What is the effect of HPMC on mortar performance?

HPMC (hydroxypropyl methylcellulose) is a widely used additive that can significantly improve the performance of mortar. Here are its main effects:

1. Improve water retention: HPMC improves water retention, allowing free water to stay longer in the mortar. This prolongs the hydration time, improving strength and durability.

2. Enhance workability: HPMC improves the workability of mortar, making it easier to apply. It enhances adhesion, reduces segregation, prolongs open time and minimizes slippage, thereby optimizing construction quality.

3. Improve bond strength: HPMC can significantly improve bond strength. For example, adding 0.2% HPMC can increase bond strength from 0.72 MPa to 1.16 MPa.

4. Effect on flexural and compressive strength: Although HPMC slightly reduces flexural and compressive strength, this effect is controllable within the recommended dosage range.

5. Anti-cracking: HPMC can effectively reduce plastic cracks. At dosages of 0.1% and 0.2%, the cracking index dropped to 63% and 50%, respectively. Beyond 0.2%, further reduction is unlikely.

6. Anti-sagging performance: HPMC can improve anti-sagging performance, prevent mortar from sagging during thick layer construction, and improve construction efficiency.

7. Air entrainment: HPMC can introduce uniform, fine bubbles, improve workability and reduce the risk of cracking.

In summary, HPMC improves mortar performance by improving water retention, workability, bond strength and crack resistance, while controlling sagging. However, the dosage should be optimized to balance the benefits and potential strength reduction. Selecting the right HPMC viscosity and dosage for specific mortar and construction needs ensures optimal performance.