Tile adhesive does not remain ready indefinitely after it is spread. Open time is the period in which the adhesive can receive the tile under the stated conditions. If the surface skins over first, the tile may sit on a layer that no longer bonds as intended.
Conditions change the working window
Heat, airflow, substrate absorption, sunlight and the size of the spread area can all affect how quickly adhesive changes. A Durban renovation may experience very different conditions between a shaded interior wall and a hot, ventilated room with open windows.
The manufacturer’s technical data sheet is the correct reference for the product being used.
A tile can still look fixed
The danger is that a skinned adhesive bed may not look obviously wrong once the tile is pressed into place. A smooth finished face does not prove that the adhesive achieved the intended contact and bond.
That is why installers work in manageable areas, check the bed and adjust their process to the actual room conditions.
Large tile makes the timing more important
Large-format pieces take longer to lift, position and move into place. The handling plan should be ready before the adhesive is spread. A rushed placement or an oversized spread can turn a manageable material into a difficult installation.
The right response is not more adhesive
If adhesive has skinned, it should be dealt with according to the product instructions. Adding more material on top or pressing harder does not automatically restore the original working properties.
Technical installation quality is often about respecting time as much as choosing the right product.
Read why adhesive coverage matters on large-format tile, or see why premium tile needs protection after installation.