Blog

In external thermal insulation systems, the performance of both adhesive mortar and rendering coat mortar directly affects the durability, crack resistance, and construction efficiency of the entire system. Hydroxyethyl methyl cellulose (HEMC), as a key additive, plays an irreplaceable role.

1. Chemical Characteristics of HEMC and Its Adaptability to Mortar

HEMC is a non-ionic cellulose ether produced by chemical modification of natural cellulose. Compared to ordinary methyl cellulose (MC) or hydroxypropyl methyl cellulose (HPMC) – such as the commonly used HPMC MP 75EX – HEMC offers a lower gel temperature and better salt resistance. These properties make it particularly suitable for electrolyterich external insulation mortars containing cement, gypsum, etc.

In ETICS, mortars are often applied onto highly absorbent substrates such as EPS boards, XPS boards, or concrete walls. The core value of HEMC lies in:

Water retention: Prevents water from being absorbed too quickly by the substrate or lost by evaporation, ensuring sufficient hydration time for cement.

Thickening and thixotropy: Improves workability, prevents sagging, and allows application at a certain thickness.

Extended open time: Gives workers more time to adjust the mortar or place tiles.

2. Specific Applications in the Two Types of Mortars

Adhesive mortar:

Increases initial adhesion and fully wets the surface of insulation boards.

Prevents sagging and maintains the shape of adhesive strips.

Avoids hollowing at the bonding interface.

Rendering coat mortar:

Key to crack resistance – reduces the risk of plastic shrinkage cracking.

Improves lubricity for easy thinlayer application.

Works synergistically with redispersible polymer powder to enhance flexibility.

3. Advantages of HEMC Over Other Cellulose Ethers in ETICS Mortars

In practical engineering, ETICS mortars often prefer HEMC over HPMC or MC. The reasons are as follows:

Lower gel temperature
HEMC has a gel temperature of approximately 60–70°C, while HPMC (e.g., HPMC MP 75EX) typically gels at 50–55°C. During summer construction, darkcolored insulation boards or walls exposed to sunlight can exceed 50°C. If a standard HPMC like MP 75EX is used, the mortar may lose its water retention effect before hardening, leading to dusting or cracking. HEMC maintains stable performance under such conditions.

Better alkali resistance
During cement hydration, a large amount of calcium hydroxide is produced, creating a highly alkaline environment (pH ≈ 12–13). HEMC retains its viscosity better than HPMC in alkaline conditions, thus providing more durable water retention and thickening action.

Excellent mould resistance
External walls are often exposed to humid conditions. Compared to some modified starches or ordinary cellulose ethers, HEMC is less prone to microbial degradation, which extends the shelf life of drymix mortars.

Let me know if you would like to add a short conclusion or a product recommendation paragraph featuring HEMC alongside MP 75EX.