Frederick M. Hueston, PhD  

Stone Care Consultant 

Peeling limestone balusterIt  was one of those crisp fall mornings. You could smell the leaves as they fell off the trees. The air was brisk, not too cold but just enough for a light jacket – a great morning for a walk.       

I grabbed my jacket and headed out the door. Walking along the sidewalk I noticed a lot of people out walking as well. It’s amazing how many people come out when the weather is changing. 

As I walked and said hello to countless neighbors, my phone suddenly rang, disturbing my peaceful stroll. But I was in a good mood and told myself that nothing was going to upset me today, so I answered the phone in a very upbeat, cheerful way. 

The person on the other end sounded very serious– he kind of reminded me of that political commentator Ben Stein. He proceed to explain that he was a general contractor building a $40 million home, and that they had some new limestone balusters along the back of the house that were peeling. “Peeling?” I said. “I don’t think I have ever seen stone peeling.”

 He continued on and on about how expensive this stone was and was wondering if I could come and take a look. Well, my curiosity got to me so I told him I could be there in a few hours. I had to see this peeling stone for myself.

As I pulled up to this $40 million mansion, parked in front of it was a Bentley, a Mercedes and a Rolls Royce. My ol’ Woody seemed out of place, but at least my ride didn’t cost me a small fortune. As I was getting out, the contractor came walking out the front door. Now, you’re not going to believe this, but he looked just like Ben Stein. As a matter of fact, I thought it might be him. 

He shook my hand and said, “Hi, I’m Fred Stein.” I about fell over in amazement so I had to ask if he was related. He didn’t even crack a smile and said, “Yes, Ben is my brother,” and proceeded to lead me into the house.

As I stepped inside I thought I was walking into a museum. There were marble statues all over the house along with what looked like some Picasso originals hanging on the wall. Got me wondering who owned this monster collection. As we walked through the house toward the backyard, Mr. Stein was talking in that solemn, monotone voice. He was also talking very quietly – barely above a whisper. 

Now, this old man’s hearing is not as good as it used to be so I didn’t catch all he was mumbling. He led me to the balusters, which wrapped around the entire back patio. There where hundreds of them (see the photo)! We went over to one and sure enough – the limestone was peeling. The technical term for this is exfoliation. 

I reached down and peeled a layer off one of the balusters. It was clear that the layers were separating, but the ultimate question was why? So I put on my detective hat and started asking all kinds of questions. 

Mr. Stein proceeded to bore me with all the details from selecting the material all the way through to the way it was installed. I swear I nodded off a few times. He went on and on, and then he told me something that woke me up. He said they “sealed the stone with a good quality impregnator.” Bingo, I thought. I have seen this before and this is an argument I get in with contractors all the time. 

But before I get into that argument, let me explain what was happening. I looked at Mr. Stein and told him the problem is that the stone was sealed when there was still moisture in the stone. The impregnator is blocking the moisture from escaping and it is causing the layers in the limestone to separate. Unfortunately the only solution is to replace the stone and DO NOT seal it.

Now, for my argument. Impregnators are wonderful products and can prevent staining in many different situations. But with that said, there are contractors who think they need to seal everything. The biggest mistake is sealing exterior stone. 

In humid environments this is especially true. The exfoliation I saw in this project is just one in hundreds that I have seen. Now, some will argue that impregnators are breathable. This is true – however, they are only breathable to water vapor, not the liquid state. 

If moisture is inside the stone it cannot escape, in this case, and when it tried to, it caused pressure within the stone, resulting in exfoliation or spalling. So the lesson here is to be careful using impregnators in exterior situations.

The Stone Detective is a fictional character created by Fred Hueston, written to be entertaining and educational. He 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. You can send any email comments to him at