Summary of measures for preventing and controlling cracks in exterior wall insulation.-HPMC

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Cracking in exterior wall insulation is a systemic engineering problem that requires meticulous control throughout the entire process, from design and materials to construction and maintenance. The following are the main preventive measures:

I. Preventive Measures During the Design Phase

1. Systematic Design: Select a complete, proven external insulation system that is compatible with the base wall, insulation layer, rendering layer, and finish layer, avoiding the use of materials from different manufacturers.

2. Structural Design Optimization: Ensure the main structure has sufficient rigidity and stability to reduce structural deformation. Provide special reinforcement designs for stress concentration areas such as cantilevered components and cornices.

3. Detailed Construction Node Design:  Reinforce the design of detailed nodes such as door and window openings, corners, eaves, expansion joints, and through-wall pipes (e.g., adding reinforcing mesh, reserving expansion space), and draw detailed large-scale drawings.

II. Material Selection Control Measures

1. Insulation Material Control: Select boards with good dimensional stability and sufficient curing time. Before bonding, check their density, compressive strength, thermal conductivity, and other indicators to ensure they meet design requirements.

2. Bonding and Rendering Mortar:  Use special mortar that is compatible with the insulation material. Its flexibility, bonding strength, and compression-to-flexural strength ratio should meet crack resistance requirements. The use of ordinary cement mortar is prohibited.

3. Reinforcement Mesh Selection: Alkali-resistant fiberglass mesh or hot-dip galvanized welded steel mesh (for the first floor or tile finishes) must be used in the rendering layer. The mesh weight, alkali-resistant tensile strength, and retention rate must be qualified.

4. Finish Material Matching: For paint finishes, use flexible waterproof putty and elastic paint or multi-layer textured paint with good crack resistance; for tile finishes, use flexible adhesives and grouting agents.

III. Key Control Measures During Construction

1. Substrate Treatment: Before construction, the wall substrate must be thoroughly cleaned to ensure it is flat, firm, free of voids, oil stains, and release agents. Interface treatment should be performed if necessary.

2. Adhesive Application: The insulation boards should be bonded using the full-coverage method or strip bonding method to ensure that the effective bonding area meets the specifications. The boards should be tightly joined, and any height differences should be sanded smooth. A staggered arrangement should be used to avoid continuous joints.

3. Anchor Bolt Reinforcement: Anchor bolts should be installed strictly according to the design requirements for location and quantity, ensuring reliable anchoring into the substrate wall. The anchor bolt plates should be pressed firmly against the insulation board, but not excessively.

4. Surface Layer Construction (Key Anti-Cracking Layer):

* Layered Construction: Strictly follow the process of "one base layer, one layer of embedded reinforcing mesh, and one surface layer." The base mortar thickness should be appropriate, and the reinforcing mesh should be immediately pressed into it.

* Mesh Laying: The mesh should be laid flat without wrinkles. The standard mesh overlap width should be no less than 100mm, and the reinforcing mesh should be butt-jointed. Reinforcing mesh of 300mm × 400mm should be added at the four corners of door and window openings along the 45° direction.

* Curing: After the surface layer construction, avoid rain and direct sunlight before drying, and perform necessary watering and curing to prevent rapid drying shrinkage and cracking.

5. Environmental Control: The construction environment and substrate temperature should be between 5℃ and 35℃, and construction should be avoided in adverse weather conditions such as high temperatures, strong winds, and rain.

IV. Usage and Maintenance Measures

1. Finished Product Protection: After construction, avoid hanging heavy objects on the exterior wall or subjecting it to severe impact. Subsequent installation of plumbing, electrical, and air conditioning systems should be carried out according to specifications to prevent damage to the insulation layer.

2. Regular Inspection and Maintenance: After the building is put into use, the exterior walls should be inspected regularly. Any minor cracks, voids, or other defects should be repaired promptly by professional personnel to prevent moisture intrusion, which can lead to crack propagation and insulation failure. Summary

Preventing cracks in exterior wall insulation systems hinges on "system compatibility, meticulous design, qualified materials, and standardized construction." It is crucial to abandon the erroneous practices of prioritizing materials over the system, focusing on the main structure while neglecting details, and rushing construction at the expense of proper curing. Only through comprehensive and meticulous management throughout the entire process can the durability and crack resistance of exterior insulation systems be effectively improved.