Detailed explanation of Plaster Retarder
Plaster has been used for centuries as a versatile product in the construction industry. Plaster has a variety of uses and can be used to create decorative plasterwork, functional wall panels, and intricate sculptures. Plaster used to have a dilemma: fast setting. Therefore plaster retarders have become indispensable additives in plaster.
What is a retarding agent for plaster?
A plaster retarder is an additive specifically designed to extend the setting time of plaster. Plaster is mainly composed of gypsum and water. When water is added to gypsum, a chemical reaction is triggered to form a crystal structure. This process is exothermic, i.e., heat is generated. The crystalline structure is the basis for the plaster to harden and perform its function. While this exothermic reaction is critical to the setting of the plaster, it can also create challenges for construction workers in some specialized applications. The problem stems from the speed of the reaction. In some construction scenarios, especially those involving complex designs and large areas, rapid setting can lead to uneven application, making the end result less than desirable. Plaster retarders can solve these challenges by slowing down the setting process and extending the working time.
How does plaster retarder work?
The mechanism behind plaster retarders is to alter the kinetics of the plaster crystallization process. First, when plaster and water are mixed, plaster crystals begin to form. These crystals are part of the plaster matrix. Second, as more crystals form, they grow and interlock, allowing the plaster to solidify gradually. The plaster retarder then intervenes in this process by inhibiting crystal growth. It does this by interfering with the ability of the crystals to grow or by altering the surface properties of the crystals, making it more difficult for them to bond and solidify. Finally, as crystal growth slows down, the setting of the plaster is delayed. The use of plaster retarders allows builders to apply plaster with precision.
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HPMC is used in conjunction with a plaster retarder.
Since plaster can be divided into hard plaster and semi-anhydrous plaster, different types of plaster have different requirements for product properties. Different types of plaster have different requirements for product properties, so the thickening, water retention and retardation properties determine the quality of plaster building materials. Hydroxypropyl methylcellulose (HPMC) has also become a common ingredient in plaster. In some construction projects, using cellulose ether alone as a retarder may not achieve the desired results, such as the appearance of some hollow cracks. To solve this problem, you can use a combination of cellulose and retarder. Kemox suggests that you choose to add hydroxypropyl methylcellulose, the amount of 1.5% to 2%. Hydroxypropyl methylcellulose can improve constructability, reduce shrinkage and cracking, and play a significant water retention, retardation, and lubrication.
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