Regardless of how and when we learned about glues and their relationships with appropriate uses - as craftsmen and -Women, we are always in the learning curve.
I always tell my clients and my students that we are always learning - we're all in the learning curve - it's just that some of us have been in the curve longer than others.
I recently performed a field inspection on a building where a panel of granite literally fell off a building where it had been installed for the last 8+ years. The panel fell from a height of 25 feet, and thankfully, no persons were injured and no property was damaged. In fact, the panel that fell remained intact after it hit the ground - probably because it landed in a soft bed of mulch!
I was contracted by the building owner to visually inspect the piece that fell and the area on the building where the panel had been attached, and provide an opinion on why it fell off. The findings of my inspection were pretty startling, and all the while I was on this inspection, I thought to myself, "This will make a great teachable moment for the readership of the Slippery Rock Gazette."
The details of the project were as follows:
1. The installation was over 8 years old with no previous history of panels falling or changing position from their initial installation point.
2. The stone panels were on all four sides of the building, with the bottom course of the panels starting at a height of 25 feet above grade.
3. The panels were 3CM thick.
4. The panel that fell was attached using a "liner" on the back that had appeared to have been glued on and re-enforced with steel pins (per Marble Institute of America specifications).
5. The original contractor that did the work is now "out of business."
Upon initial examination, the panel that had fallen off the building clearly had glue left on the back of the panel, which was very pliable and easy to peal off of the back. There were two holes where it appeared that pin holes had been drilled, but with no steel protruding from the holes.
The liner was still on the building, held in place by the steel mounting angle that had been bolted to the building structure. There were latent glue remnants on the liner as well. There were two corresponding holes that had been drilled in the liner, that matched up with the interval and spacing that was evident on the panel that fell.
What was puzzling was that the steel pins that were visible on the liner attracted a magnet that I used to initially determine if the steel was "carbon steel" or "stainless steel" (stainless having been specified by the architect on this project in accordance with MIA specs).
Going back to the glue, I was able to peal off a large chunk of glue that was roughly 1/16 thick. It was soft and pliable, almost like a piece of rubber. This did not sit well with me, as I know that on an exterior application using liners - only epoxy should be used!
Furthermore, if you've ever had to remove a piece of stone that has been glued properly using epoxy, the stone will fail before the glue will. In my experience, properly cured epoxy does not just "peel off" when it's pulled with little or no effort.
This thought brought back memories of talking with Mike Beckmann of Touchstone/ Bonstone, and James Ogelsby of Tenax - who both have re-enforced this concept. I had always though (mistakenly) that epoxy is used on granite, and polyester is used on marble and limestone. This is not the case.
Whenever you are doing an exterior application using vertical stone, epoxy glues are the only glues you should be using. Polyester is not acceptable for an outside application.
I use this analogy to explain the difference:
Epoxy soaks into the stone, while polyester sits on the stone. Using the stain versus Silly Putty analogy, cup one hand and pour some Minwax Ipswitch Pine wood stain into your hand and hold it there for one minute. After one minute, dump the stain out of your hand and see that the stain "soaked in" to your skin. This is how epoxy bonds to the stone. It fuses with the crystal structure and becomes part of the stone.
Now, take a hunk of Silly Putty in your other hand, squeeze it tight for one minute, then release. When you open your hand, you'll see the "imprint" of all of your fingerprints on the Silly Putty, but there's no Silly Putty residue stuck to your skin. This is how polyester works - it does not fuse with the stone crystals.
After close examination of the two stone panels in question, it is my opinion that either the glue used to attach the liner to the back of the panel was defective, or it was polyester. Epoxy glue had been specified as the only glue allowed to be used on the project. Without testing a sample of the glue, I will not know for sure, but the following reasons are possible based on what I observed:
Prime suspect: the glue used was polyester. If the glue was epoxy, the following reasons for its failure could be that:
a. The components (hardener and resin) were mixed in the wrong ratio.
b. The glue did not cure properly.
c. The glue components had possibly expired prior to use.
d. The glue components had broken down due to excessive heat exposure.
I should also mention that freeze /thaw cycles probably played some portion of a role in this failure, as the panel that fell was on the east wall of the building, getting a daily does of morning sun that "topped out" (temperature wise) at 150 degrees. The working limitation of most polyester is 140Fahrenheit.
Furthermore, the steel pins that were used as a mechanical safeguard were not stainless steel, but rather, cold carbon steel that had probably corroded over 8 years of water exposure. I made this conclusion after examining the caulk joint above the piece that fell. It was totally devoid of caulk along 24 running inches of seam which certainly would have allowed moisture to penetrate behind the panels, allowing condensation to affect the carbon steel pins, and eventually resulting in their deterioration and eventual failure. This alone would have caused the panel to release from the building and fall like a 100-pound Guillotine blade.
The bottom line here is that had the original contractor used epoxy glue and stainless steel pins, I would not be sharing this case study with all of you. It just goes to show that there's a right glue for every job. Using the Marble Institute of America's Design Manual (the latest version 7.2 is now available) and asking for the right glue for your job from the knowledgeable guys at Braxton-Bragg, will keep you in the clear every time.
Until next month...
Best Regards & Happy Fabricating! "Right Glues for the Right Job" is a "handson" topic that is taught each month by Kevin M. Padden at the AZ School of Rock in Gilbert, Arizona. Log on for more information at www.azschoolofrock.com . For current class schedules, contact Kevin at 480-309-9422.
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