The Application of Expanded Polystyrene in Building Insulation Materials

The Critical Role of External Wall Insulation Materials

In building envelope structures, the heat loss through the exterior walls is significant, accounting for about 28%. The heat loss ratios of different components are as shown in the figure. It is evident that insulation of the building's exterior walls plays a crucial role in energy conservation. Developing an effective insulation system has become the key to exterior wall insulation. Choosing insulation materials with low thermal conductivity can reduce the overall heat loss of the wall, not only providing excellent thermal insulation but also enhancing indoor comfort, thereby improving the social benefits of the project.

2 Rigid Polyurethane Foam Plastic

Insulation materials for building facades are categorized into two main types: inorganic and organic insulation materials. Inorganic insulation materials boast good fire resistance but lack satisfactory insulation performance and energy-saving effects; examples include rock wool, slag perlite, and foamed cement boards. Organic insulation materials offer good thermal insulation properties but are inferior in fire resistance; they mainly include expanded polystyrene (EPS), phenolic foam (PF), and rigid polyurethane foam (PUR).

Polyurethane foam plastics were developed in the 1950s and quickly gained popularity due to their low production costs. They are categorized into three types: soft foam, semi-rigid foam, and rigid foam. Rigid polyurethane foam products have low thermal conductivity, are lightweight, and offer excellent thermal insulation properties, making them extensively used in building exterior insulation materials. Applying rigid polyurethane foam to building exteriors provides both thermal insulation and waterproofing benefits.

Insulation Performance. Rigid polyurethane foam is a natural adhesive material that, when bonded to wall materials, forms a continuous insulation layer. The insulating effect of 1 cm thick rigid polyurethane foam is equivalent to that of 3 times the thickness of traditional materials.

2. Waterproof Performance. Compared to other thermal insulation materials, rigid polyurethane foam plastic boasts various excellent characteristics such as a low thermal conductivity coefficient, small volume density, and good adhesion properties. The high strength of rigid polyurethane foam plastic allows it to withstand significant pressure in wall structures for exterior insulation, making it less prone to cracking and maintaining insulation for a relatively longer duration. Additionally, rigid polyurethane foam plastic can be installed on-site, with lower construction costs and easier maintenance and repair. The performance features of rigid polyurethane foam plastic include:

(2) Low volume density. Rigid polyurethane foam plastic is lightweight and highly durable, capable of supporting certain loads. Its density is generally between 35 to 40 kg/m³, making it an ideal thermal insulation material for construction.

(3) Excellent bonding performance. Rigid polyurethane is foamed into shape through a spray gun and directly applied to walls. Due to its permeability and fluidity, it firmly adheres to the base layer of the wall. It can form high-intensity bonds with materials such as metal, wood, and glass.

3 Comparison of Rigid Polyurethane Foam Plastic Insulation Technology for Building External Walls

Dry-hanging method

First, install light steel frame skeletons on the building's exterior walls, followed by anchoring rigid polyurethane panels to the outer surface, akin to the dry-hanging technique used for stone. Dry-hanging offers advantages such as direct panel shaping, standardized dimensions, large-scale production capabilities, simple construction operations, and minimal environmental impact.

3. 2 Paste Method

By securing rigid polyurethane panels to the exterior wall with clay, a layer of mesh is then applied. The surface is finished using polymer cement mortar, similar to the construction method of extruded polystyrene panels. The adhesive method offers advantages such as direct board shaping, standardized dimensions, mass production capability, and a smooth粘贴 surface.

3. 3 Field casting method

First, a mold is constructed using a template, followed by the pouring of the mixture. Once the rigid polyurethane mixture has cured, the mold is removed. Then, a layer of mesh is laid down, and a polymer cement mortar is applied, resembling the concrete pouring process. The in-situ casting method offers advantages such as a smooth surface, good integrity, cost savings in materials, and reduced environmental pollution.

3. 4 On-site Spray Painting Method

Rigid polyurethane blends are sprayed onto the exterior walls of buildings through high-pressure spray guns, forming an insulating layer after foaming. The surface is then covered with polymer cement mortar, followed by the application of glass fiber or steel wire mesh. This technology is currently well-established. The rigid polyurethane foam has excellent self-adhesive properties, eliminating the need for a primer, and achieves full adhesion with substrates like metal, wood, and glass. It boasts excellent wind uplift and negative wind pressure resistance. The spray-applied rigid polyurethane foam is applied in a single-coat process, forming a one-time mold, which eliminates the occurrence of "hot spots" and "cold bridges," providing excellent thermal insulation. Additionally, the spray application is quick, with no special treatment required for irregular shapes. A single spray unit can cover 600㎡ per day, and it cures within 5 minutes after spraying, ensuring high construction efficiency.

Case Analysis of the Application of Spray-Rigid Polyurethane Foam Plastic in Insulating Building Facades

4.1 Project Overview

The雅居园ConstructionProject is located in a city in our country and is a energy-saving residential building. It employs spray-applied rigid polyurethane foam plastic as an energy-saving measure for the exterior insulation of all residential buildings. The north and south facades use a 60mm thick rigid polyurethane foam plastic insulation system, while the east and west gables utilize an 80mm thick rigid polyurethane foam plastic insulation system.

4. Preparations

4.2.1 Material Preparation

① Polyurethane. ② Catalysts, defoamers, and foaming agents. ③ Alkali-resistant coated glass fiber mesh. ④ Adhesive. ⑤ Water.

4.2.2 Construction Preparation

Before construction, the certification of the polyurethane must be inspected to meet national material standard regulations. Additionally, the technical specifications of the bonding agent should be verified, and only upon passing the re-examination can it be used.

Before painting, inspect the quality of the wall base, adjust the construction parameters and preheat the materials according to the working environment, and conduct a trial spray.

(3) Add appropriate catalysts, defoamers, and foaming agents to polyurethane to produce rigid polyurethane foam plastic.

4. Construction Techniques

4. 3. 1 Water-Resistant Undercoat Spray

The construction site should be thoroughly cleaned before applying moisture-proof primer after inspection. Pre-installed pipes (components) to avoid installing pipelines and accessories after the moisture-proof primer is applied.

4.3.2 Spray Polyurethane Foam

Spray the rigid foam polyurethane layer starting from the corners, maintaining a thickness of approximately 5mm, with the spray gun positioned 600mm from the wall. Conduct multiple coatings, each with a thickness of around 15mm, until the desired spray thickness is achieved.

4. 3.3 Spray Brushing Interface Agent

After 4 hours of pre-coating, apply the primer using a roller brush to the surface of the insulation layer.

4. 3. 4 Paste cakes and make dots

Bonding and leveling are performed to even out the wall surface, specifically by...

(1) Using a 2-meter ruler and a 2-meter string line to check the wall flatness and the perpendicularity of the board wall surface.

(2) Standard insulation panels (5cm x 5cm) are used as the adhesive tiles, placed approximately 10cm from the top and bottom of the floor, as well as at the positive and negative corners of the large walls, with one tile every 1.5 meters.

After pasting the tiles, check the vertical alignment with a 2-meter plumb line, verify the horizontal consistency with a string line, and record the thickness of the grout.

3.5 Laying alkali-resistant glass fiber mesh

Nатриум-resistant glass fiber mesh is pre-cut to size, with the overlapping direction in the order of left to right and top to bottom, with an overlap width greater than 50mm, and the overlap width at the positive and negative angles greater than 150mm. The application area of the anti-crack mortar is equivalent to that of the alkali-resistant glass fiber mesh, with the mortar being well-packed, controlling the thickness to around 3~5mm. In case of insufficient packing, apply a second coat. After the application is complete, use a steel trowel to press the anti-crack mortar into the mesh.

4. Construction Precautions

During on-site spraying, it is crucial to strictly adhere to environmental weather factors. Construction should be carried out under conditions of temperature ranging from 5 to 40°C, wind speed of ≤3 levels, and relative humidity of ≤70%. Construction is strictly prohibited under conditions of rain, snow, or fog.

(2) The wall base must be flat, dense, free from loose dust, brittle, delaminated, or bulging.

(3) Control the curing time of rigid polyurethane foam to approximately 15 minutes.

During the spraying process, to ensure a firm bond between the insulation layer and the base, constant checks on the foam quality should be conducted.

(5) During the installation of rigid polyurethane plastic, workers must take proper protective measures, strictly prohibit any open flame on-site, and implement measures to prevent the dispersion of foam particles.

(6) After construction is completed, a water-injection test must be conducted to ensure no leakage occurs.

5 Conclusion

As the demand for energy grows, the construction industry in our country is strongly promoting the application of energy-saving and environmentally friendly products. The use of expanded plastic materials has a significant impact on the thermal insulation performance of building facades. Rigid polyurethane foam, as an efficient thermal insulation material, is increasingly attracting attention from the construction industry. Through the aforementioned research, it can be seen that rigid polyurethane foam meets the requirements of construction use and offers good economic and social benefits. The following conclusions can be drawn:

(1) Utilizing on-site mechanized equipment for spray application and shaping, this method boasts ease of operation, high construction efficiency, and low cost. Compared to traditional methods, it reduces raw material consumption and labor costs.

(2) The rigid polyurethane foam plastic is applied through layered spraying, offering strong integrity and the ability to form high-strength bonds with metals, woods, and glass. This contributes to the protective function of thermal insulation and leakage prevention for the building's exterior wall within the entire structural system.

(3) Follow principles such as "合理 design, strict material selection, and optimized construction" for spraying rigid polyurethane foam plastics to ensure the anticipated results.