Ⅰ.Cause Analysis

1.Loss of Material Reactivity

Once the pot life is exceeded, the cement within the adhesive begins to set and form lumps. Although the surface might still appear workable, the material loses its intrinsic adhesive properties internally. Using it for tiling will likely result in hollow spots (voids) and eventual tile detachment.

2.Significant Reduction in Bond Strength

The bond strength of tile adhesive comes from the hydration of cement and the film-forming "gripping force" of polymers. Within the open time, these polymers are evenly distributed, forming a cohesive network. After this period, the polymers begin to coagulate and can no longer effectively envelop the cement particles. This leads to a drastic drop in bond strength (potentially over 50%). Using it is akin to trying to bond something with partially dried glue—the bond fails easily.

3.Deterioration of Workability and Performance

The material becomes stiff and difficult to spread with a trowel. Forcing its application results in an uneven bed, with areas that are too thin. It also becomes prone to cracking. Some workers add more water to re-liquefy it, but this disrupts the critical water-to-powder ratio. Even if it appears easier to use, the cured adhesive will have a weak, crumbly internal structure—much like a biscuit that has been softened in water and then re-dried, it becomes fragile and loses all strength.

Ⅱ.Solutions & Correct Practices

1.Mix Small, Frequent Batches

Prepare only the amount of adhesive that can be used within its open time, based on your working speed. Mix a new batch only after the previous one is consumed.

2.Monitor Material State

Check the condition by lifting some adhesive with a trowel. If it breaks apart and drops in clumps (with a crumbly, curd-like consistency), it has expired and must be discarded.

3.Manage Environmental Conditions

In hot weather, schedule work for cooler morning/evening hours. In cold conditions, avoid application when temperatures are below 5°C, as low temperatures significantly extend setting times and affect cure.