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Why do walls always crack? 90% of the problems are due to the anti-cracking mortar.

1. What Is Anti-Crack Mortar?

Anti-crack mortar is a special modified cement-based mortar designed to prevent surface cracking in buildings. It is produced by adding polymer modifiers, fibers, and other crack-resistant components to cement mortar. It is widely used in external thermal insulation systems, plastering layers, and local structural repairs.

Key Features and Performance

Anti-crack mortar works effectively due to the following properties:

  • High flexibility (low shrinkage): absorbs stresses caused by temperature changes and minor structural movement

  • Excellent adhesion: bonds firmly to concrete, insulation boards, and cement substrates

  • Good tensile strength: according to JG/T 158-2013, the 28-day tensile bond strength should be ≥ 0.7 MPa

  • Durability and environmental friendliness: water-based systems with good freeze–thaw resistance and weather durability

Common Types

  • Polymer-modified anti-crack mortar: the most widely used type, available in standard and high-flexibility grades

  • Dry-mix anti-crack mortar: factory-prepared powder, mixed with water on site for consistent quality

Special products also include high-strength repair mortars and restoration mortars for historical buildings.

2. Application Steps and Technical Requirements

The recommended application temperature is 5°C–35°C. Avoid construction in rain, strong wind, or direct sunlight.

1. Substrate Preparation

  • Substrate must be solid, clean, and even

  • Free from oil, dust, release agents, and loose materials

  • Insulation boards should be flat with tightly filled joints

A suitable bonding primer or interface treatment is usually recommended.

2. Mixing

  • Mix dry mortar with clean water strictly according to the product datasheet

  • Use mechanical mixing for a homogeneous paste

  • Let the mixture rest for a few minutes, then remix lightly before use

⚠️ Do not add extra water or reuse hardened material.

3. Application and Mesh Embedding

  • Apply the first layer with a thickness of 2–3 mm

  • Embed alkali-resistant fiberglass mesh immediately into the fresh mortar

  • Press from the center outward to ensure full coverage

  • Overlap mesh joints by at least 100 mm

Apply reinforcement mesh at corners, window and door openings.

After initial setting (about 24 hours), apply the second layer to fully cover the mesh. The total thickness should be 3–5 mm.

4. Curing

  • Allow natural curing

  • In hot or dry conditions, lightly mist with water

  • Protect from early freezing, rain, and strong sunlight

3. Key Points to Remember

  • Use certified materials compatible with the insulation or plastering system

  • Fiberglass mesh is essential and must be fully embedded

  • Control thickness carefully to avoid shrinkage cracking

  • Ensure continuous application to avoid cold joints

  • Pay special attention to edges and openings


4. Conclusion

Anti-crack mortar performance depends not only on material quality but also on correct application. Proper material selection, accurate mixing, correct mesh embedding, and strict thickness control are the foundation of long-term crack resistance.

For residential projects, experienced workers are recommended. For commercial projects, technical training and on-site supervision are essential.


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