How strong is JB weld structural epoxy adhesive anyways ? Destructive test, simulation and review

JB Weld Original Cold-Weld 8265-SUK Steel Reinforced Epoxy (5020 psi)
I did some science to destructively test a join made using JB weld to see just how strong structurally adhesives are vs their claims. Interesting results.

[sidneydawe]

There is a letter (not le--er) T in the alphabet. Please use it instead of the glottel stop. It's no wonder that Americans cannot understand the British (or is it Bri-ish) way of speech.

[danroberts]

This is a true story: Way back when I was about 18 years old (around 1978 or so) I worked as a mechanic in a small (tin shed) mechanic shop. Most of our customers were lower income and we were always having to find ways to fix their cars on the cheap. Well, one day, this old man drove his old truck in with a water leak. I climbed up under it to see what the problem was and low and behold, he had a huge crack in the side of the engine block. If you added water, it just poured out the side. Clearly he needed a new engine. But sadly he didn't have two dimes to rub together. So I suggested to my boss that I try cleaning it up real good and putting some JB Weld on the crack. We figured nothing from nothing leaves nothing (that song just happened to be playing on the radio at the time) and we didn't see how it could make it worse. So I did. Well sir, believe it or not, it worked. For years we'd see that old man driving his old truck all over town with a free JB Weld repair. Yeah, we didn't charge him for the fix. You never know when you'll need some good Karma.

[hughacosta]

JB Weld is incredible. While active duty in the air force, we used EpiSeal 20/20 for recovery of damaged aircraft when time was a constraint. We applied a thin coat of the adhesive to each face and then laid a piece of cheesecloth over the adhesive. Worked the 20/20 through the cloth and then stuck the parts together with clamps. The cheesecloth maintained a thin bondline between the metal and never failed us.

[kenji-xjft]

Went on a camping trip and while towing my camper, my radiator reservoir cracked and caused my car to overheat and my whole car would steam up. Radiator fluid leaked all over. Where I was camping at was 45min deep into the forest. Thankfully, I always prepared myself with a good toolbox with essential needs. I happened to have my plastic welding tool and hooked it up to my generator and spent some time welding the large crack. I made sure it was good and sealed and sanded it down a bit so the surface can bond better. Then I busted out the JB weld and pasted it all over the crack for extra reinforcement, i made sure the surface was clean and debri free. Its been 12 years and this thing still holds up like a champ.

[richardsandwell]

Fascinating work, I will never scoff at Epoxy again, I know it cannot replace welding in a lot of cases, but it is nice to know another alternative.

[windward]

For Automotive structural joints, often the choice is between a welded or a bonded (using adhesives) joint. However, with the adhesive joint there is usually a preload clamping device in place while the adhesives cure, many times rivets are used (sometimes spot welds), where they remain and are not removed.

From a design standpoint we have different unknowns which factor into the quality (strength) of the joint in how it is loaded. With aluminum welding can reduce the maximum tensile strength in the welded zone (heat effected zone), but there are many variables as to the magnitude of this reduced strength such that the joint safety factor is increased to compensate. This can add weight, which is not beneficial in weight sensitive applications.

The interesting thing with your demonstration is how the adhesive fails. The shear is not transmitted to any fastener, because there are none. But if there was a preload device than shear never would be transmitted to the clamping device, because the failure mode strength of the adhesive is so much greater than the preload the force, the fastener would just be overwhelm during failure. In other words, the failure mode is catastrophic and without warning, except of course for the cracking sound before the joint explodes.

The better test would be for shear fatigue, because the joint surface area is so much greater with adhesives. So what would be the fatigue life loading and cycles between a common two row riveted lap joint one without adhesive and one with keeping everything else the same?

As you mentioned the applications of adhesives are confines to relatively low temperatures as comparted to a welded joint. Although metals also exhibit a reduction in strength with temperature but at much higher temperatures as compared to adhesives.

[randydewees]

My first real encounter with metal filled epoxy was in 1982 when on the road with my friend in his Datsun 510 (the "Rotsun"), my dad recused us by providing us with some Devcon product to repair a leaky radiator. He warned "you get that to a radiator shop ASAP". Turned out Jim never did any further repair, and sold the heap on several years later.

Many a dirtbike has had engine cases put back together with JB Weld. I did this with my daughter's Honda she flicked into a boulder pile. Well I remember her thinking she'd killed it for good - hot oil on the rocks. We carefully collected all the pieces and that night I put Humpty Dumpty back together again.

BTW, I've had very good results with "G-Flex" toughened epoxy for bonding various plastics. These joints need to be flexible and strong, if not as strong as the components. I use a variety of fillers, lately I tried the powdered PMMA that is used for artificial nails (!). I like it.

[GaryL]

The bonding strength can be improved somewhat by "roughing" the surfaces with an abrasive wheel. I use a 3M Paint and Rust Stripper abrasive wheel for gluing metals. I find JB Weld quite good.

[jackmclane]

Awesome testing! I love it! It is - after all - still a type of glue. And glue has certain properties that make it excel in one load type and pretty much suck an another.
All glues love shear forces. All glues hate tension. And worst of all: Peeling tendencies that combine tension with a stress riser. It is the task of the designer, to enable the first and prevent the latter. Your test is primarily shearing. The side pipes turn a little but then carry all the load on the inner edge. This is why you hardly see any peeling. If they were longer and would bend and turn under load, the peeling action would be much more pronounced.

[dennyliegerot]

Yep...JB Weld is amazing stuff. I've used it for years repairing motorcycle cases, radiators, etc. Use common sense and prep surface well. It's not great for all applications but will usually get you by in a pinch until you have time for a proper repair. Although I repaired a leak in a KTM radiator 23 years ago and still perfect even with all the heat cycles.

[stihlRoush]

It would be cool to see the same test with the same set up, welded together as a direct comparison!

[zzzsydneyhom]

Thanks for the excellent Demo mate.
About five years ago I did a "temporary" repair on the exhaust manifold on my yacht's diesel engine with JB Weld.
The stresses on the repair site were vibrational and extreme heat mostly and I have to say that JB Weld amazed me to the point that I am still waiting for it to fail.

[lohikarhu]

I found that JB Weld seemed to outperform pretty much every other epoxy that I've tried... and. of course, the fast-cure ones are pretty much 'plastic'... and, indeed, certain materials just don't 'wet' well, and are rather hard to get together.
I had quite the argument, about 30 years ago, about adhesives, versus welding, for assembling a large opto-mechanical system, and I was convinced that the large wetted area of a tube mounted to a curved surface, would give large enough retention, without all of the issues that welding make for distortion and retained stress... sigh. But, even at that time, adhesives were being used for precision optics, using 'cure-in-place for accurate alignment/centration, and reduced cost.
Great video!

[davidsnyder]

Love this test and what a great job you did with filming everything. This test you came up with is very impressive 👍🙂

[hando]

Came for the Tie Fighter, stayed for the glory of epoxy. Thank you for the demonstration, explanation and factor diagnosis. Great video!

[andyb]

Very impressive test, I would never have guessed that JB Weld would hold that well. Thank you.

[justinkase]

JB Weld is always impressive in my experience. It will not do EVERYTHING a weld could do, but it's still very versatile. I have even had the putty perform well, but mainly used that in compression and put screws through it.

[joescheller]

Had very good service using JB weld never failed me yet. Had a farmer friend repair an injection pump for diesel had cracked housing. Used JB to glue it together and its still running 20 years later

[donneff]

Cool video. I particularly like how you detail each step so another person could reproduce the results, if desired. Thanks

[RonBaker]

JB is one of a kind. I have made several fixes with it on many different materials over the years and only the ones in vehicles eventually failed. If it isn't subject to vibration it holds forever.