Practical Analysis of Energy-Saving Thermal Insulation Materials for Exterior Walls

With the continuous development of the economy and the improvement of living standards, China’s energy consumption has been steadily increasing. Consequently, governments at all levels in China have attached great importance to energy efficiency in buildings and have implemented mandatory promotion policies. After several years of concerted efforts in promoting and applying these measures, initial results have begun to emerge. Enhancing the thermal insulation and energy-saving performance of buildings, as well as improving the technical quality of thermal insulation and energy-saving construction projects, remain the primary focus of research and application in this field. This document provides a comparative analysis for reference by professionals in related industries, including manufacturers of thermal insulation and energy-saving building materials, designers and contractors of energy-efficient building projects, and quality inspection authorities—such as architectural designers, production technicians, construction workers, project supervisors, and quality inspectors.

I. Expanded Polystyrene Board Thin-Coat Render External Thermal Insulation System for Exterior Walls

The expanded polystyrene board thin-coat plaster exterior thermal insulation system was first piloted and promoted in Beijing and then rapidly expanded to Tianjin, Hebei Province, the three northeastern provinces, and even to several southern provinces such as Shanghai, Jiangsu, and Hunan. To this day, it continues to be extensively used in exterior wall external thermal insulation projects, particularly in the cold regions of northern China, making it one of the fastest-growing product systems for thermal insulation and energy conservation in China. The primary insulation material employed is expanded polystyrene foam board, with auxiliary materials including specialized expansion mushroom anchors, alkali-resistant fiberglass mesh, polymer-bonded mortar, finishing plaster, exterior wall coatings, or decorative facing tiles. The construction method involves applying polymer-bonded mortar to adhere the expanded polystyrene foam board to the wall surface, securing it with dedicated expansion mushroom anchors, applying alkali-resistant fiberglass mesh using crack-resistant and waterproof mortar, followed by a 3-mm layer of crack-resistant and waterproof finishing plaster, and finally applying an exterior wall coating or installing decorative facing tiles. Its advantages include excellent thermal insulation and energy-saving performance, as well as relatively standardized construction practices.

II. Exterior Wall External Thermal Insulation System with Rubber Powder and Polystyrene Granules

The polystyrene-bead-in-adhesive powder exterior insulation system is, following expanded perlite insulation materials, a major material used for both interior and exterior wall thermal insulation and energy conservation. It is being promoted and applied in both southern and northern regions, with particularly large-scale implementation in provinces such as Jiangsu, Anhui, Jiangxi, Hunan, and Hubei. Its primary insulating component is polystyrene beads, supplemented by polymer adhesive powder, alkali-resistant fiberglass mesh, and expansion mushroom anchors. The construction process involves pre-mixing the polystyrene beads with the polymer adhesive powder and water until a uniform slurry is obtained (the polymer adhesive powder and polystyrene beads are packaged separately and mixed with water just before use). The slurry is then evenly applied to the wall in layers 20 mm thick; after each layer has dried, an alkali-resistant fiberglass mesh is adhered, followed by a 3–5 mm layer of waterproof, crack-resistant mortar. For tile finishes, galvanized wire mesh and expansion mushroom anchors must be used for secure fixation, after which an exterior paint coating or tile cladding is applied. The advantages include excellent thermal insulation and energy-saving performance, easy adhesion between the insulation layer and the substrate with relatively low requirements for substrate flatness, simple construction procedures, lower project costs, and a reduced likelihood of widespread cracking, hollowing, or detachment. Technically, the system is also viable: because the mixed slurry is as easy to handle as traditional cement-based skim coats and exhibits very good bond strength, it is readily amenable to widespread adoption. The main technical trade-off in the polystyrene-bead-in-adhesive powder insulation system concerns the relationship between insulation performance and structural strength: the higher the polystyrene bead content in the insulation slurry, the lower the cement-based adhesive powder content, resulting in lower structural strength but better thermal insulation; conversely, the higher the cement-based adhesive powder content, the lower the polystyrene bead content, leading to greater structural strength but poorer thermal insulation.

III. Inorganic Thermal Insulation Mortar (or Vitrified Microsphere Thermal Insulation Mortar) System

The inorganic thermal insulation mortar system (or vitrified microsphere thermal insulation mortar system) is a new type of thermal insulation material. It uses inorganic hollow vitrified microspheres as the insulation core, combined with a polymer-based adhesive slurry, resulting in an insulation layer composed of tens of thousands to hundreds of millions of tiny hollow insulating vitrified microspheres per square meter. The advantages of this highly dense, integrated microsphere-based insulation system include: 1) the vitrified microspheres are inorganic, providing excellent fire resistance; 2) high compressive strength and high shear-adhesion strength; 3) good weather resistance, low drying shrinkage, and no need for mesh reinforcement; and 4) simple construction and lower project costs. However, there are also some drawbacks: due to the relatively high density of the inorganic vitrified microspheres, the finished dry density typically ranges from 420 to 450 kg/m³, which leads to a higher thermal conductivity—generally above 0.096 W/(m·K)—and consequently poorer thermal insulation and energy-saving performance. To achieve thermal insulation and energy-saving performance comparable to that of polystyrene bead-in-polymer powder systems, it is common practice to increase the insulation thickness. Yet, because of the higher density of the vitrified microspheres, increasing the insulation thickness also increases the self-weight of the system, which inevitably compromises the long-term stability and safety of the insulation system. Therefore, when energy-saving targets reach 50% to 65%, this insulation system is not suitable and fails to meet the required energy-saving standards.

The key to the construction of wall substrates, thermal insulation and energy-saving layers, and exterior wall finishes lies in the selection of materials and construction techniques. As architecture is a long-term undertaking spanning centuries, the level of building technology and decorative craftsmanship reflects a nation’s and a people’s cultural and scientific-technological sophistication, and bears directly on the well-being of future generations; therefore, it cannot be judged solely on short-term considerations. The technical soundness and quality of the thermal insulation layer not only have a direct impact on the efficiency of heat preservation and energy savings, but also pose significant quality and safety risks for subsequent exterior wall finishing works. Energy conservation and reduced energy consumption are a long-term national policy and a crucial step toward achieving sustainable development of the national economy.