Key Technical Points for the Application of HPMC in Spray Plastering

Spray plastering, as a mechanized interior wall construction technique, offers advantages such as high efficiency, excellent smoothness, and low labor costs. Hydroxypropyl methylcellulose (HPMC), a key functional additive, significantly improves the slurry's workability, water retention, and bond strength.

I. Mechanism of Action of HPMC

HPMC is a non-ionic cellulose ether that optimizes the performance of spray plastering through the following mechanisms:

Water Retention and Thickening: Forming a hydrated network structure inhibits water loss, ensuring full hydration and crystallization of the gypsum, and enhancing final strength.

Improving Workability: Regulating the slurry's viscosity and rheological properties to ensure smooth pumping and uniform spraying, reducing the risk of pump blockage and splashing.

Enhancing Adhesion: Improving the slurry's wettability, strengthening the bond with the base layer (brick-concrete/concrete/lightweight masonry), and reducing hollowing and cracking.

Preventing Sagging and Segregation: Maintaining the slurry's structural stability, preventing sag during construction on vertical surfaces, and preventing aggregate settling and stratification.

II. HPMC Selection and Dosage

Dosage Range: The recommended addition amount is 0.1%–0.3% of the gypsum mass, subject to dynamic adjustment based on formulation design, ambient temperature and humidity, and application requirements.

Key Selection Factors:

Viscosity Grade: Prefer medium-to-high viscosity grades (typically 40,000–75,000 mPa·s) to balance water retention and application fluidity.

Substrate Compatibility: Optimize the degree of substitution of methoxyl (DS) and hydroxypropoxyl (MS) to ensure thickening efficiency and hydration stability.

Solubility: Select a fast-dispersing product to reduce on-site mixing time and improve application efficiency.

III. HPMC Performance Advantages

Application Efficiency: Extends working time, ensuring continuous pumping and spraying stability.

Finished Product Quality: Forms a dense, smooth gypsum layer, eliminates hollowing and cracking, and provides a high-quality base for the finishing layer.

Substrate Compatibility: Excellent adhesion to various substrates and excellent environmental adaptability.

Overall Benefits: Effectively lower overall construction costs by reducing rework and material loss.

IV. Application Specifications and Precautions

Quality Control: Select HPMC products with stable viscosity and degree of substitution that meet standards to ensure slurry water retention and pumping stability.

Dynamic Adjustment: Optimize the HPMC dosage and type based on seasonal temperature and humidity fluctuations.

Material Compatibility: Verify the synergistic effect of HPMC with other additives in the formulation (such as retarders and air-entraining agents).

Pumping System Compatibility: High-viscosity models must match the equipment's delivery pressure to avoid system overload.