Frederick M. Hueston, PhD

I had just gotten off the plane, headed to yet another stone inspection –or more precisely, a terrazzo inspection. Well, since terrazzo is made up of stone chips, I guess that counts. 

Just as I was about to head to baggage claim, I heard a loud alarm. At first, I thought it was one of those door alarms, but this sounded a bit different. I kind of ignored it, and the next thing I knew, the overhead sprinklers came on and started spraying water everywhere! Holy crap, I thought, the airport must be on fire!

I started walking faster, hopefully away from the fire. Just as fast as the water started, it stopped. However, I was wet and this was supposed to be a one day trip, so I didn’t bring a change of clothes. Do I buy a change of clothes at the airport and pay a ridiculous price, or do I stop at Walmart or somewhere on my way to inspection? Thrift won that argument, so Walmart it was. After all, a soaking wet man in Walmart would probably be ignored anyway, compared to the sights I’ve seen at Walmart. Little did I know that this little drama would lead me to a clue for the terrazzo inspection I was about to perform.

I made my quick Walmart stop and picked up an outfit. That means underwear, shoes, socks and the works, in case you’re wondering. (Please, no emails asking if it’s boxers or briefs– LOL!) I paid for my purchases, changed in the restroom, and I was off to my inspection.

I took an Uber to the building and noticed a group of people waiting outside as we were pulling up. I got out of the car and the entire group started walking toward me, which was kind of weird. One by one each one greeted me. It was a mixed pack of architects, contractors and lawyers, oh my! This is going to be fun, I thought.  

You could easily tell who the lawyers were. They were the ones in 3-piece suits. The others were in either work uniforms (logo on the shirt) or were dressed professional-casual. One of the lawyers handed me a yellow pad and asked me to sign in. The GC, the one who called me about this project, invited me inside to take a look at the terrazzo floor.  

I walked into a very large lobby. When I say large it had to be over 50,000 square feet! I noticed immediately that the terrazzo was bubbling. The bubbles were all over the place, and ranged from about 1 inch in diameter to over 6 inches. There had to be thousands of them. I took a quick walk around the lobby followed by my posse of lawyers, contractors, etc.. The lawyers were hanging on to every word I said, and appeared to be taking notes.

 Fortunately, I have been in this situation before, and the only verbal responses they got out of me were my questions. I learned a long time ago not to speculate or come to any premature conclusions. If I did, it would surely come up later in a deposition, or even in trial. 

My questions were straight forward. Here are a few examples:

How old was the installation?

When did you notice the bubbling?

Were there any installation specifications?

Was the slab tested for relative humidity before installation?

Have any tests such as core samples or lab tests been performed? If so, I would like to see them.

And so on…

Now, for those of you not familiar with this bizarre bubbling terrazzo condition, this was a classic case of osmotic pressure caused by moisture in or below the slab. This was an epoxy terrazzo installation. Epoxy is not porous and will not allow vapor to escape. If the terrazzo was Portland-based it would not bubble.  Of course, I didn’t divulge this information to the pack.

I had to try and find out where the moisture was coming from, which led to even more questions:

Was there a vapor barrier under the slab?

Did they use a membrane on top of the slab?

Was the terrazzo poured before the building had a roof on it?  (If it had rained, the slab could have been soaked.)

What type of soil is under the slab?

Was there any event like a flood or hurricane that could have soaked the slab?

 No one seemed to have any answers, so I would have to dig deeper.  I asked if anyone had any questions and they all stood there looking at one another. One of the lawyers asked me if I had any idea. I told him I would have to do some more investigating before I could reach any conclusions. I told them I was going to walk around a little more before I caught an Uber back to the airport.  Fortunately, they all left and I continued my inspection in peace and quiet. 

I walked again to the end of the lobby and noticed a lady mopping the floor. I walked up to her and started a friendly conversation. She asked me if I was here for the floor.  I told her yes. She told me that she was actually on the construction crew and witnessed the floor going in, day after day. I let her talk and then I asked her if she noticed anything unusual before or during the terrazzo installation. She told me that the day the terrazzo was supposed to start they were testing the fire system and the sprinklers went off and soaked the floor. BINGO, I thought. From the experience I just had at the airport, I was quite aware of how much water can end up on the floor. I asked her how long the system was on. She told me for over an hour.  At this point, I thought I had my answer for the bubbling. Of course, I would have to follow up with some core samples and lab tests. But my gut feeling was the slab was soaked and was never allowed to dry.  As it turns out, the contractors and lawyers were looking at the wrong parameters for this condition. They didn’t have the lab test for moisture, so of course the results came back “normal.” So, as it turns out, my hunch was right.  Sometimes it’s a matter of asking the right people the right questions. Another case solved. 


The Stone Detective is a fictional character created by Dr. Frederick M. Hueston, PhD, written to entertain and educate. Dr. Fred has written over 33 books on stone and tile installations, fabrication and restoration and also serves as an expert for many legal cases across the world. Fred has also been writing for the
Slippery Rock for over 20 years. Send your comments to .