Gypsum is one of the three main materials in the field of building materials. Gypsum mortar and gypsum building materials are green prefabricated building materials strongly advocated by the country and building material products that are promoted by the country. The use of it not only has the strength of cement, but also healthier than cement, more environmentally friendly, more economical, more durable, strong adhesion, not easy to pulverize, no cracking, no hollowing, no powder and other advantages, easy to use and save cost.
Because the cement-based material itself is a hydraulic and brittle shrinkage material, it has poor water retention. As a result, the bonding strength between the stucco layer and the wall is low, and there are many quality problems such as hollow cracking, shelling and even peeling. When the construction is not standardized, this is more likely to happen, resulting in a higher on-site maintenance rate. The apparent quality and use function of the building are seriously affected. Gypsum plaster, with its good physical and mechanical properties and construction operation performance, has been widely recognized and used in the market, and is the first choice of developers, contractors and construction units.
Compared with the traditional cement plaster, plaster plaster has the characteristics of low shrinkage, early strength and fast hardening, good sound insulation effect, energy saving and environmental protection. In recent years, ordinary plastering gypsum has been in the ascendant, and it has gradually replaced cement plastering in many applications. Lightweight plastering gypsum also shows an increasingly broad market prospect.
The scope of application of plastering plaster: it is suitable for all kinds of brick walls, concrete walls, block walls, cement walls (boards), cast-in-place concrete walls, fabricated interior partition walls and inner walls of all kinds of brick walls, concrete walls, block walls, Plastering and repairing of the ceiling. Both mechanical spraying and manual operation are acceptable.
No matter what kind of plastering gypsum, cracking is a frequently encountered problem, which can be roughly divided into two categories: cracking caused by gypsum quality problems; cracking caused by too fast water loss.
1. Cracking caused by gypsum quality problems At present, the commonly used construction gypsum belongs to hemihydrate gypsum in terms of chemical composition, and most of it is made by calcining and dehydrating the by-product gypsum of dihydrate industry. In most cases, a small part of hemihydrate gypsum will continue to be dehydrated at the calcination temperature, resulting in unstable AIII. The normal hydration process of plastering gypsum should be HH to produce DH, but when the content of AIII phase is high, the hydration step of AIII and HH is inconsistent, the stress generated is inconsistent, and shallower cracks will occur after construction.
2. Cracking caused by too fast water loss The water content of plastering gypsum slurry directly affects the hydration of gypsum. When the water loss is too fast, the gypsum is often hydrated incompletely and unevenly, resulting in cracking.
Excessive water loss is often caused by a combination of many factors, the common ones are the following:
1. Water absorption of the base layer. The rougher the base layer, the more pores and cracks and the stronger the water absorption.
2. During construction, the temperature is high and the wind is strong, causing the moisture to evaporate too fast.
3. The bottom layer is too thin, even if the bottom layer is not strong, it will lose water quickly under the dual influence of bottom layer water absorption and surface evaporation.
4. If the content of cellulose ether is too low or the quality is poor, the water retention will decrease rapidly at high temperature, causing the slurry to lose water. For cracks caused by gypsum quality problems, the preventive suggestion is to do a good job of aging the gypsum. Aging is divided into natural aging and forced aging. The principle of both is to allow AIII in gypsum raw materials to react with moisture in the air to generate HH.
For the cracked wall that has been constructed, the remedial measure is to spray a thin layer of plaster on the surface (if the surface is not dry, apply it directly) to fill the cracks.
For the cracking caused by too fast water loss, it must be solved comprehensively from three aspects: the base, the powder and the construction.
1. For the base layer, it is recommended to use an interface agent to reduce the porosity of the plaster contact surface and improve the sealability.
2. For powder, it is necessary to use cellulose ether with high temperature resistance and high water retention rate. The consequences of using inferior cellulose ether are disastrous.
3. In construction, for the untreated base layer, after cleaning the floating ash, spraying water to moisten the plastering plaster again, the plaster should not be too thin or too thick, otherwise it will increase the risk of cracking.
Post time: Jan-14-2021