What is dry mortar additives?

June 9, 2021
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What is dry mortar additives?


Dry mortar generally uses Portland cement as the cementing material, and the amount of cementing material generally accounts for 20% to 40% of the dry powder mortar; most of the fine aggregate is quartz sand, and the amount is large, and it generally needs to be dried and screened. Graded pretreatment to ensure that its particle size and quality meet the requirements of the formula; sometimes fly ash, slag powder, etc. are added as admixtures. Dry powder mortar additives are generally used in a small amount, about 1% to 3%, but they have great effects. They are often selected according to the requirements of the product formulation to improve the workability, delamination, strength, shrinkage and frost resistance of the mortar.


Types of dry mortar additives:


1.​Cellulose ether


Cellulose ethers of different viscosities have different uses. For example, those with the prefix "carboxyl" are very cheap, and can be used in low-grade putty powder for interior walls to thicken and retain water and increase leveling. Hydorxypropyl Methylcellulose(HPMC) is chemically stable, can prevent mildew, have a good water retention effect, and are not affected by changes in pH. The viscosity generally be used is from 50,000 to 200,000. Cellulose ether is bused to increase the leveling and construction properties of dry mortar, and appropriately reduce the amount of cement.



2.Redispersible polymer powder


Redispersible polymer powder is a special high molecular polymer powder made after spray drying. After the powder comes into contact with water, it can become an emulsion again, and has the same properties as an emulsion. After the water evaporates, it can form a film. The film has high flexibility, high weather resistance, and high adhesion to various base layers.

Therefore, it is an indispensable raw material in dry-mixed mortar, which can improve performance and strength, improve the bonding of dry-mixed mortar with various substrates, and improve the flexibility, compressive strength, and abrasion resistance of dry-mixed mortar. In addition, If mixed with water-repellent latex powder, it can make the dry mortar waterproof.


In addition, cement mortar has a solidification period, during which it needs artificial curing to keep it moist. Due to the water retention of cellulose ether, the water required for mortar coagulation can be obtained from the water retention of cellulose ether, so it can be coagulated without special maintenance.



The role of lignin in dry mortar is to resist cracking. When lignin is dispersed in water, it is in the form of short fibers. For example, when building walls with soil in China, wheat straw and rice straw are added to resist cracking. When using lignin, it is best to choose pure materials without impurities. When identifying lignin, you can turn the lignin to see if there is any dust left. The more the powder, the worse the quality. Or put a little lignin into the water to observe, the better the dispersibility, the better the quality, which shows that if it is added to dry mortar, it is also easy to disperse and will not form a mass.




4.Inorganic bonding material

Gray calcium powder is calcium hydroxide, a commonly used inorganic binding material. It mainly play a binding role in the putty powder to achieve waterproof and water-resistant effects. There are many domestic limestone producing areas, so the production of lime-calcium powder is more common. But in some places, the putty mortar made of lime-calcium powder can burn off the skin during construction. This is because the proportion of water added to the production of lime-calcium powder is low, and the content of quicklime is high. When you encounter sweat on your hands, you will get up immediately. Exothermic reaction, so the draft of gray calcium powder is large and alkaline. The larger the draught, the more unstable it is. It is easy to crack when scratched on the wall. We need to look for a material with more stable gray calcium powder, which has a small draught, good whiteness, and does not erode hands.