Cellulose ethers are commonly used additives in cement mortar to improve its properties and performance. Some of the main roles of cellulose ether in cement mortar include:

1. Water retention: Cellulose ethers can help to retain water in the mortar, which is important for maintaining workability and preventing cracking.

2. Improved workability: Cellulose ethers can improve the workability of the mortar, making it easier to apply and shape.

3. Increased bonding strength: Cellulose ethers can increase the bonding strength between the mortar and the substrate, improving the overall durability of the structure.

4. Reduced shrinkage: Cellulose ethers can help to reduce shrinkage in the mortar, which can minimize cracking and improve the overall appearance of the structure.

5. Enhanced adhesion: Cellulose ethers can enhance the adhesion of the mortar to various surfaces, improving the overall strength and durability of the structure.

6. Improved resistance to water and chemicals: Cellulose ethers can improve the resistance of the mortar to water and chemicals, making it more suitable for use in harsh environments.

7. Increased cohesion: Cellulose ethers can increase the cohesion of the mortar, which helps to prevent segregation and settling of the mix.

Overall, the addition of cellulose ether to cement mortar can significantly improve its properties and performance, making it a more effective building material.