Large-Format Tile Hollow Sounds — Santa Monica HOA Common Area Failure
Improper Thinset Coverage Documented — Installation Contractor Liable
Acoustic sounding map of lobby floor — red zones indicate hollow
A luxury Santa Monica high-rise HOA discovered widespread hollow sounds across 1,800 sq ft of recently installed 24"×48" large-format porcelain tile in its lobby. The installation contractor claimed the sound was normal and structural — our inspection determined otherwise.
Acoustic sounding survey revealed 62% of tiles were fully or partially hollow
TCNA Handbook requires minimum 80% mortar coverage for floor tile, 95% for wet areas
Tile size (24"×48") requires back-buttering and large-format trowel per TCNA Method F113
Deflection measurements showed floor movement exceeding L/360 tolerance at hollow zones
All 94 large-format tiles sounded with calibrated sounding rod. Results mapped to floor plan with hollow percentage per tile documented.
Grout joint width, depth, and continuity measured at 50 locations. Compared against specification and ANSI A108.5.
Three tiles removed with HOA permission. Thinset coverage percentage measured and photographed before mortar disturbed.
Floor deflection measured under load per IBC Table 1604.3 at hollow vs. solid tile locations.
Removed tiles revealed classic 'spot bonding' — thinset applied in 5 spots per tile rather than full coverage. Average thinset coverage measured at 31% — critically below the 80% TCNA minimum. Back-buttering was not performed despite tile size requiring it per F113.
| Measurement | Result | Standard / Threshold | Status |
|---|---|---|---|
| Thinset Coverage (avg) | 31% | ≥ 80% (TCNA F113) | |
| Hollow Tile Count | 62% of field | 0% acceptable | |
| Back-Buttering Applied | None | Required for ≥15" tile | |
| Max Deflection | L/280 at hollow zones | L/360 max (IBC) |
Forensic Report Outcome
Installation Defect — Inadequate Thinset Coverage and Missing Back-Buttering
The 22-page report with annotated photographs of removed tiles, acoustic sounding maps, and TCNA/ANSI citations was presented to the HOA board and contractor. The report formed the basis of the HOA's demand letter and subsequent legal filing.
Contractor agreed to full re-tile at no cost to HOA — valued at $54,000.