Bathroom Floor Ponding and Hollow Tiles Before Hotel Reopening
A five-star hotel is reopening a guest bathroom in three days. The floor is 5.2 m² and receives 600 × 600 × 9 mm porcelain tiles over an existing concrete slab. The drawing calls for a 1.5% fall to a linear drain at the far end. The tiler sets out from the doorway with 3 mm joints and uses a 10 mm notched trowel without back-buttering. Forty-eight hours later, tiles within 400 mm of the drain sound hollow when tapped, a 2 mm lippage step appears at one tile corner, and a 24-hour ponding test leaves water standing 40 mm from the drain. The hotel has only 12 spare tiles and the doorway cannot be raised more than 15 mm. The manager wants the floor usable for the reopening and asks you to inspect before any replacement begins.
1. From the evidence, diagnose the most probable causes of the hollow sound, lippage, and ponding. Explain how each observation supports or rules out a cause.
Read the worked answer
The pattern points to three linked failures rather than one.
- Hollow sound near the drain: the tiler used a 10 mm notched trowel without back-buttering on 600 × 600 porcelain. Ridges may not have been collapsed, and the mortar likely skinned over before the tile was placed. Air pockets and poor transfer give the hollow note. A hollow tile near a drain is also exposed to repeated wetting, so it is a bond-failure risk, not just a sound.
- Lippage: a 2 mm step at one corner suggests a high spot in the slab or uneven bedding. Because the tiler set out from the doorway, he may have levelled each tile to the doorway rather than to the drain, building up mortar locally. Check the slab with a 2 m straightedge before blaming the tile.
- Ponding: water standing 40 mm from the drain means the 1.5% fall was not achieved. Setting out from the doorway with a level bed tends to flatten the intended slope. The drain may also be set high.
Confirm by lifting one affected tile: check back coverage (target at least 80–90% for wet areas), mortar contact, and straightedge fall. If the substrate is high, rectifying only the surface tiles will fail again.
2. Propose a rectification plan that fits the 3-day reopening, 12 spare tiles, and 15 mm doorway limit. Include sequence and acceptance checks.
Read the worked answer
Work from the drain outward, not from the door.
- Protect the doorway and remove only tiles that fail tap-testing or show lippage, using a grinder with a dust shroud. With 12 spares, do not remove sound tiles unnecessarily.
- Grind high spots; check with a 2 m straightedge (generally no more than 3 mm in 2 m for large-format). If the slab needs correction, use a thin self-levelling compound within the 15 mm doorway allowance; do not simply add mortar, which will raise the floor and shrink.
- Re-establish the 1.5% fall with screed rails or a mortar bed keyed to the drain. Set the drain so its grate sits 1–2 mm below the surrounding tile.
- Fix with a C2TE S1 adhesive, 10 mm notched trowel plus back-buttering, combing in one direction and collapsing ridges. Check coverage by lifting a sample tile.
- Grout after cure, then pond-test for 24 hours; no standing water beyond 2 mm at the drain.
If the 12 tiles are insufficient, tell the manager immediately and order matching dye-lot tiles; do not hide the shortage.
3. Write the message you would give the hotel manager and the record you would keep.
Read the worked answer
Tell the manager in plain terms: the affected tiles failed because the mortar did not bond and the fall was not formed; the repair will take a stated number of hours, and the bathroom will be usable after grout cure. Avoid blaming individuals in the guest-facing message. Record: date and time, area, tile batch, adhesive batch, trowel, coverage observed, straightedge readings, photos before and after, pond-test result, and who signed off. Keep a sample of the failed adhesive if there is a product dispute. State the residual risk: if the slab is uneven beyond the repaired zone, other tiles may debond, so recommend a tap-test of the whole floor. Give the manager a written handover with cure times and cleaning instructions.