The importance of the correlation between fiberglass mesh and plastering glue
When subjected to tensile deformation, the plastering glue must work in harmony with the fiberglass mesh cloth. The two materials must have a good correlation. No matter how high the strength of the mesh cloth is that is not well correlated with the plastering glue, it will still be strong. Cracks will inevitably occur in the early stages. When the protective surface layer begins to bear tensile force, the mesh cloth should be in a stressed state as soon as possible to exert its tensile properties and disperse the stress. Although the mesh cloth cannot prevent the plaster mortar from producing the first crack when it reaches a certain tensile strain, it can effectively delay the development time of the first crack limit the width of the first crack, and pass its longitude and latitude directions. The nodes distribute stress so that the entire plaster mortar is evenly stressed and cracks are evenly distributed.
For this reason, the mesh cloth that has a good correlation with the plastering glue should have the following properties:
1. With higher node strength, if the nodes slip when the mesh cloth is stretched, the stress will be mostly borne by the plastering glue in the initial stage of stress, causing cracks.
The test method for node strength is: to cut along the weft direction
For a 330mm×50mm test strip (the number of weft yarns must be odd), cut off all the yarns on both sides about 150mm from the end of the test strip (need to be cut in the center of the node), leaving only one weft yarn in the middle; After 50mm (or 6 nodes apart), cut the weft yarn in the center. Put the test strip on the tensile machine for a tensile test. One end of the testing machine clamps the weft yarn in the middle, and the other end clamps all the yarns. Read the force of pulling out the yarns (N). Requirements for fiberglass for exterior wall insulation systems The node strength of mesh cloth is ≧3.2N/single wire.
2. Low tensile strain, if the nodes do not slip when the mesh cloth is stretched, but the tensile strain is large, it will also cause the plastering glue to crack in the early stage. The tensile strain of fiberglass mesh includes the strain in the early stage of tension and the strain during cracking. It can be expressed by the tensile force when the elongation is 0.25%, 0.5%, and 1.0%; as well as the tensile force (breaking strength) and breaking strain at break. The external wall insulation system requires the tensile strain of the fiberglass mesh to meet the following requirements:
Tensile force at 0.25% strain ≧150N/5cm,
Tensile force at 0.50% strain ≧300N/5cm
Tensile force at 1.00% strain ≧600N/5cm
Tensile force at break (breaking strength) ≧1750N/5cm
Breaking strain ≦3.5%
3. Mesh fabrics with smaller yarn deflection will inevitably have yarn deviation during weaving. If it deviates too much, it will cause eccentricity when force is applied, which will also affect the use effect. Generally speaking, within a length of 1m, the deflection of the woven wires shall not exceed 3 woven wires.
In summary, the tension-strain curve of a fiberglass mesh that meets the above three requirements should have a linear relationship, as shown in the figure below. The tensile strain of the mesh cloth with a nonlinear relationship in the figure is greater than that of the mesh cloth with a linear relationship under the same tensile force T. Within this deformation range, the plastering glue that works with it may have cracked!
