The Role And Key Points Of Construction Application Of Alkali-resistant Fiberglass Mesh in External Wall Insulation Systems

External wall insulation systems are a crucial component of building energy conservation and wall protection. The crack-resistant plaster layer, as a key line of defense in the insulation system, directly determines whether common quality problems such as hollowing, cracking, and water seepage will occur in the external wall later on. Alkali-resistant fiberglass mesh is an indispensable reinforcing material in the crack-resistant protective layer, relying on its excellent tensile and crack-resistant properties to ensure the long-term stable operation of the external wall insulation system.

 

I. Interpretation of Relevant National Technical Standards

 

My country has issued two important industry standards for fiberglass mesh for external wall insulation. The requirements of the two standards differ significantly. When selecting materials for a project, the applicable standard should be distinguished, and the appropriate type should be selected according to the needs.

 

According to JG149-2003 "Expanded Polystyrene Board Thin Plaster External Wall Insulation System": The alkali-resistant tensile breaking strength of the fiberglass mesh in both the warp and weft directions shall not be less than 750N/50mm, the alkali-resistant tensile breaking strength retention rate shall not be less than 50%, and the weight per square meter shall be ≥130g.

 

According to JG158-2004 "External Wall Insulation System with Adhesive Powdered Polystyrene Granules": the alkali-resistant tensile breaking strength of fiberglass mesh in both the warp and weft directions shall not be less than 1250 N/50 mm, the alkali-resistant tensile breaking strength retention rate shall not be less than 90%, and the weight per square meter shall be ≥160 g.

 

In contrast, most external wall insulation mesh fabrics currently circulating in the building materials market have an areal density of around 160 g/㎡, but their mechanical strength is generally low, with a normal breaking strength of only 1000 N/50 mm or even lower, posing a risk of substandard material specifications. Therefore, in external wall insulation projects, the technical parameters of the mesh fabric must be standardized and controlled. After the materials arrive on site and before formal construction, the purchased alkali-resistant fiberglass mesh fabric must be inspected to ensure that all performance indicators are qualified before it can be used.

 

Preventing external wall cracks is a systematic task. Not only do the insulation layer materials need to have qualified tensile strength and ultimate elongation, but the outer crack-resistant protective layer also needs sufficient tensile strength as a guarantee. This means that when purchasing alkali-resistant fiberglass mesh, tensile strength and alkali retention rate must be the two core indicators that need to be carefully checked; weight alone cannot be ignored while mechanical properties are taken into account.

 

II. Crack-Resistant Mechanism of Alkali-Resistant Fiberglass Mesh

 

Embedding alkali-resistant fiberglass mesh into plastering mortar can improve the quality of the protective layer in two dimensions.

 

First, it effectively increases the overall tensile strength of the plastering protective layer, compensating for the weakness of cement mortar in tensile strength.

 

Second, the mesh can evenly disperse the internal stress generated in the wall, breaking down wide cracks that are prone to appearing in the wall into multiple fine, harmless cracks, thereby inhibiting crack propagation and achieving crack resistance in the wall.

 

The long-term alkali resistance of the mesh is determined by two main factors. The type of fiberglass substrate is the fundamental factor determining long-term alkali resistance and durability; the coating material on the surface of the mesh and the amount of sizing applied play a crucial role in the short-term alkali resistance of the fiberglass mesh. Both are indispensable. Only with a qualified substrate and proper coating can the mesh fabric maintain its strength in an alkaline mortar environment and avoid premature powdering and failure.

 

III. Key Points of On-site Construction and Laying Technology

 

Correct construction techniques are crucial for the mesh fabric to achieve its crack-resistant reinforcement effect. The following operational requirements should be observed during on-site construction:

Overlap Width:

The horizontal overlap width between mesh fabrics should not be less than 100mm; at internal corners, the mesh fabric should be overlapped with a ≥100mm overlap width; at external corners, the overlap width should also be no less than 100mm to ensure continuous reinforcement at corners.

 

Laying Quality:

The mesh fabric should be laid flat, without wrinkles or curling edges; the mortar fullness should reach 100%. After construction, it should be smoothed and straightened promptly to ensure that the internal and external corners of the wall are square and the verticality meets specifications.

 

First Floor Reinforcement:

It is recommended to use 240g double-layer mesh fabric to reinforce the exterior walls of the first floor of the building to improve the impact resistance and crack resistance of the underlying wall.

 

Diagonal Reinforcement of Openings: At the four corners of door and window openings, add 45° diagonal reinforcing mesh to distribute stress at the corners and prevent herringbone cracks.

 

Fireproof Barrier Overlap: The overlap length between the fireproof barrier mesh and the main wall mesh should be ≥100mm to ensure the integrity of the insulation system.

 

Overlap Treatment

At the termination points of the insulation system, the overlap size of the alkali-resistant mesh should be no less than 100mm to ensure proper end sealing and reduce the risk of edge cracking and water seepage.

 

Conclusion

Although alkali-resistant fiberglass mesh is only an auxiliary material in the external wall insulation system, it plays a crucial role in crack prevention. During the project, it is essential to strictly control the material's incoming specifications, verifying the basis weight, tensile strength, and alkali resistance retention rate against the standards; and to strictly implement construction details such as overlapping, reinforcing mesh, and overlap. Only by meeting material standards and adhering to standardized construction can the risk of external wall cracking be reduced from the source, the service life of the external wall insulation project be extended, and long-term stable energy conservation in buildings be achieved.