Large-Format Porcelain on a Curved Feature Wall
A hotel lobby has a curved feature wall, radius 1.2 m, 3.6 m high, to be clad in 1200 x 600 mm, 9 mm thick rectified porcelain tiles in a stacked bond. The wall is rendered masonry that is sound but has a 6 mm bow over its height. The designer wants tight 2 mm joints and no visible lippage. The adhesive specified is a standard cement-based tile adhesive. Site temperature is 34 degrees C and the wall is in direct sun for part of the day. The tiler on the previous shift set the bottom two rows with a 6 mm notched trowel and butt joints, and several tiles have already debonded.
1. Diagnose why the first rows failed and list the changes needed before continuing.
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Several compounding faults:
- Wrong adhesive. Standard cement adhesive is not suitable for 9 mm large-format porcelain, which is nearly impervious. It needs a deformable, high-bond adhesive designed for large-format/low-absorption tiles, and the substrate and tile back should be primed as specified.
- Insufficient coverage. A 6 mm notch on a bowed wall with large tiles will not achieve the required high coverage (typically 90%+ in wet or external areas, and full bedding for large-format). Voids behind tiles cause point loads and debonding. Use a larger notch (10-12 mm) and back-butter the tiles, combing in one direction.
- Butt joints. Butt joints with no gap leave no room for movement and prevent proper grout fill. The design calls for 2 mm joints - these must be maintained with spacers or a joint system.
- Wall bow. A 6 mm bow over the height means the substrate is not flat enough for tight-joint large-format work. The wall needs to be flattened with a render or patching compound, or the tiles need a thicker adhesive bed managed carefully - but flattening the substrate is the correct fix.
- Heat. At 34 degrees C in direct sun, adhesive skins over quickly. Work in smaller batches, shade the wall, and never re-temper adhesive.
Remove the failed rows, grind back, re-flatten the wall, then restart with the correct adhesive and joint width.
2. How would you set out and fix tiles around the 1.2 m radius while controlling lippage and maintaining the 2 mm joints?
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Curved walls with rigid rectangular tiles require planning because the tile cannot bend.
Setting out. Calculate the chord and the number of tiles per course so joints stay within 2 mm. On a 1.2 m radius, each 600 mm tile spans a significant arc; the gap at the back face will differ from the front. Work out the maximum tile width that keeps the joint at 2 mm at the face - wider tiles on a tight radius will either close the joint at the back or open it at the front. If 600 mm tiles cannot hold 2 mm joints, propose a narrower module or a different bond to the designer; do not force it.
Fixing. Use a deformable large-format adhesive, back-butter each tile, and use a tile levelling clip system to hold adjacent faces flush while the adhesive sets. Check with a straight edge and level across courses, and use a profile gauge or template to confirm the curve. Maintain joints with 2 mm spacers, removing them before grout. Work top-down or in manageable lifts with support, and protect from sun. Allow movement joints at the corners and at maximum intervals per standards.