What does Hollow Sounding Tiles mean?

QUESTION

What does Hollow Sounding Tiles mean? I just read your article on “hollow” sounding tiles. I just had about 1700 sq ft of 24” x 24” porcelain tiles installed over a post-tension slab foundation. The tiles were installed in a diagonal pattern. The house is 12 years old

The problem: When I step or tap on some of the tiles with a letter soled shoe, I get a high pitched sound on some of the tiles (perhaps 10% of them) which also gives a “hollow” sound to it (some areas of a tile will be more impacted than others). I also get this sound when I drop part of a vacuum cleaner cord on the tile or sometimes when my 8 lb. dauchsund walks on the tile. What confuses me is that your article said that the sound that I should be hearing (if there is a problem) is one of a much lower pitch, rather than a high pitch sound.

The installation: I watched some of the installation and noticed that the tile setter was doing the “spot” placing of thinset but appeared to cover about 55-65% of the tile in doing so. There were some areas where “mud” had to be laid as the concrete foundation was a a little uneven. The floor is now just a little off-level in only one part of the kitchen area and there are no hollow sounds coming from any of those tiles.

THE QUESTIONS: Before I get into a conversation on inadequate installation with my tile contractor, I want to make sure I understand what I am talking about. Because I’ve never heard the sound that I am hearing on any tiles in other installations other than mine, this difference is logically telling me that something is wrong. So, without pulling any of the tiles up, what explanation might there be for experiencing such a sound?

If I do need to pull up a couple of tiles (or more), what should the bottom of the tiles look like that would indicate an installation deficiency?

The other factor I would like to point out is … there are more tiles that are beginning to give (on an ongoing basis) that high pitched sound that also sounds “hollow” to me.

Thanks for any insight that you can provide.

ANSWER

ANSWER - Sound is all relative to the materials and configurations of the tile assembly and whose ears are listening.

A hollow sound can be a higher pitch or a lower pitch depending on the materials and the assembly.   The sound can mean something is not bonded or there is a void, or it may be characteristic of that particular tile assembly.   Generally speaking when only some of the tiles have a different sound it might mean the tile has a void under it or that something is not bonded or you may be hearing a condition within in the substrate itself.   It doesn’t necessarily mean you have a problem.

Sounding is a qualitative test and is subjective.   Normally the sounding test is used when there is resultant damages and it helps the investigator to determine where to look for evidence of the problem so you know can determine the cause of a problem and then how to remediate it.  There are generally compounding deficiencies when there is a problem, so there isn’t a simple answer to say what to look for.  It requires being an expert of the industry standards and having a lot of experience and knowledge about tile assemblies.

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