When mortar exhibits poor build-up thickness, sagging during wall application, difficulty in combing, or tile slippage during installation, these are all signs of poor anti-sag/anti-slump performance. The standard JC/T 547-2017 “Ceramic Tile Adhesives” provides a detailed method for measuring sag resistance.

Test Method:

  1. Place the edge of a steel ruler flush with the top of the concrete slab. When the slab is positioned vertically, the bottom edge of the ruler should remain level. Apply a 25mm-wide masking tape directly below the ruler. Spread a thin layer of adhesive over the concrete slab using a straight-edge trowel.
  2. Apply a thicker layer of adhesive over the initial coat, just covering the bottom edge of the masking tape. Comb the adhesive using a 6mm × 6mm (12mm center-to-center) notched trowel.
  3. Hold the trowel at a 60° angle to the slab and draw it parallel to the edge.
  4. Immediately remove the masking tape and place a 25mm-wide spacer (or shim) flush against the bottom edge of the ruler. After 2 minutes, place a ceramic tile (requirements: water absorption by boiling method 0.1%–0.5%, unglazed, surface dimensions 100±1mm × 100±1mm, mass 200±10g, thickness 8mm–10mm) firmly against the spacer. Place a 5.00±0.015kg weight on the tile for 30±5 seconds.
  5. Remove the spacer and measure the distance between the ruler’s edge and the tile using a caliper, accurate to ±0.1mm. Immediately after measuring, carefully position the concrete slab vertically. Remeasure the distance after 20±2 minutes. The difference between the two readings is the maximum sag distance of the tile under its own weight.
  6. Test each adhesive with three tiles. The result reported shall be the average of the tests.

Recommended Solutions:

  1. When sagging occurs in mortar, starch ether is often used. It enhances thickening, improves structural stability, sag resistance, and workability. Alternatively, a thixotropic lubricant may be used to help control viscosity, yield point, stability, and application properties. However, considering overall cost and the potential negative impact of excessive starch ether on adhesive strength, we recommend using a combination of these two additives.
  2. When the dosage of starch ether or thixotropic lubricant has reached its limit with limited improvement in sag resistance, it is advisable to use a functional cellulose ether such as Tempo 30011C. This product can maintain the water retention of tile adhesive while partially replacing starch ether or thixotropic lubricant, thereby reducing overall costs.
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