend on the glue, so I don't worry too much about the glue in a dovetail or a through mortise. They have enough mechanical strength. Is it possible that epoxy is best for mortise and tenon and CA glue is ideal for dovetails? Interesting to think about; no shortage of stuff to learn. Thanks for contributing to woodworking.
And the average plastic glue gun :)
Search YT for "wood by wright glue test".
Please don’t forget aliphatic resin (yellow glue).
Edit: it would make sense to me if all glues that cure via evaporating solvents were similarly non-gap filling. Please test that too. This is gold!
Fine Woodworking magazine published a rigorous test in August 2007 comparing different glues. Basic take-aways - PVA and epoxy are the strongest, hide glue (either kind) is somewhat less strong - but still very good, and polyurethane is weaker still and especially terrible on loose joints. Epoxy is the only adhesive with any significant gap-filling capability. The wood affects things too, different glues performed a little better on different woods - maple vs oak vs ipe. Also - fitting your joints well is important. Their definitions - tight = 0.0mm clearance, snug = 0.1mm (0.004"), loose = 0.2mm (0.008"). Any larger gaps need fixing - a 0.5mm gap is not a joint, that's a chasm that needs filling.
@@Jeffsd17 Good info, thanks. The test results seem to varie quite alot between different test setups. There are many variables involved.
The conclusions that I have made is that I use PVAc for indoor- and epoxy for outdoor applications, no further thinking needed for me.
Really impressed with your scientific approach, depth of thought, and data on this subject. You are improving the woodworking community with high quality information here. Thank you.
Great video! I have so often wondered why my clamps were loose after a few hours of curing. Thanks for the answer!
Amazing and very useful! Thank you, Patrick! It is for thousands of woodworkers for now and in the future👍
Brilliant as always Patrick, thank you. Yeah, I ran into this with a big wardrobe I'm making...some of the dovetails had 1/32" gaps. I made shims and glued them in. No one will see these joints. Good stuff, keep making more amazing, intelligent videos.
I love the work you are doing Patrick! As others have suggested, I would love to see a measurement of joint strength for other glues which are touted as "gap filling" such as epoxies and urea-formaldehyde (UF) glues. My favorite UF glue is Unibond 800, which is touted as having better gap filling abilities because it does not use water as a solvent, but instead uses furfuryl alcohol as a solvent, which does not evaporate, but instead incorporates into the ultimate glue bond, and therefore does not shrink like PVA glues. Keep up the great work!
Just to point out to anyone using UF glues the safety issues should you ever cut it or in any way huff the stuff. If you sell your products there are also restrictions in many countries with controls and required warnings about the formaldehyde content. And it does evaporate- slowly over many years. isn't usually an issue unless you have a lot of it around. IIRC it gases off most when near some heat source. Something to look into. Obviously you can't use it in food products, children's toys, anything really that is likely to be near a mouth intended or not.
Just a heads up to use that kind of stuff responsibly.
Most plywoods are made using UF glues, so it is certainly OK to cut it. UF glues were reformulated in the last couple of decades to greatly reduce off-gassing of formaldehyde, which was the greatest concern, but is no longer an issue. While using the glue, while the glue is still wet, it is a good idea to wear a respirator and have good ventilation, but once dry there is no concern. So yes, use of UF glue takes more precaution than typical yellow glue, but once dry, no concern. Same is true of epoxy really
Patrick, I absolutely love the scientific approach you've taken with this series. Absolutely fantastic.
Patrick, Great confirmation about the inherent strength characteristics of PVA glue; gaps are weak. I have played with drying strips of glues on old Teflon lined pans, including PVA and epoxy’s with, and without micro fillers. The PVA breaks easily just like when we break a dried run on the side of our glue bottle. The epoxy, depending upon the type selected, has much more inherent strength. I would love to have quantitative information about the strength characteristics of Epoxy and polyurethane adhesives like the West Systems products commonly used in marine boat building. I guess adhesives are a lot more complicated than one would think. You analysis of PVA commonly used by woodworkers is terrific and should give all cause to learn more about our options and how to select the best product for a particular application. Many thanks for all the time and effort you are putting into this series. Cheers, Will
Excellent and very informative!
I came away with a few more thoughts:
1) in type 2 joints where the strength is critical, use a curing adhesive with minimal shrinkage, like epoxy.
2) based on your other video about grain direction, end grain shims might perform better. As I write this, it occurs to me that if shims work by filling the gap with wood, then perhaps a thick paste of sawdust and PVA might work as well or better, provided you apply a thin coat of glue the joint surfaces to ensure they are wet.
3) There is enough strength after about an hour that, at least for small items that don’t weigh much, they can be handled and worked on
4) Unclear to me what clamping contributes to joint strength after the first few minutes post assembly. The pressure does ensure that the joint will be assembled with as thin a film as possible, but It seems that unless the joint is constrained under tension, the glue’s shrinkage will draw the joint together anyway.
These tests only addressed the effect of fit, but there is also the effect of moisture. My guess is that it will take longer to cure and will never achieve the full strength of dry.
I’m also curious about the effect of the joint being disturbed during its cure. My guess is that that once a decent tack is present, moving the joint can’t be helpful, but I’m prepared to be surprised by another of your excellent studies. Maybe you should get a sponsorship from Instron!
Thank you Mr. Sullivan. This is probably why many woodworkers don’t respect glue strength. Glue is not as effective unless you start with very precise surfaces. Your videos are a gift to the hobby.
True, glue is the best if you know what you're doing. They glue planes together, but it has to perfect! Clean and no gaps. So for most normal people a nail or screw is better.
Thanks for doing and sharing. Remember….The only difference between having fun by screwing around and having fun doing science is writing stuff down. I am glad you are having fun with science.
Patrick, THANK YOU very much for this series!! Your videos are very enlightening.
I viewed this video on my Saturday lunch break and after lunch I was going out to begin a laminated glue-up of my Moravian workbench top. Before this upcoming operation I used polyurethane construction adhesive to laminate boards for the legs. I recently purchased a pint of Titebond III and intended to use it for the benchtop glue-up. After watch this video I’m going to stay with polyurethane construction adhesive.
Thanks for doing the in-depth analysis on this series Patrick. Very helpful and insightful. Your results seem to refute the old saying about “starving the glue joint”!
John Heisz stamp of approval
@@fiver-hoo absolutely learned from John. I’ve been using it frequently since he first mentioned it quite a while back. Great product, so much better than Liquid Nails.
Your videos are so enlightening. Thank you so much for the hard work you have put into these experiments.
Your videos been eye popping. I really really really appreciate for putting soooo much efforts in these and sharing them with us.
Someone once said that if you cannot express your ideas or knowledge in numbers then you really don't know what you are talking about. Clearly, you know what you are talking about. Thanks
Geat work Patrick, I admire your dedication! One thing come to my mind while watching this. Actually two:
- does glue pre-soaking of moisture hungry parts like endgrain on softwoord help to strenghten the joint?
- does fine sanding of the butt joint affect glue strength?
Thanks for your research!
Z
very interesting, thank you for doing these videos. A potential suggestion, how about a filler in PVA, like wood dust, how does that effect gappy joint strength and is there a optimum ratio of dust to pva, how about particle size? I expect you'll have endless questions, thanks for doing the research.
One vote for the filler strength test
Another vote here
This series of videos has been fascinating. Many thanks for contributing to our collective woodworking knowledge. Keep up the good work.
I am so impressed with your exploration. It's fascinating. This one is a bit scary for me - a newbie woodworker. I'm trying my best to be as precise as I can when I cut pieces, and this underscores the need to re-double that effort. There are so many factors in play - sequence of cut (for consistent cut settings), feed rate, quality of feed, and I'm sure other factors. It's a beautiful challenge, and I love it! Also, your video quality is exemplary. Thanks very much Patrick.
Once again, thank you for your research. It's some of the best woodworking info on TH-cam.
Once again, great data. Thanks for going the extra mile examining imperfect joints.
Patrick, Your experiments are exciting to an old woodworker. I’m learning tons. Thank you for all the effort put into these videos. Like some of the other commentators I’m interested in how epoxy glue, with and without, the micro filler additive compares. Cheers, Will
I'm late to the party, but would love to see more! I appreciate your thoughtful and scientific approach to woodworking. I would like to make a suggestion for a video- would you please consider one to help with common tasks, demonstrating the usual mistakes, precautions to avoid them, and suggesting fixes if (when) they still end up with problems? Thank you so much for your wisdom and sharing your experience- and experiments!
fantastic progression of glue science! Please keep these coming!
Such a helpful series. Thanks a lot! I really appreciate your precision and attention to detail.
Excellent analysis, method and presentation! And thankyou for sharing! Great work!
Another excellent video. Thank you, Patrick!
One thought/reaction as someone interested in the history of furniture (1600 - today): I wonder how a 'reputedly inferior but (slightly) gap-filling' glue such as hide glue works vs. PVA.
I've seen it recommended to mix sawdust with glue to fill gaps. I imagine that's mostly for the visual but I wonder if it would also help significantly with the strength too
I do use it aswell. Sawdust will press nicely and it helps to fill larger voids. And as this video shows: less glue = more strength. I doubt it will be by much thought and I would love to see some test :)
Thank you for taking the time and effort to do these experiments
This is very helpful information Patrick. I cannot thank you enough
Your very thorough research and well thought out tests resulted in some very interesting & useful information. Thanks Patrick!
Okay great video and I love that you didn't shy away from showing the data.
Another thing to test I've often seen people add sawdust to pva glue to make their own wood filler and I wonder if that could add back in some strength to the glue joint.
🤔 thinking the same!
Epoxy and wood flour or microfibers???
I'm pretty sure this is weaker than thick glue by itself.
Extremely interesting and practical especially as an professional furniture maker
I did a similar experiment at work over a decade ago gluing Baltic birch plywood together with tongue and groove joints, tested for ultimate tensile strength with the joint in tension. For PVA glue a 5 to 10 thou (0.13 to 0.25 mm) gap in clearance of total width between the tongue and groove produced the strongest joints. Samples were clamped for 2 hours, clamps then removed and samples cured in an environmental chamber at 30% RH / 22 deg C for 96 hours.
Another great video!! This might be my favorite so far. I’ll be directing many people to this video over the coming years, when I want to explain/warn of filling gaps with PVA.
When choosing adhesives (typically epoxies) in the lab, I always read the manufacturer's data sheets. They always say to use as thin a bond line as possible - ie, smallest possible gap. This was typically for non-absorbent surfaces.
For gluing wooden joints with excessively thick gaps, wouldn't it make sense to add fine sawdust to the glue? I'd love to see some measurements on bond strength vs sawdust fraction for a standard wide gap.
That's a good thought, and I would go one further and say that almost any kind of filler would work, or at least help. A mineral filler like very fine sand or clay or talc would probably do the job. Anything that reduces the volume of the glue will reduce the shrinkage. The down side is that it also reduces the workability of the glue -- makes it stiffer and less flowing. That might be a plus in some situations, not in others. Interesting.
So Paul, what kind of lab do you work in? I work in a state DOT lab testing Portland cement and mineral additives that also go into concrete. Our adjacent concrete lab tests Portland cement concrete, but also does quite a bit of work with polyester concretes.
@@BLenz-114 this makes me wonder about the impact of table salt, which I’ve used in some glue ups to keep things from sliding around.
@@MrBebopChamploo I was thinking the same thing when he showed the joints with the cup and the "foreign object".
I have tried the salt trick once...and that was enough for me. Not a fan, and this video reinforces my decision.
I wouldn't think to use use glue+sawdust on joints, but I often use it as a filler! So I think that's a much better contender for a gap-filling wood adhesive than wood glue on its own; I'd be really interested to see that tested.
Wow this is very very interesting 🤔 At school for cabinet making , i’ve lerned that we needed to scuff a smooth surfice (only on the end grain) with our chisel . That way the glue would have more strength , like the peace of pine and maple you’ve showed . It would be nice to have a test on that . The teachers they were saying , the more glue surfice you have the better 😏
Now i know why i’m always going for perfection 🤷🏻♂️😉😜🇨🇦❤️
If I correctly understand your evidence then the old admonition I would get as an apprentice and which I practice to this day is, wet end grain joints with a thin first coating then let them dry to tackiness (which under some circumstances is minutes or even seconds) and then apply another coat before clamp up. Giving your findings on water content and shrinkage the procedure seems to be best practice. Thanks Patrick
This is tremendously valuable information and a wonderful alternative to blind faith in strongly held beliefs based on nothing whatsoever.
Mr. *Sullivan's* scientific approach is almost unrivaled. In this regard, only Matthias Wandel can hold him a candle.
Super informative video and well made! this has always been a sort of point of debate in the shop as even though common knowledge is to wait an hour, i have gotten away with 30 minute or even 20 minute clamp times, and this video helped me to understand more of the details behind why and how, so thank you.
Just wow. Fantastic analysis.
This is great data! I’m an amateur luthier and so many acoustic guitar joints are based on various arcs. Achieving tight joints can be very challenging, especially when operations are not performed by CAD/CAM. Still, I prefer one-off by-hand operations. So satisfying when the instrument stays in one piece as string force is applied! And if it also looks sounds and looks good…nothing compares in my woodworking experience!
Great stuff again! I would expect that end-grain joints, although you've shown them to be stronger when glued perfectly, suffer more than side-grain joints when a gap is present, due to more of the PVA solids being absorbed into the wide capillaries. It would be an interesting next step to test this.
👍yes, that would be a great video
Can't wait for the Fifth in this series. Take care Patrick. -Mike
👏👏👏 This video is amazing, it helped so much. It solved all my dilemma about PVA glue... I was adding more glue to untight areas in the joint, but at the same time notice the gaps after the glue dries, especially in the side to side glue ups. Now I know what to do, if the joint became a bit loose in some areas, just add more thin piece of wood... Actually there were times that I did that, and was surprised with the strength, but it was confusing me as I thought, adding more glue should hold better! ... Thank you👍
This is fantastic information. Thank-you for arming me with this knowledge!
Wow. Just WOW.... This is an astonishing revelation. I have always strived for tight joints, but to realize that 0.5mm is enough to weaken a joint by around half is mind blowing!
YES! I have noticed reduced pressure when removing panels from the clamps. Now I know why! Thanks!
What an eye opener! Great food for more thought.
Excellent information! I wonder if sawdust mixed with glue would be as effective at a wooden shim? I really enjoy these videos
Was thinking the same thing - like aggregate in concrete.
If the mixture is 50% PVA and 50% sawdust by volume, then there will still be about 25% water in the mixture that will evaporate.
This video should be promoted as "must see" for every woodworker that uses glue in his/hers joinery :)
Wow great info and video as usual. You are really changing the way current and future generations think about these concepts! Thanks!!
An old Cornish boy needs help. It’s a very genuine enquiry. When gluing up a series of long mitres 3 inches, making a frame.
Thank you for this methodical analysis! I am learning a lot.
Just fantastic. Thank you for this video!
Beautifully made points. These points go hand in hand with your previous videos. It absolutely proves that one needs to pay as much attention as possible to the surfaces to be joined, where glue will be applied. It leads me even further into believing that loose tenon joinery (if done properly) could be at least as strong, if not stronger, when compared to a regular tenon. I really will have to test it once the warm weather hits! I'm curious to know how long PVA glue survives... I'm guessing the Egyptian chair was made with a form of hide glue? I wonder how long PVA glue will last in modern projects. I wonder if it would last 3500 years. I can't imagine why not.
Fantastic video series!
Wonderful series of videos. Who knew glue could be so interesting, especially given a topic that is basically about "let's watch glue dry". I'd really like to see some real data on how important (or not) it is to put glue on both surfaces. Also as an extension to the current video, how does adding salt (to reduce slippage) impact the strength of the glue joint.
As a beginner fumbling my way through a first project I have to first thank you for this series. This information is invaluable!
I also have a question. Have you ever tested some other ways of filling the gaps? For example, creating a poor man's composite material out of pva glue + cotton, or sawdust? From your test it looks as though the glue's surface tension is trying to create a minimum surface as water is lost, and by adding some fibrous, space-filling material, the shrinkage should be more even and result in a more regularly spaced (and hopefully stronger) lattice.
Once again thanks for the content!
Thanks for the facts. I hope you stick to what You want to test and not get distracted by what others want you to do, which is what they themselves should do.
Excellent video, thanks for making it
I need to see how sawdust/glue mixtures, epoxy, and epoxy/sawdust mixtures stack up now for filling gaps
Thank you for the effort to share this investigation
Really solid research, I tend to use PU glue when I can't properly control for gaps (for example hidden dowels), but how is it for strength compared to PVA?
Your methods are superb and thus provide useful insights, so thank you for taking the trouble to both think through the issues and design appropriate tests.
I wonder if adding saw dust to the glue to varying concentrations impact the joint strength?
Thought this myself. At some point it moves into fiber composite instead of just glue.
@@quintessenceSL oh, well, labels...its just adding sawdust to wood glue. You probably came to that idea too thinking about the voids quintessenceSL?
@@MiniLuv-1984 Yea, if the apparent cause of weakness in a joint is water evaporation, well try to reduce the amount of glue in the joint.
You can do that with perfectly mated surfaces, or you could use a matrix. And no one says it has to be specifically sawdust.
I note from wiki wood has 10% or more water absorption, while FRC is 0.3% and below. While nicely mated surfaces is doable once you have some skill, until you reach that point, here's another option that might actually be stronger and more forgiving.
Extremely useful. Thanks taking the great effort that has gone into making these videos.
Completely intriguing!
love to see you testing gluing green or fresh cut wood
Another very instructive video, thanks again !
Amazing info! Thank you and please keep going!
I really enjoy your investigations. If pushing the limits (model airplanes, speed boats, portable cases, etc.) this is incredibly important. But, for most woodworking projects you aren't trying to minimize weight or size - often a design is "beefy" or "chunky" on purpose, and in these situations sloppy joints are still strong enough for any forces the joint will experience in normal use. If a gap is glue's Achilles heel, suface area is glue's secret weapon. If your joints are sloppy keep going!
Pretty interesting results. Thanks.
This was a really good video and it was devastating to see the difference in 0,5mm gaps. I would also like to see what could be done with different kinds of glues, even if they ”should” not be used in woodworking.
"Precision of a Swiss watch" Shows an American watch.
I rather suspect your 'crazy shop science' will set new standards.
Excellent material, as always.
Excellent content and presentation, as always. I wonder what improvement could be made on one of the test joints if the glue was bulked up with sawdust, for those occasions when the joint is a real disaster, and you need to rescue it fast? That might be a useful follow up to this experiment.
I have another tip for you- cocktail sticks. You can drill out the right size hole and glue them in like miniature dowels. It's another way to fix something that is breaking over time without breaking it apart. You'd think they wouldn't be that strong, but with pva glue and due to the forces being over a small part of the cocktail sticks and the grain being the right way, they are pretty strong.
It obviously has certain best use cases - tension forces, where a tac or nail won't help. A joint that comes loose can be held tight again - its a repair tip really. however it is also very discrete and professional looking.
You can also experiment with paper/card just as well as sawdust if it more suits the application, as you can pressure paper in to a crevice which you cannot do with sawdust pva mix. I'm not sure if that is actually stronger at all, and you have to chose between sawdust, paper and a wedge of wood or popsicle stick depending on the size of the gap. Alas, that is what Mr Sullivan is here for.
Another excellent video. Thanks!
Firstly, I've read many of the comments below and I'm impressed by how constructive and inquisitive they are! These are questions that we have all pondered in one way or another, but never really answered. Brilliant information, thank you so much, you have convinced me to use screws in future, LOL only joking.
Very useful and appreciated. Perhaps dowels and/or pocket screws would provide a joint of preferable strength so long as they were usable on a given project. My limited experience suggests that properly installed dowels should have very small gaps between the dowel and the board in which it is installed providing optimal glue surfaces.
Great work!
It should make all woodworkers stop and think when they use glue.
Thank you
Pretty interesting results indeed, Patrick! Thanks a lot! 😃
What about the salt trick? I wonder if it affects the glue up.
Anyway, stay safe there with your family! 🖖😊
Salt is soluble and very probably would dissolve in the water that is part of the glue.
@@theeddorian I agree, but I've never seen it tested.
@@MCsCreations I agree it would be an interesting test. It's just fun to think about it. The alternative would that the salt could act like debris in the joint.
Thank you for the insightful video as always.
Dr. Sullivan, would you be able to comment about the safety of the PVA glues as an internal medicine practitioner? I know titebond II and III are FDA approved for indirect food contact. However, I would like to know the science behind that more in detail.
Awesome. Thank you for doing this!
Thanks.
I've always wondered if glue needs to be applied to both sides of a joint and if lightly dampening the wood before applying the glue would increase joint strength?
I have heard epoxy is better to use than PVA if you have gaps. I'd love to see you test that addage. Please keep up the good work.
Your excellent work seems to indicate that clamping really is key. It makes me think that joints should be clamped as tight as possible and left in place until the glue has fully cured. Maybe clamp-time vs joint-strength is worth testing.
It is common knowledge to retighten clamps after about five minutes when butt jointing
Another GREAT video!! Two questions: Your initial chart, based on something that has 100% strength, does not indicate when it reaches 100%??? And, your summary discussion of filling the joint gap with a shim begs the question: What if you added sawdust to the glue, to create a sponge-like area for the glue to bind to?
Hi Patrick. This is another great video. I understand that this is not part of the "glue science" so it isn't necessarily applicable here. I'd like to see a strength comparison between a gap filled with wood vs one filled with a gap-filling epoxy.
Excellent and captivating videos. Question... What if you have a sloppy 1.5mm joint, and fill it with a mixture of glue and sawdust?
There is a trick to recovering a loose joint. Dry fit, and mark the gaps. If it's a mortise and tenon, and you've over planed the cheeks of the tenon, check to see where the lost thickness is. If it is symmetric, all to the good. If not, things get fussier. Spread PVA on the cheek of concern, and then press paper on to it. Regular white bond is fine. You don't need or want a polished finish. Cover that with either a piece parchment paper or some other material that the glue won't adhere to. You can think of this as paper shimming, with the paper as bulk that excludes excess glue. Let it dry thoroughly - at least 24 hours, 48 or more is better. Check the fit, correct as needed (it won't be as easy as cleaning up clean wood), and glue up the joint. I started thinking about this while dissecting a Victorian mortise and tenon joint that had paper glued in with hide glue. I have also seen this on shoulder correction.
I am quite sure that adding a shim of veneer works to boost the joint strength of a loosely fitted joint. The question of what other materials also work remains open in my mind. Many people use sawdust, and claim it works. This is harder for me to test in a rigorous way. However, your concept that paper will also do the job is intriguing. I have not tested this, but my hunch is that filling the loose space with paper is probably much better than trying to fill the space with glue. Thanks for the tip.