Glue Failure? How likely?

If glued correctly….that is, if your glue joint is no bigger than 5 thou it should never fail. Like you said, the glue is stronger than the wood itself….if done correctly. If the joint is sloppy and you try to accommodate this by using more glue to “fill” the gap. Then yes, there will eventually be glue joint failure.

-- Childress Woodworks

Most of the additional mechanical fastening was done before the advent of the modern woodworking glues,they are used now because we like how they look or to show-off. If you are expecting (hoping) a piece to last 100 years or more then some kind of fastener is a good idea.

Regards
Jerry

-- jerry,mlchigan

I have never had a glue failure, except for the hot glue gun type.

Carpenters glue works great.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN. http://www.woodcarvingillustrated.com/gallery/member.php?uid=3627&protype=1

“How likely is glue to fail?”
Depends….. How well is the piece designed?, How much stress is the joint going to be put under? How much expansion/contraction is the wood likely to endure over the expected lifetime? Do you want the piece to become a familt heirloom? Or is it going to the dorm? Is the wood you’re using oily(teak for one). TitebondII is a great product, but it hasn’t been around 100 years. No one answer is going to cover this question, just as one glue is not the answer for all joints. When I build my lamp shades I use 3 different glues for different joints & I still worry because the thinness of the pieces precludes the stronger designed joints I would prefer to use.

-- http://www.grandprairiewoodworks.com http://www.etsy.com/shop.php?user_id=6453794

I agree with that last statement. the other day I was trying to split a board through a glue line, but the wood failed first…
For a few bucks more, I would upgrade to Titebond III, the “ultimate” thing, it’s the best!
The secret of gluing are Clamps, the more you use, the better, the thinner the glue layer, the stronger results.

-- Francisco Luna, San Francisco Bay Area.

Tim has said it well.
I disagree with you Moai regarding “the thinner the glue layer, the stronger results”
I think you can overtighten your clamps squeezing out too much glue. A nice thick bead of glue will soak further into the wood giving you more strength than a thin film on the surface in my opinion.

does anyone know if glue actually weekens the wood next to the joint? Anytime I see a test for glue failure, the break is always right next to the glue. I’m wondering if the curing process somehow stresses the wood fibers and weekens it.

From what I have read you only need glue coverage thickness in the 1-2 mm range for proper adhesion. You can over tighten the clamps and squeeze out the glue. A Fine Woodworking article on glue ups had a great tip..tighten the clamps with your off hand as tight as you can, that is ..if your right handed tighten the clamps with your left hand as tight as you can. The only failure I have ever seen on a glue up is when your trying to glue end grain to end grain. Aside from that the wood will fail before the glue joint will if done properly.

-- David, South Windsor, CT "I love the smell of sawdust in the morning"

glue failure is very unlikey… wood will fail first – IF the glued edges are long-grain to long-grain…

if it’s end-grain to end-grain or end-grain to long-grain, then the glue might fail, but thats where joinery comes to play. one of the benefits of using M&T, dovetails, and box joints is that they introduce long-grain to long-grain in a situation where otherwise it would be long-grain to end-grain thus creating a strong glue platform.

-- When in doubt - There is no doubt - Go the safer route.

HokieMojo – the reason you see the wood fail NEXT to the glue joint is not because the glue weakens the wood there, but because the tests that are run, are focusing the tension/pressure on the glue joint itself so thats where the force is applied… since the glue joint is stronger than the wood, the wood that is closest to the location where the force is applied is the one that breaks- read- the wood next to the glue joint (closest wood to where the force is applied)

-- When in doubt - There is no doubt - Go the safer route.

Excellent advice. Thanks so much.

Reason i’m asking is that a friend has asked for a trunk that she will be actually using for travel and I’m worried about the glue joints being exposed to abuse.

I understand the more long grain contact the better and that end grain really doesn’t adhere.

Fasteners are still an option and I think I might use some nice contrasting plugs for that end.

I have used Titebond III for some time, but the cost difference (they are next to each other on the shelf, what better comparison can you make?) is what has driven me to use Titebond II most recently.

I’ll trust the glue joint and add some fasteners where I think appropriate, now if I could only find hardware that I like…

Cheers,
Ivan

-- Someone once said "There's nothing you can't do, just stuff you haven't done yet". I like that.

if the joint is tight.. not so tight that it does not leave room for glue, and the wood is fresh sanded or milled. 40 plus years, zero glue failure..

-- It's not a sickness, i can stop buying tools anytime.

PurpLev,
That makes sense. Maybe I’ll try to confirm someday by gluing a 4 inch board to and 8 inch board and seeing where the split happens when presure is put right in the middle. Then again, it might just test how bad my glue joints are. thanks.

I just finished reading an old Fine Woodworking article (11/1987) ‘Coping with Failing Joints’ by Bob Flexner. If any of you have that issue it is worth reading. The part that stuck in my mind was Bob’s statement ‘There is, In short, no known way to bond wood together in cross-grain direction and expect it to survive in everyday use for more than 50 to 100 years. Everything we build or repair will come apart sooner or later.’ He also states ‘A woodworker or restorer should pick a glue that can be removed easily and with little damage to the joints, so that the furniture can be reglued effectively in the future. It’s wiser, therefore, to build or repair with future repair in mind than with hopes for permanency.’

-- Ron in Osseo, Minnesota

Using the right glue for the job, and the glue is fresh… it should never fail.

Now if you want to pin for more strength, thats great, especially if you use a contrasting pin to make the joint even more visually interesting.

-- making sawdust....

I read one of the articles on glue strength and was pleased to see that the Poly glue did not fair all that well.

I made a desk with the Gorilla glue and to be honest I didn’t like using it, too much mess and fuss (pre-wet dry surfaces, clamp quickly, etc…) but the desk has not come apart in over 8 years.

I suppose that if I want this to last ‘forever’ I’ll make it out of diamonds. Realistically I’d be thrilled to get 50 years from a piece that will see real use.

Thanks again,
Ivan

-- Someone once said "There's nothing you can't do, just stuff you haven't done yet". I like that.

looking that you’re referring to a piece that will be used as a traveling trunk – I’d also recommend adding some sort of hardware to protect the corners, and act as ‘feet’ for the trunk to rest on, so that the wood is not in direct contact with moist/abrasive platforms (car/floor/cement/etc).

-- When in doubt - There is no doubt - Go the safer route.

Glue failure has to do with a few variables. Sorry if I repeat anything said already. Number 1 is the material. If you use the same tecniques to glue teak as you would alder I’d say you’re obviously in for some trouble. Cleaning the material with mineral spirits will help the gluing process because you get the oils off the material. Teak may require Acetone or the like, and you will need to act quicly as the oils will just come back. Teak was my example. You need to research what oils the material you choose may have, if any.

So there’s the type of material to consider, but also theres clamping preasure. If you don’t use adequate clamping the joint will be weaker. There is a website somewhere that tells you what clamping preasure is adequate for different species.

Then you should consider that gluing long grain to long grain is the best, so lets say using a mortice and tenon for example, the joint will be stronger with a longer tenon, as opposed to a shorter one because there is more long grain to long grain surface area accepting the glue. The thicker the tenon doesn’t really matter because you are widening the end grain aspect, which doesn’t glue well. You are also weakening the amount of material holding the tenon in.

Pinning Mortice and Tenon joinery is really up to the builder. You need a longer tenon in order to pin it, and by creating a longer tenon you are creating more long grain to long grain gluing surface. Thus making the pin somewhat irrelevent and more decorative.

Everything I have said here is based off of my own knowledge and experience. I am in no way an expert on glue, and I may or may not be wrong. For tested results you may research the Glue manufacturers website.
Hope that helped.
Sorry for any miss-spelled words, grammar problems, etc.

-- ~ Inspiring those who inspire me ~

I built these kitchen cabinets in 1974, I don’t think they even had yellow carpenters glue at the time.

If they did, I didn’t know about it.

I glued these with Elmer’s white glue, & they’re still sticking together, good as new.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN. http://www.woodcarvingillustrated.com/gallery/member.php?uid=3627&protype=1

Great job on the cabinets, & I also have stuff glued w/ Elmer’s white glue, most notably 2 tables I built in Jr high shop class in the late ‘50s that are still just fine. We’re talking a half a century & student level skills, so if the new glues are better…one can only imagine…-SST

-- Accuracy is not in your power tool, it's in you

Thanks for the feedback, I feel much better.

Yes I had planned on using osme hardware to protect corners and the bottom, my main concern was with the splined mitre joint at the corner. Perhaps I’ll use some ‘straps’ around the corners to reinforce it further.

Hopefully now I can get down to actually building….

Cheers,
Ivan

-- Someone once said "There's nothing you can't do, just stuff you haven't done yet". I like that.

I have had glue joints fail when glued at very low temperatures (40-50 degrees F). They held for about a year, and then gave up.

I saw an article about a year ago (wish I remembered where) that said it’s basically impossible to “starve” a glue joint by overtightening your clamps. The viscosity of the glue creates friction, so at a certain pressure some of the glue gets “stuck” in the joint and can’t squeeze out.

-- http://www.north40custom.com -- http://north40studios.etsy.com --

Whenever I do a glue up on a rail, & style door, when I apply two coats of glue to the rail end grain.

I leave the first coat soak in for awhile before I apply the second coat.

Maybe that’s why I’ve had success with my gluing.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN. http://www.woodcarvingillustrated.com/gallery/member.php?uid=3627&protype=1

Yes Peter, you are right, but overtightening can starve a joint. The only thing is, you can’t achieve the pressure needed to be “overtight” with hand clamps. Only hydraulic clamps can do this. The key, is to get the glue joint as thin as possible. Moai is right, the thinner the glue line, the stronger the joint. This is correct with our glues today.

-- Childress Woodworks

Here’s a glue joint test from Wood magazine.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN. http://www.woodcarvingillustrated.com/gallery/member.php?uid=3627&protype=1