Frederick M. Hueston, PhD

The weather is finally changing down here in Florida. It was brisk a 55 degrees this morning. Of course, you snow birds consider that shorts and flip-flops weather, but us native Floridians break out the parkas, ski masks and gloves. If you have never experienced the cold in the South, it’s way different than the cold in the North. I’ve been told the humidity makes it feel like you’re chilled to the bones.

Anyway, it was a cold enough morning to head over to Flo’s for a warm cup of coffee, and perhaps some bacon and eggs. I grabbed my fedora and trench coat and headed out the door. I hadn’t gotten two steps out of the door, when my phone rang. “Stone Detective,” I said, shivering. The call was from a contractor who had gotten a call back on a granite floor he installed a few weeks ago. It was in a retail store that was about to open. He told me that there appeared to be a light-colored halo around the perimeter of the stone in certain areas. 

He also told me that the phenomenon comes and goes, and seems to be worse when the floor is mopped. I asked him the standard questions, like:

What type of granite was it?

What type of grout was used?

Did they seal the stone?

All his answers were well within the industry guidelines. It was a domestic gray granite. They used a standard cement-based grout, and they had not sealed the stone. 

I have seen this problem on numerous occasions when an epoxy grout is used, so I asked him if he was sure it was not epoxy. He told me the brand name, and sure enough, it was not epoxy. I told him I would have to come out and see it. 

Unfortunately, it was in another state. I could book a flight and be there in less than a hour’s flight time, but this old man is kind of skeptical about the safety of traipsing through airports, and maybe catching the corona bug. Thinking about that, I put the address into my GPS and it would take me about 12 hours to get there. That meant I would need to charge for two days travel. 

I gave him the bad news, and he wasn’t happy. He was huffing and puffing on the phone about my fees, and then I just asked him,  “Do you FaceTime, Skype or even just internet access on your phone at the job site?” He said he did. I told him I could do a virtual inspection. He would need to show me the problem and I would tell him what to do as far as testing, etc. He agreed and we set a time later that day for the inspection. Now maybe I can get that cup of joe and some breakfast.

Later that day, as I sat in my office dreaming of warmer days, my phone alerted me that I had a video call. The tile contractor was on the job site, and had the phone’s camera pointing at his shoe. I told him he had some nice shoes, but I was not a shoemaker and needed to see the problem. He laughed, which kind of helped to break the ice. 

I asked him to show me the areas where this halo was appearing. He walked over to a spot on the floor and said: “That is odd. It was here this morning, and now it’s gone!” I asked him to spill some water on those areas. He grabbed a cup of water and spilled it on the stone, and you could see the stone get darker except for about an inch around the perimeter of the stone. I noticed that the grout joints in that area were shiny, which is uncharacteristic of standard grout. 

Next, I asked him to take a knife and poke the grout. When he did, I could tell it was soft. I told him that was not standard grout. He said, “Yes, I know this is where the expansion joint is, and we used silicone in those areas.”

I asked him if the halo effect was occurring only on the expansion joint areas.

He replied, ”Well now that I think about it, yes!”

Bingo, I thought. I told him this was a classic case of silicone bleeding. The oils in the silicone had bled into the stone. The bleed is invisible when the stone is dry, but when you wet the stone, the silicone waterproofs where it has bled,  causing the stone in that area to stay dry. I told him if it’s a big concern, he could remove the silicone, poultice the area with a silicone digester, and reinstall a soft joint that will not stain.

Finally, I advised him to make sure to test the type of silicone on a sample piece so it doesn’t happen again.  Many silicone manufacturers will test it for you, but you will have to send them a sample of the stone.

Well, that’s another case solved. It was interesting to solve this long-distance, and hardest part was not rolling my eyes, keeping my professional face, and not pulling his leg. For instance, I wanted to tell him that the stone was an angel, since it had a halo. But he was probably thinking it was more like the devil, since he hasn’t received final payment on that job, yet.


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 Gazette for over 20 years. 


Send your comments to fhueston@stoneforensics.com.