Slippery Rock Gazette

Frederick M. Hueston, PhD

I was having lunch at one of those family-style restaurants – the ones where you sit around the table with strangers and they bring the food out in big bowls. It was kind of interesting meeting new people, but there was this one gentleman who keep asking me to please pass the salt – like I was the salt keeper or something. It was a little annoying, however, his persistence would help me solve another stone installation mystery. 

I had just finished my lunch and said my farewells to my new dinner table companions when my cell phone rang, and I answered it as I headed out the door. The lady on the other end was crying and a little hard to understand. I thought I heard her say either something to the effect of “I’m going to bed,” or “I’m going to be dead.”  What she was trying to tell me was that “she was going to be dead if she didn’t solve this problem.”

 I got her to calm down so she could explain the problem. She said she was a designer who just completed a large home on an island in the Bahamas. It was apparently some celebrity’s home. She wouldn’t or couldn’t tell me who. She told me they installed a ton of French limestone around the pool and walkways and it was beginning to flake and fall apart.  She actually wanted me to fly there the next day to figure out what was going on.  Well, who was I to argue with a trip to the islands? So, I told her I would catch a flight the next morning and investigate. She said she couldn’t be there, but the housekeeper would let me in.

I caught a small puddle-jumper to the Bahamas. I got off the plane and was immediately greeted by a tall Bahamian gentleman holding a sign with my name on it. I was thinking of renting a car, but this was better. They drive on the opposite side of the road – which I have done before – but it takes some getting used to. I was planning to use the travel time to the house recuperating from my bumpy flight.

I hopped in the small Jeep and off we went. My chauffeur drove like he was a New York City cab driver! I was now hoping we didn’t have to go far! Mercifully, we soon pulled into a gated community, and in front of us was this large house. I mean it was so large, it looked more like a hotel.  

We pulled up to the entrance and the housekeeper was waiting for me on the front porch. She didn’t say a word and just led me to the back garden and pointed toward the pool. I turned around to thank her, but she was gone. Wow, I thought, how rude was that! 

Spalling and not spalling limestone, side by side. There’s a clue here…

I walked over to the pool deck and noticed right away that the coping around the pool had a spalled halo along the outside of the stone – and not the side near the water, which was what I was expecting. I also noted that there were French limestone pavers adjacent to the coping that looked fine (see photo). Of course, there was no one around to answer any questions, so I decided to figure this out from the available clues.

To make a long story short, I discovered that the coping around the pool was set in a standard setting mortar. The stone on the deck was set in sand. I placed some water on both stones and noticed that the coping beaded up the water, and the sand-set stones did not. This told me that the coping was sealed and the other stone was not. 

So why was the stone spalling only on the outside perimeter of the coping stone?  I sat there for several minutes trying to figure it out. Of course, that was difficult, cause it was right on the ocean, and I kept wishing I was sitting on the beach. Then all of a sudden, it hit me like a ton of bricks. As I was looking at the ocean I thought maybe the salt water was affecting the stone somehow, but that didn’t make any sense since the stone that was sealed was the only one having the problem. Since the pool deck stone was set in sand I decided to pull one up. 

I took one stone up and removed a handful of sand. Just as I was about to place some in a baggie to have tested, I thought about the guy during lunch who kept asking me to pass the salt. So, I took some of the sand on my finger and tasted it. BINGO, it tasted like salt. I wondered out loud, “Were the stone setters dumb enough to actually use beach sand?”

I took off my shoes and walked to the beach with a sample of the sand. Just I was about to step on the beach I noticed an area that had a large, dug-out hole. It certainly looked as if someone had been digging up a lot of sand. (Gee, I wonder who?)

 I took a handful of sand from the beach and compared it to the sand in my hand, and bingo – it had the same color and composition. The salt in the sand was wicking into the pavers from underneath! Because it was sealed, it was harder for the salts to escape, so the salts crystallized within the pores of the stone, causing the spalling. 

Now I was going to have to deliver some bad news to the designer, and hope the owners were not really going to take out a contract on her. Another case solved. I wondered if I had time for a swim before she called me.

The Stone Detective is a fictional character created by Dr. Frederick M. Hueston, PhD, written to be entertaining and educational. 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. Send your comments to Dr. Fred at fhueston@stoneforensics.com .