Dry Mix Mortar Additives Content

The main types of cellulose ethers used in dry mortar are hydroxyethyl methyl cellulose ether (HEMC) and hydroxypropyl methyl cellulose ether (HPMC). Both of these are commonly referred to as MC (short for methyl cellulose).

 

As we all know modern dry mix mortars include various additives that improve performance.

 

Cellulose Ether

 

One of the most common additives is cellulose ether. These are compounds derived from plant fibers and are used in dry mortars to serve as thickeners (substances that increase the viscosity or thickness) and water retention agents (substances that prevent water from evaporating too quickly). Even though cellulose ether only makes up a small portion of the mortar mix (about 0.02% to 0.7%), it plays a crucial role in the mortar's overall performance.

 

The main types of cellulose ethers used in dry mortar are hydroxyethyl methyl cellulose ether (HEMC) and hydroxypropyl methyl cellulose ether (HPMC). Both of these are commonly referred to as MC (short for methyl cellulose). These substances enhance the mortar's adhesion (its ability to stick to surfaces) and workability (how easy it is to apply and shape). For example, when working on vertical surfaces, MC helps prevent the mortar from dripping or sliding down.

 

Moreover, cellulose ethers significantly improve water retention (the mortar's ability to keep moisture), which reduces the chance of the water evaporating too quickly. This property also allows for thinner mortar layers. Additionally, MC extends the open time of the mortar, which is the amount of time the mortar remains usable before it starts setting or drying.

 

 

Redispersible Polymer Powder  

 

When the mortar dries, redispersible polymer powder forms a network structure throughout the material, enhancing the mortar's flexibility, adhesion, and water resistance. This makes the mortar more durable and better suited for various applications.

 

Starch Ether  

 

Starch ethers are used to improve the properties of cement and gypsum-based dry mix mortars. When combined with cellulose ether, starch ether enhances the mortar's workability and improves its performance in application, providing a smoother texture and better application control.

 

Air-Entraining Agent  

 

Air-entraining agents introduce microbubbles into the mortar through physical action, which reduces the overall density of the mortar. This not only improves the workability but also enhances the mortar's resistance to freeze-thaw damage, making it more durable in colder climates. Common air-entraining agents, such as fatty sulfonic acid sodium salt and sodium sulfate salt, are typically added in small amounts ranging from 0.01% to 0.06%.

 

Water-Repellent Agent  

 

When added to dry mortar, water-repellent agents create a hydrophobic surface within the mortar's pores, significantly reducing its water absorption. This helps enhance the durability and moisture resistance of the mortar.

 

Setting Retaining Agent  

 

Setting-retaining agents are used to control the setting time of mortar. They allow for adjustable setting times, which can be essential for specific applications. Calcium formate is a common setting-preserving agent, typically added in proportions ranging from 0.5% to 2.5%.

 

Retarder  

 

Retarders are used to slow down the chemical reaction in cement, extending the setting time of materials like gypsum plasters and gypsum-based caulks. Common retarders include fruit acid salts, which are usually added in small amounts, ranging from 0.05% to 0.25%.

 

Hydrophobic Agent  

 

A hydrophobic agent prevents water penetration while allowing water vapor diffusion through the mortar. Typically, dispersible polymer powders with hydrophobic properties are used. These agents are designed to be rain-resistant and remain effective for many years, significantly extending the service life of the mortar.

 

Defoamer  

 

Defoamers are added to reduce the air content in the mortar. Common defoamers include inorganic carriers with hydrocarbons or polyethylene glycol, which also act in conjunction with other additives like pigments, thickeners, and plasticizers to enhance the mortar's properties.

 

Fibers  

 

Fibers in mortar are categorized into long and short types. Long fibers are primarily used for reinforcement and strengthening, while short fibers are used to improve mortar properties and regulate water demand, contributing to better durability and performance.

 

Superplasticizer  

 

Superplasticizers are essential in self-leveling dry mortars where high fluidity and flowability are required. They enhance the mortar's ability to spread easily without compromising its strength and performance.

 

Thixotropic Lubricants  

 

Thixotropic lubricants improve the thixotropy (the ability to become fluid when agitated and solid when at rest) and lubricity of the mortar. These additives help extend the open time for application and enhance the mortar's anti-sagging properties, making it ideal for use on vertical surfaces without dripping or sliding.