According to the two Chinese standards for tile adhesives—GB/T 25181-2019 (Ready-mixed Mortar) and JC/T 547-2017 (Ceramic Tile Adhesives)—the wet tensile bond strength must be no less than 0.5 MPa (for C2-type adhesives, the requirement is ≥ 1.0 MPa).
Testing Method
1. Cure the specimens under Standard Condition 1 (temperature: 23±2°C, relative humidity: 50±5%, air circulation < 0.2 m/s) for 7 days.
2. Submerge the specimens in standard-temperature water (23±2°C) for 20 days.
3. Remove the specimens, wipe off surface moisture, and bond the pull-head to the tile.
4. Place them back in Standard Condition 1 for 7 hours, then resubmerge in water for 17 hours.
5. Immediately after removal, measure the tensile bond strength at a loading rate of 250±50 N/s.
Recommended Solutions
1.Early-Strength Agents (e.g., Calcium Formate)
Enhance early strength during the initial 7-day curing, reducing strength loss after 20-day water immersion, aiding compliance with standards.
2.Redispersible Polymer Powder (RDP)
RPP (e.g., VAE-based) improves tensile strength, flexibility, and cohesion. However, due to its limited water resistance, standard (C1) tile adhesives may require higher dosages, while C2-grade adhesives should use ternary/acrylic/SBR-based polymers for better water resistance.
3.Metakaolin Additives
Metakaolin’s reactive aluminosilicate reacts with calcium hydroxide (Ca(OH)₂) from cement hydration, forming gel-like C-A-S-H and secondary C-S-H phases. These hydrates enhance compressive/flexural strength, toughness, and accelerate early/long-term strength development.
: How to Improve Wet Tensile Strength?){kind=link}