Fireplace Hearth - Odd Phenomenon

Conducted a warranty inspection this week and came across an odd issue. Homeowner stated it’s happened only a couple of times in the first 11 months of occupancy. At the base of the hearth front (in line with a couple of mortar joints) a small amount of sand randomly appears on the floor. At first I was thinking sawdust and WDI, but it is clearly sand. My suspicion is slight movement of the finish materials when the homeowner sits or stands on the hearth. Anyone seen something similar? More expert hands care to chime in?

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Yes, a long time ago and it was bugs of some sort (don’t remember) pushing the sand up and out, from below, making themselves a home.

Just a guess here though…


Thanks Larry, I hadn’t thought about bugs other than termites!


Maybe they set the bottom course, filled the void with sand, then set the top stones.

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Hard to tell without other information. I see you’re in Georgetown.

  • Was this a typical manufactured firebox like we see so much here?
  • Is this a slab foundation?
  • Was this on an outer wall?
  • Where are the nearest plumbing fixtures, excluding across from this, whose lines (fresh or waste) penetrate the slab?

Hi Emmanuel,
Thanks for chiming in, the particulars are:
Yes, it’s a typical manufactured firebox, nothing special.
Yes, it’s a slab foundation
No, not an outer wall, the fireplace is located roughly in the center of the first floor of the home.
No plumbing fixtures nearby, (never know where they are routed in the slab of course.) But the kitchen is on the opposite wall from the fireplace and there are no bathrooms near the hearth.
I’m thinking sand base for the hearth as Steven Payson suggests, and just minimal shifting when the client applies weight or pressure to the front of the hearth. In the final analysis I instructed the client to monitor for any changes and contact a masonry contractor if it gets out of hand. All in all not a major concern, more for my own education. One of the joys of home inspecting, we never stop learning, from seeing new things! Thanks again for your input!