Glue Myths

Has anyone seen Glue Myths by Patrick Sullivan: Glue Myths: 1. End grain - YouTube

I just finished watching it after reading your post.

Not surprising. I've gotten away with that "wrong" practice many times over the years. On one occasion while knocking together a couple saw horses from scrap I realized at the last moment that there wasn't a piece long enough for the second top rail.

In desperation, I made fresh square cuts on the ends of two shorter pieces and glued them, figuring I'd later "splint" the joint with another piece of wood. When it cured it was so strong I decided to just try using it.

I've also broken the rule of not gluing cross-grain joints. Years ago when I needed to pre-stain a bunch of long deck boards in a small indoor space during bad weather I cobbled up a multi tier drying rack from 1 x 3 pine strapping. I just placed the horizontal pieces at the appropriate spots on the verticals using a blob of glue and 2 18 gauge brad nails. The nails alone were too small to support the load. When I was finished with the deck I thought I would just break the rack up at the "weak" joints. Big surprise! It was so much stronger than I thought I ended up using a Sawzall to dismantle it.

Since those 2 experiences I've done it "wrong" many times since. I've even glued end grain joints on the bottom of legs to be used outdoors using small pieces of more rot resistant wood where it sits on the ground. I wouldn't do this however where there would be much side force on the legs.

WOW! Who would have guessed. I would like to see the same tests using epoxy and also finger joints.


Tom

I have done destructive testing on epoxied finger joints (not as accurate as Sullivan’s) and they weren’t as strong as I expected but epoxy sure makes the assembly easy.

Here is a great YouTube response to Sullivan’s glue tests: End Grain Glue Myths | You May Have Misunderstood - YouTube

What he proves is that side grain wood breaks before the glue joint. (Something we already knew.) Not that you can substitute end grain butt joints for one continuous length of wood. The end to end is not stronger than a continuous piece of wood. He also ignores movement of wood over time and its effect on the strength of the joint.

He says numerous times in his video that long continuous grain is always much stronger than a glue joint

He rediscovered gravity.

And he’s probably a smart, competent, nice person. But the video is pretty much just click bait. Well produced and presented click bait that knocks a strawman right on its ass.

No real demonstration.

Nothing new either.

Picked up a woodworking mag maybe 20 years ago that did similarbut did it correctly

They made assorted connections and placed them I a press and measured the failure point.

Final point was dowells and brisket do not add any additional strength, surface area does.

Mechanical holding adds too.

Dowels and biscuits do aid in alignment and fixture and maybe in corners of picture frames but for basic joinery good glue, proper joint and the wood fails before the joint.

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People often seem to class strength as the main consideration- but tackiness , and lubrication are also important. I have assembled joints with rub fitted titebond, and others with polyurethane, neither of which would have been suited to the other glue. The slipperiness of urethane can be a real asset in a big, tightly fitted joint.

Yes! I like the lubrication quality of polyurethane glue, haven't used it for years mostly because of the shorter working time - maybe that's changed?

Lanso said:

Yes! I like the lubrication quality of polyurethane glue, haven't used it for years mostly because of the shorter working time - maybe that's changed?

Click to expand...

Not sure, it may depend on moisture in the wood- it has saved my butt on some big tight tenons though- the kind of thing you know is just waiting to stick solid with a water base glue.

Yes, the working time of poly glue has changed. There are now options available and you can go from the fast setting (15 minute) to up to 60 minutes of working time. Several companies are offering poly glue with the choice of open time.
I often use poly glue for veneering and the 60 minute stuff is great for larger glue ups, no panic point and a nice easy relaxed glue up.

Interesting! I've used polyurethane (Gorilla) to glue together thin strips of ebony and satinwood to be boiled and bent, or to repair cracks in stock to be steam bent. It's ability to withstand heat and moisture are great qualities.

But it always seemed to have a bad reputation because of the foaming and messy cleanup, so I avoided it otherwise. For large or complicated glue ups I used urea resin - plenty of time and low tack. For veneering large panels in a big screw press I liked epoxy - even more time, no moisture added, and works in cooler temps.

So Michael, am I missing something?

Richard,
I don’t think you are missing anything. There are lots of option for veneer pressing glues. I needed to glue some veneers to a steel substrate and after some testing I found the poly glue worked very well. The biggest problem with poly glue with larger surfaces is the spreading of it evenly. Even the Kliebert I use is still pretty thick but much less than the gorilla brand. So I made up my own roller from a small paint roller and a piece of radiator hose. The rad hose is soft enough to be pliable and I found a size that slips tightly over a heavy nap paint roller. So I ended up with about a 2-1/2” diameter x 4” long roller that is easy to replace as I thought I might have to replace often. So far I am still using the first one I made. The glue spreads really nicely with this roll and I roll it over some paper after I am done and let it dry right on the roll, then use it again with no problems.
The advantages are a one part glue with no smell, very little or no bleed through and it cures very quickly. It is a little bit temp sensitive so on a hot day you will have less time. It is not a ridgid bond so not good for bent laminations but any flat panel work is fine. The only real problem is getting the glue on your hands so I usually wear gloves.
I did a number of projects with the standard poly glue and now that there is a choice of open time it is even better for veneer panels.

Here is an interesting video about endgrain gluing.

A misunderstanding of the end-grain glue "myth" video? - YouTube

Dave

Good video - he is articulate and polite which made it a pleasure to watch.