Development of building insulation putty

Wang Xia, Guo Yanyan, Lai Xueping
(Fujian Building Research Institute, Fujian Construction Engineering Technology Development Co., Ltd., Fuzhou, Fujian 350025, China)

Abstract: Building insulation putty is developed, and the preparation process, the amount of vitrified microbeads, and the amount of hydroxypropyl methylcellulose ether and silicone hydrophobic agent are discussed to the strength, water resistance, workability and heat insulation of the putty The impact of performance, the resulting product has a low thermal conductivity, good compressive strength and good water resistance.

0 Introduction
With the advancement of urbanization in China, the proportion of building energy consumption in total social energy consumption is close to 30%, which is 2 to 3 times that of developed countries with the same climatic conditions, and there is a lot of room for energy conservation. In view of this, national and local government departments have issued a series of building energy conservation policies, regulations and standards. The use of building energy-saving materials can improve the building’s thermal insulation effect and reduce the air-conditioning heating energy consumption, which is an effective means for building energy conservation. As an example, the outer wall insulation is mainly implemented by expanded polystyrene board plastering system, extruded polystyrene board plastering system, colloidal powdered polystyrene particle exterior wall thermal insulation mortar, inorganic vitrified microsphere thermal insulation mortar, and the like. As a common exterior wall insulation material, thermal insulation mortar has the disadvantages of single function, poor thermal insulation effect, and easy cracking. Therefore, it is particularly important to study the substitutes for insulation mortar. 

At present, the exterior wall insulation systems of building insulation putty and building reflection insulation coatings have been used in some hot summer and warm winter areas. Reflective thermal insulation coatings have the advantages of thin coatings and good thermal insulation effects, and can be substituted into energy-saving designs as equivalent thermal resistance. In addition to the functions of filling and finding equality, thermal insulation putty has the effects of crack resistance, enhancement and energy saving. It can be used in conjunction with reflective insulation coatings to replace thermal insulation mortar and exterior wall finishing materials, which not only greatly shortens the construction period, but also avoids the wall. Problems such as cracking will also integrate energy conservation and exterior wall decoration, which has good economic benefits. And the prepared heat-preserving putty material with excellent construction performance, low thermal conductivity, good water resistance and certain strength is beneficial to the promotion of heat-insulating coating system. This article discusses the preparation method of heat-preserving putty and tests the product. The effects of the amount of vitrified microbeads, cellulose ether, and hydrophobic agent on the dry density, thermal conductivity, strength, workability, water absorption and softening coefficient of the product are studied. And get the best formula for building insulation putty.

1 Experiment
1.1 Experimental raw materials
32.5R white cement (25% ~ 60%); redispersible latex powder (1% ~ 3%); hydroxypropyl methyl cellulose ether (viscosity 20W, 0.4% ~ 0.7%); 70 to 100 mesh vitrified microbeads (37% to 75%); wood fibers (0.1% to 0.3%); thixotropic agent (0.05%); silicone water repellent (0 to 0.4%).

1.2 Experimental methods
The experimental water consumption is determined by the optimal water consumption of the thermal insulation putty. The thermal conductivity test is performed with reference to GB / T 10294-2008 “Stable thermal resistance and related characteristics. Protective hot plate method”. The compressive strength and dry density test are performed with reference to GB / T5486-2008 “Test method for inorganic hard insulation products”. The test of softening coefficient and water absorption shall be conducted with reference to GB / T 5480-2008 “Test method for mineral wool and its products”. The rest of the experiments were performed with reference to JG / T 157-2009 “Putty for Exterior Walls of Buildings”.

2 Preparation technology of thermal insulation putty
Because hollow vitrified microbeads are fragile and easily damaged under high-speed stirring, slow mixing is required, so other powders must be mixed first. The preparation process is as follows: Preparation of single-component building thermal insulation putty Process: Firstly add raw materials such as white cement, latex powder, cellulose ether, wood fiber, hydrophobic agent and thixotropic agent into the stirring kettle, stir slowly for 20min, then add hollow glass beads, and stir slowly for 5min.
Preparation technology of experimental putty slurry: First add raw materials such as white cement, latex powder, cellulose ether, wood fiber, water repellent and thixotropic agent to the stirring kettle, and add water at 30% of the powder mass ratio to stir. Stir slowly for 1 min, stir at high speed for 2 min, and then add the hollow vitrified beads and the remaining water to stir slowly for 2 min.

3 Results and discussion
3.1 Determination of the amount of vitrified microbeads
Vitrified microbeads are common inorganic thermal insulation materials. Their thermal conductivity is 0.028 ~ 0.048W (m · K) and bulk density is 50 ~ 200kg / m3. They have the characteristics of light weight, high temperature resistance, sound insulation and heat insulation. The amount of vitrified microbeads must be considered in combination with strength, workability and thermal insulation effect. As shown in Figures 1 and 2, as the proportion of vitrified beads increased, the water demand of the slurry increased significantly, the water-cement ratio increased, and the slurry density and dry density decreased. Compared with ordinary putty (the slurry density is about 2000kg / m3), the construction area of ​​the same quality insulation putty with the same thickness is larger, which is 3 to 4 times that of ordinary putty. As shown in Figure 3, as the proportion of vitrified microbeads increases, the thermal conductivity of thermal insulation putty decreases, and the thermal conductivity decreases significantly in the range of 40% to 55%, and the thermal conductivity of the range of 55% to 70%. The decline in the coefficient is relatively gentle. This is because the heat transfer in the insulation putty is composed of two methods. The main method is heat conduction. The porous structure formed by the vitrified microbeads inside the putty. The internal heat conduction can only be performed between the pore walls, which lengthens the conduction path and reduces the heat conduction. However, if the amount of vitrified microbeads is too much, the water demand will increase, the internal pores will be larger, and the air molecules will have greater flow capacity in the putty layer. Some of them can conduct heat transfer in the form of thermal convection, but increase the heat transfer . Increasing the amount of vitrified microbeads will cause the compressive strength of the material to decrease (as shown in Figure 4), where the amount of vitrified microbeads is greater than 60%, the compressive strength is low and the change is not obvious; Reducing the amount of vitrified microbeads can significantly increase the compressive strength of putty. Therefore, it is necessary to comprehensively consider the mechanical properties and thermal insulation effect, and select the blending amount of 50% ~ 55% as the optimal blending amount of vitrified microbeads.

The effect of the amount of vitrified microbeads on the water demand
Effect of doped amount of vitrified beads on thermal conductivity
Effect of the amount of vitrified beads on the compressive strength of putty

3.2 Determination of cellulose ether content The
modification of thermal insulation putty with polymers can effectively improve the adhesive properties, consistency and workability of putty powder. The effects of hydroxypropyl methylcellulose ether with different viscosity of 20W on the compressive strength, dry density and adhesive strength of thermal putty were tested, as shown in Figure 5 and Table 1. With the increase of cellulose ether content, the compressive strength and bonding strength of the finished product increased significantly, and the dry density remained basically unchanged. On the one hand, due to the large amount of vitrified microbeads in the insulation putty, the strength is very low. The polymer film formed by the cellulose ether inside the material can increase its strength to a certain extent; on the other hand, the cellulose ether has an air-entraining effect and can The introduction of more air bubbles into the putty pulp results in a decrease in strength. The combination of the two effects led to a decrease in the strength of the addition of cellulose ether under the content of high vitrified microbeads, and a slight increase in strength of the addition of cellulose ether under the content of low vitrified microbeads. In addition, cellulose ether can improve the bonding performance of mortar and improve the workability. Considering it comprehensively, 0.5% is selected as the best cellulose ether dosage.

Figure 5 Effect of cellulose ether content on compressive strength of putty under different amounts of vitrified microbeads Table 1 Effect of cellulose ether content on product dry density and bond strength

3.3 Hydrophobic treatment of insulation putty
Unlike ordinary putty, exterior wall insulation putty must be treated with hydrophobic treatment. Because after the water-retaining putty layer absorbs water, water as a heat conductor will reduce the heat-retaining performance, and at the same time its strength and stability will also decrease. At the same time, the too high water-absorbency of the putty layer will not be conducive to the subsequent coating construction. Water repellent treatment is carried out by incorporating silicone water repellent into insulation putty. The effect of the amount of water repellent on the water absorption and softening coefficient of the product is shown in Figure 6 and Figure 7. After the water-repellent agent is added, the water absorption of the product decreases first and then changes little. The water absorption increases significantly after prolonged soaking time. After adding the hydrophobic agent, the softening coefficient of the product slightly increased, but the change was not large. The hydrophobic agent mainly forms a hydrophobic group in the putty by cross-linking, and attaches to the surface of the inner pore wall of the putty. At the same time, it encapsulates the vitrified beads, which can reduce the water absorption of the heat-preserving putty within a certain range, thereby improving the water resistance of the putty layer However, too much mixing will affect the construction of the putty, the improvement of the hydrophobic effect is small, and considering the cost comprehensively, the addition amount can be 0.1%.

Figure 6 Effect of water repellent dosage on water absorption of putty Figure 7 Effect of water repellent dosage on product softening coefficient

4 Conclusion
Through experiments, a formula for heat-preserving putty was obtained, in which the amount of vitrified beads was 50% to 55%, the amount of cellulose ether was 0.5%, and the amount of hydrophobic agent was 0.1%. This product has good workability, its thermal conductivity is less than 0.065W (m · K), its compressive strength reaches 710kPa, the amount of glass beads is increased, the thermal conductivity, dry density and compressive strength of insulation putty are reduced; cellulose ether It can improve the bonding performance of heat-preserving putty, and increase its compressive strength under the low glassy microbead content; adding a hydrophobic agent can effectively reduce the water absorption of the putty layer. Building insulation putty, as a new type of exterior wall insulation material, has both decorative leveling and energy saving functions, and has good development prospects.

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