Many believe that the more cement used for plastering, the stronger it becomes. However, the more cement, the thicker the mortar, the greater the shrinkage of the plaster layer, and the more likely it is to develop more cracks. Generally, when applying a thin layer of cement mortar, it is crucial to avoid using an excessive amount of cement. Be mindful of calcium hydroxide in the cement, as it should not come into contact with acidic corrosive substances, which can cause neutralization reactions, resulting in a loose, expanded volume that is easily hydrolyzed and powdered when in contact with water. This leads to the gradual corrosion and disintegration of concrete or plaster layers, so cement should be avoided from acidic corrosion!
The production of silicate cement is highly representative in the cement production process. It primarily uses limestone and clay as raw materials, which are crushed, mixed, and finely ground to form raw meal. The raw meal is then calcined in a cement kiln to produce clinker. The clinker is subsequently ground with a suitable amount of gypsum (and sometimes mixed materials or additives) to create the final cement. Depending on the method of raw meal preparation, cement can be categorized into dry (including semi-dry) and wet (including semi-wet) processes.
1. Dry production method. This involves drying and grinding the raw materials, or first drying and grinding them into raw meal powder before firing them in a dry kiln to mature. Semi-dry production, also a type of dry production, is a method where raw meal powder is mixed with a certain amount of water to form raw meal balls, which are then sent to the rotary kiln for firing to produce mature material.
2. Wet-process production. A method of producing clinker by feeding raw materials mixed with water into a ball mill to create a raw material slurry, which is then calcined in a wet kiln. Alternatively, the raw material slurry prepared by wet process can be dried and formed into raw material blocks before being calcined in the kiln to produce clinker. This is known as semi-wet process and still falls under the category of wet-process production.
This process primarily involves using fingers to "pulse-check" the cement, distinguishing its duration since production. Cement also has a shelf life; generally, if cement is not used within 30 days of its production, its strength may decrease; after three months, its strength can drop by 10%-20%; and after one year, it may decrease by 25%-40%.
High-quality cement will not exhibit signs of moisture absorption or lumping. When the cement powder is pinched with fingers, a fine, granular feel is noticeable. Poor-quality cement, upon opening, will show signs of moisture absorption and lumping. Pinching the cement powder will result in a coarse sensation. In this case, the cement will not perform normally during use, showing low strength and poor adhesion.
