gluing rock?

[Biomorph]

I saw in the NY Times a few days ago notes of an interview with Mitt Romney, Governor of Massachusetts, discussing the tunnel ceiling collapse in the Big Dig in Boston. He noted that the epoxy holding hundreds of ceiling bolts had failed--whether a systemic failure or a "bad batch" was, and is still, not clear. What was most interesting was his comment that maybe the connections should have been made with some sort of an expansion into the rock or should have been welded--he said soldered--to the steel tunnel supports.
I go back to when it seemed that all good connections were deemed to require a mechanical basis and even now cannot escape some uneasiness with any glued joint---no matter how convenient and no matter how advanced the dope. There was a reason for the old way. Ask Mitt.

[Rick Clise]

Hiya Biomorph, You opened-up an interesting topic about trusting mechanical over adhesive joints.

I was the 'designated' welder for our daughter's school's 'Pedal Prix' team - making a human powered racing tricycle for a 24 hour long race last year. We made the trike out of 4130 chrome moly tubing, with tubing from .25" to 1.5" in diameter, with wall thicknesses of 0.9mm (0.039"?) and 1.2mm wall thickness, all TIG welded together. The tiny welded joints were stronger than the adjacent tubing as some of the others on the contruction team found when trying to break a weld and the tubing tore while the joint remained solid.

To save weight in some non-structural areas we used aluminium (aluminum in the USA) tubing over chrome moly spigots as bracing, using an industrial two part adhesive to glue the parts together. There was significant resistance in the team to doing this - most of the guys 'just didn't trust' gluing two metals together. It worked fine in our application where there was sufficient glue in the joints, and the potential for catastrophe in our situation was certainly much less than a tunnel collapsing. But the human nature in our team was to stick with a mechanical joint over glue.

Good thing they didn't read the article you referred to!

Regards, Rick Clise

[EJB]

Any time I use an adhesive, I operate under the assumption that it will fail in my lifetime. Whenever possible, a mechanical connection is preferred. That way you can assemble and disassemble at will. Very helpful if you are of the CONSTRUCTIVIST persuasion. Murphy's law tends to dictate here when the 'permanent' sculpture falls apart and the one needing to be removed won't let go. Of course if you apply your adhesives properly, thoroughly and double check it every step of the way I guess there is no question it will work, like they do on the Space Shuttle.
....oh, never mind.

[allenring]

It is like every thing else their is an application for gluing and one for mechanical joints. Glue two pieces of pine together with wood glue, Tightbond form Home Depo etc. being better than Elmer's, and the joint is stronger than the wood. You can demonstrate this by breaking the pieces and watching the joint still hold.

The material they use to glue anchors is stronger than cement. All kinds of things could have failed other than the bonding material. And yeah, even rocket scientists 'blow' it occasionally. They glue the heat tiles to the space shuttle. The glue does not fail, the crummy very brittle ceramic tiles are what fail.

I am a great fan of adhesive. I glue aluminum to aluminum and stainless steel to itself, never had a failure even in wet hot environments. Just got to get the right stuff and know what you are gluing too. An over the top, glue truck bodies , air plains, and aluminum to brick adhesive is called Depend 330 by 3M. It sets up in 30 seconds, neat eh. You can get the stuff from MSC 800.645.7270. I started a thread on MSC, great company.

[fused]

There are definitely some amazing adhesives out there and I have a lot of confidence in the ones that I use. It might be interesting to know what went wrong with the tragic collapse of the tunnel in Boston... if it is ever definitively concluded how the ceiling actually failed.

Of course there are exclusions to eveything and having said "I have a lot of confidence in the ones that I use" in reference to adhesives, I just attached an Asian stone carving to a steel base. The carving is an alabaster/soapstone with a hollowed out bottom and I filled that cavity with PC-7, a long setting two part epoxy. Because of the type of stone I didn't trust this epoxy and stone combo and set two anchors into the bottom of the carving before the epoxy fill and then screwed the steel to the hardened epoxy.

[Rick Clise]

For some applications where I need to attach two bits of steel together but may need to remove them later, like attaching a coverplate to a sculpture base, I've been using silicon adhesive. When it needs to be removed later I can use a box cutter blade to slice the silicon apart.

I haven't used silicon for structural connections.

Rick

[allenring]

You may be surprised to know how often silicon is used structurally. That big wash sink in your local Starbucks; silicolned on to the flake board sub-straight. Their are all kinds of metal panels, bank fronts, elevator surrounds, that are hung using silicon. But use silicon around you tub for caulking and it will fail every time. This mistake is made over and over.

Silicon sticks extremely well to stainless, glass, ceramic and so on. Because it stays flexible it allows for expansion between two different materials. But it needs to be applied between two things. It is no good on the surface of something, especially if it is a tub that already has a soap film to prevent adhesion.

To Fused, the PC-7 fan consider trying Devcon, a two part epoxy putty, comes in an under water, plastic,aluminum, steel, titanium, ceramic and bronze compatible version. You will not need any anchors. Again, call MSC 800.645.7270