QUESTION
We recently completed a large commercial tile installation, and during the punch list, the owner and architect noted that some tiles sound hollow when tapped. They are now questioning the quality of the installation. Does a hollow sound indicate a failure, and how should this be evaluated?
ANSWER
Thank you for reaching out to the National Tile Contractors Association regarding your concerns.
A hollow sound in a tile installation is a topic that comes up frequently. From an industry standards standpoint, it is important to clarify that a hollow sound, by itself, is not considered a failure or a defect. Sound is not a recognized method for evaluating the performance of a tile installation.
Current industry standards provide more specific guidance on how installations are evaluated. Standards published by the Tile Council of North America and ANSI A108 focus on mortar coverage and support, not acoustics. These standards require:
- Minimum 80% mortar coverage in dry interior applications
- Minimum 95% mortar coverage in wet or exterior applications
- Full support at edges and corners of the tile
- ANSI A108.5.2.2.3 states: “Thoroughly embed all tile or tile assemblies into place to obtain maximum contact of mortar on the back of each tile, or back of each tile and back mounting material. Contact area shall not be less than 80%, or as specified in the contract documents, whichever is greater. Contact area on all exterior installations or interior wet installations shall not be less than 95%. The 80% or 95% coverage shall be sufficiently distributed to give full support of the tile with particular attention to all corners and edges of the tile. To achieve the 80% or 95% coverage, select a notched trowel sized to facilitate the proper coverage. It may be necessary to flat back trowel individual tiles or tile assemblies with bond coat to achieve the proper coverage. Embed the tile or tile assembly in the mortar by pushing in a direction perpendicular to the combed ridges to fully collapse them and achieve the specified coverage. Maintain joint alignment and spacing. Keep an adequate joint depth open for grouting.”
A hollow sound can occur for a variety of reasons, including minor voids, substrate conditions, or, in some cases, the use of membranes within the assembly. In many situations, tile that sounds hollow may still be adequately bonded and performing as intended.
When concerns arise, the only reliable way to evaluate an installation against industry standards is through direct verification of mortar coverage, which typically requires selective removal of tile.
As an association, NTCA is not a consulting or forensic inspection firm and does not perform site inspections, determine compliance on specific projects, or provide legal opinions. If you would like to further investigate your installation, we recommend engaging a qualified, independent tile consultant who can evaluate the installation in accordance with recognized industry standards.
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