Should a Marble Floor that was Spot Bonded and Sounds Hollow be Replaced or Restored?


We have an established, very loyal client who wants us to polish their marble foyer, but the whole thing sounds hollow. The homeowner told us that the installers used 4 blobs of mud to attach each tile. It also appears to have been (badly) crystallized at some point. It looks like it would need honing down to maybe a 100. so polishing pads don't seem to be an option. What do you think? Should we go for it, or tell them it all needs replacing? We don't want to further damage their tile with all that moisture.


ANSWER - First of all a hollow sounding marble floor is not considered a defect in itself.   It could be a symptom of a defect.  The only way to determine that is to see what is causing the hollow sound.  It might not have anything to do with the marble tile assembly.

Another consideration is whether there is any resultant damages caused by the condition that causes the hollow sound.  There are cases where a bonded mortar bed is not bonded to its substrate that causes a hollow sound, but the tile assembly is structurally sound.

Spot bonding marble slab or marble tiles is not an approved method of installation.  The excess voids diminish potential bond strength, it leaves voids that could collect moisture in some situations that could cause moisture issues, and the stone is unsupported at the voids.

If there are no resultant damages from the spot bonding, then I wouldn't automatically condemn the floor.  If the marble is 2 cm (3/4") thick or  thicker it might perform ok in a residential application in a spot bonded method.  On the other hand it could be more susceptible to live load damage if it is subjected to heavy loads or impacts.  Also when the floor is restored and subjected to a lot of water, the water could migrate through the grout joints into those voids under the floor and cause efflorescence staining or even spalling in a worst case scenario.

If the marble floor has no resultant damages from the spot bonded hollow sounding floor, you could restore it.  If you do restore it, I would have the client write a disclaimer that you won't be responsible for any resultant damages as a result of the stone being spot bonded.

2 thoughts on “Should a Marble Floor that was Spot Bonded and Sounds Hollow be Replaced or Restored?

  1. Michele Mathews says:

    Our builder installed a very expensive decorative marble medallion in our new home. It has a hollow sound underneath and appears to be bowed up a bit. We are afraid over time it might crack. What should we do and who is responsible for damages should there be any? The builder for faulty installation or the company who made the medallion? How do we fix this situation? Thank you so much!

    • Donato Pompo says:

      Because it is hollow sounding doesn’t necessarily mean there is a deficiency. Depending on the underlying conditions it could be an indication it was installed over a membrane or some other condition. Although the hollow sound could be an indication that there is a deficiency.

      If the medallion is bowed up it depends on whether that is a characteristic of the material or if it was installed that way by the installer or if the material for one reason or another expanded and if there is evidence that it is a defective installation and if it will cause resultant damages.

      The only way to determine if it is a problem and who may have caused the problem, and then determine how to remediate the problem is to perform a forensic intrusive inspection by removing a portion of the medallion. Having a company of our caliber perform the work may or may not be practical.

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