What additives are in dry mix mortar?

When it comes to dry mix mortar, many people think of it as a simple mixture of cement, sand and water, but it’s actually much more than that. Modern dry mix mortars have a variety of additive components.

Cellulose ether Cellulose ethers are one of the most common additives used in dry mortars. Cellulose ethers are used as thickeners and water retention agents. Although the proportion of cellulose ether is very low (0.02%-0.7%), it plays a very important role. The cellulose ethers used in dry mortar are mainly hydroxyethyl methyl cellulose ether (HEMC) and hydroxypropyl methyl cellulose ether (HPMC), abbreviated as MC. The adhesion and workability of MC are two interacting factors that make it less prone to dripping or sinking when working on vertical surfaces. Its water retention prevents rapid evaporation of water, enabling the thickness of the mortar layer to be significantly reduced. Cellulose ethers also help to prolong the open time of the mortar (the time for which the mortar remains workable).

Redispersible polymer powder When the mortar dries, the redispersible polymer powder forms a network throughout the material, which enhances the mortar’s flexibility, adhesion and water resistance.

Starch ether Starch ethers improve the properties of cement and gypsum based dry mix mortars. Starch ether should be used in combination with cellulose ether.

Air-entraining agent Introduces microbubbles in the mortar by physical action, reduces the density of the mortar, improves the resistance of the mortar to freeze-thaw damage and better workability. In the fat sulfonic acid sodium salt and sodium sulfate salt add proportion is 0.01%-0.06%.

Water-repellent agent When added to dry mortar, hydrophobic additives form a hydrophobic (water-repellent) surface in the pores of the mortar, which can greatly reduce water absorption.

Setting retaining agent The desired setting time can be obtained with a setting-preserving agent. It is commonly used in calcium formate, and the proportion added is 0.5%-2.5%.

Retarder Retarders slow down the chemical reaction in cement and are mainly used in gypsum plasters and gypsum-based caulks. Mainly fruit acid salts, usually at 0.05%-0.25%.

Hydrophobic agent Prevents water from penetrating into the mortar while the mortar remains open for water vapour diffusion. Mainly dispersible polymer powders with hydrophobic properties are used, characterized by the fact that they will not be washed out of the mortar by rainwater even after many years, with the advantage of significantly longer service life.

Defoamer Used to reduce the air content in mortar. Mainly used in inorganic carriers on hydrocarbons, polyethylene glycol and other additives are pigments, thickeners, plasticizers and so on.

Fibers Fibers are divided into long and short fibers. Long fibers are mainly used for reinforcement and strengthening; short fibers are used to influence the improvement of mortar properties and water requirements.

Superplasticiser Used in self-leveling dry mortars with high requirements.

Thixotropic lubricants Improve the thixotropy and lubricity of the mortar, prolonging the open time of the construction as well as the anti-sagging properties.

Article source: What additives are in dry mix mortar?