Large-Format Wall Tiles Sliding in Hot Weather
A tiling crew is fixing 800 × 800 × 10 mm porcelain tiles to a 3.6 m × 2.7 m cement-rendered wall in a shopping mall. The air temperature is 34 °C and the wall is in direct sun. The specified adhesive is a standard cement-based C1 product. A 20 kg bag is mixed with 6.5 L of water although the bag states 5.2 L. After a 10-minute slaking period the mix is re-whipped and used for 45 minutes. Tiles are laid with a 10 mm notched trowel and no back-buttering. Within 20 minutes, tiles slide down 2–3 mm; the next morning, two tiles have fallen and the adhesive ridges are still visible and glossy on the back of a fallen tile.
1. Identify the causes of the slipping and failure, linking each site detail to the observed symptom.
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Several controls failed at once. The mix was 6.5 L instead of 5.2 L, about 25% too much water; that lowers viscosity, increases shrinkage, and makes the adhesive unable to hold an 800 × 800 tile on a vertical wall. At 34 °C in direct sun, the wall and adhesive lose water fast; open time is shortened, so by the time a tile is placed the surface has skinned. Using a batch for 45 minutes exceeds normal pot life and open time. C1 is a standard adhesive; large-format porcelain on a wall needs at least C2, and for this condition C2TE S1 is appropriate (improved adhesion, extended open time, reduced slip, deformable). A 10 mm trowel without back-buttering gives poor coverage on a 10 mm porcelain tile. The glossy ridges on the fallen tile indicate the mortar never wetted the tile back.
2. Specify the correct adhesive and application method for this wall.
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Use C2TE S1, mix exactly to the bag ratio with a clean measuring jug, mix 3–5 minutes, slake 5–10 minutes, and remix briefly. Do not add water after slaking. Shade the wall and work in sections no longer than can be covered within the open time (often 20–30 minutes at 20 °C; much less at 34 °C). Use a 12 mm notched trowel for 800 × 800, back-butter the tile with a thin even coat, and comb adhesive in one direction. Press and slide the tile 2–3 mm to collapse ridges, then use spacers or a slip-resistant system. Check coverage by lifting one tile per 10 m². Discard adhesive that has skinned; never remix it with water.
3. Describe a field check for open time and the corrective action for the fallen tiles.
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Field check open time: comb a small area, touch the ridges with a clean finger every few minutes; when the surface no longer transfers wet mortar to the finger, the open time is over. Also place a tile and lift it; if ridges are not transferred, the adhesive is too dry. Corrective action: remove the two fallen tiles and any tile that sounds hollow; scrape off cured adhesive without damaging the render; check wall flatness; re-fix with the correct adhesive and back-buttering. Do not simply stick the fallen tiles back onto the old ridges. Record the batch numbers and weather. If the wall is in direct sun, fix shade netting and schedule work for cooler hours.