Glass yarn should be used to prevent cracking of external insulation system

1. Breaking strength and alkali resistance strength retention rate

Breaking strength and alkali resistance strength retention rate are important properties of glass yarn. Breaking strength is inseparable from glass count or weight. At present, the glass yarn used for exterior wall insulation systems on the Chinese market generally weighs about 130g per square meter, and its strength is generally low. Its normal breaking strength is only about 1000N/5cm. In Europe or the United States, where exterior wall insulation technology and regulations are relatively mature, the requirements for the breaking strength of Fiber Glass are much higher than in my country. The German Building Technology Board (DIBt) requires that the normal breaking strength of glass yarn used for exterior wall insulation systems is ≧1750N/5cm, and the alkali resistance retention rate is ≧50%. If domestic products meet this requirement, the weight of glass yarn per square meter must be above 160g.

Improving breaking strength standards is undoubtedly necessary. Especially polymer cement plaster mortar with higher cement content and cement strength grade. The damage caused by these things to the Fiber Glass is not only chemical corrosion, but also the crystallization pressure corrosion of calcium hydroxide and calcium sulfoaluminate. At the same time, the high water absorption rate of mineral materials also has a negative impact on the glass yarn. Experiments have shown that after soaking in distilled water, the strength of the Fiber Glass will be lost by about 30%.
Our country currently lacks standards for glass yarn specifically used for exterior wall insulation systems, especially the alkali-resistant strength retention rate and alkali-resistant test methods. The alkali solutions used by testing agencies or manufacturers in various places vary, and NaOH solutions are used. There are 80℃ cement slurry and NaOH, KOH, Ca(OH)2 mixed alkali solution. Since the formulation of this performance index has a great impact on the performance trend, price, and market affordability of products on the market, relevant research units must conduct a unified investigation of the performance of domestic Fiber Glass, refer to foreign standards, and formulate Standards suitable for our country`s national conditions.
Cement-free pure polymer plastering mortar has no alkali corrosion and low water absorption. The glass yarn can function normally in it for a long time, which is undoubtedly the safest for the long-term crack resistance of the protective surface layer.
2. Fiber Glass and plastering glue should be closely related
When subjected to tensile deformation, the plastering glue must work in harmony with the glass yarn. The two materials must have a good correlation. No matter how high the strength is, cracks will still occur in the grid cloth that has a poor correlation with the plastering glue. Produced in the early stages.
When the protective surface layer begins to bear tensile force, the glass yarn should be in a stressed state as soon as possible to exert its tensile properties and disperse the stress. Although the glass yarn 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 and 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.
In Europe and the United States, it is generally believed that cracks with a width of less than 0.2mm are harmless cracks. For the external wall insulation system, the more important thing is not to prevent the occurrence of cracks (just like steel bars cannot prevent the cracking of concrete, whether the plaster mortar eventually cracks depends on its cracking strain), but to delay the deformation time as much as possible, thereby delaying cracking. , while limiting the width of a single crack.