Self Leveling Compounds Additives for Crack-Resistant Mortar Systems

Self leveling compounds are widely used to create flat, smooth substrates before installing tile, vinyl, wood, or decorative coatings. When the formulation is not optimized, problems like self leveling compound cracking, edge curling, pinholes, or dusting can appear very quickly on site. The right additives in the mortar system are a practical way to improve flow, reduce defects, and keep performance stable in different climates.

At TJCY, we supply a full package of construction additives that can be combined to match different cement types, aggregates, and jobsite conditions in self leveling mortars.

Why self leveling compounds crack

Cracking in self leveling compounds usually has several overlapping reasons:

1. Water loss is too fast – high temperature, wind, or absorbent substrates pull water out of the mortar, leading to plastic shrinkage cracks.

   
   

2. Segregation and bleeding – if the paste is too “thin”, fines and water move to the surface while sand settles, creating weak zones.

   
   

3. Improper strength build-up – lack of control over setting and early strength can cause internal stresses and self leveling compound cracking, especially in thicker pours.

   
   

4. Compatibility issues – substrates with poor bonding or high movement can transfer stress into the self leveling layer.

Additives are used to control water retention, viscosity, flow, and curing so that the system can level well and resist cracking.

Core additives for self leveling compounds

Below is a summary of typical additive types and how they contribute to self leveling mortars:

The exact combination depends on flow requirements, layer thickness, substrate type, and climate, but most self leveling compounds use several of these groups together.

Water retention agents: HPMC and HEC

Hydroxy Propyl Methyl Cellulose (HPMC) and Hydroxyethyl Cellulose (HEC) are central to modern self leveling compounds:

• They hold water in the mortar so cement can hydrate evenly.

  
  

• They improve flow and leveling without causing segregation.

  
  

• By slowing early water loss, they help reduce plastic shrinkage and surface cracking.

  
  

• They also improve pumpability and reduce segregation during transport and placement.

For hot or dry conditions, a slightly higher dosage or a grade with stronger water retention is often used. At TJCY Industrial Chemical, different viscosity and substitution grades of HPMC and HEC can be selected according to desired flow time and setting profile.

Water reducing agents: improving flow without extra water

Traditional self leveling mixes often add too much water to get a “nice” flow, which increases the risk of cracking and dusting. A water reducing agent, such as Sodium Lignin Sulfonate, helps:

Achieve the same or better flow at lower water–cement ratio

Increase strength and surface hardness

Reduce shrinkage and improve long-term durability

In self leveling compounds, lignosulfonate-type plasticizers can also help control set time and reduce the tendency for early self leveling compound cracking, as long as they are balanced correctly with the cellulose ether and binder system.

Thickeners and rheology modifiers: Bentonite and Fumed Silica

A good self leveling compound should flow easily when mixed or spread, but should not segregate or bleed once it is at rest. Here, Bentonite and Fumed Silica play supporting roles:

Bentonite acts as a mineral thickener. It improves the yield value and helps keep aggregates suspended, reducing sedimentation and bleeding water.

Fumed Silica works as a fine thixotropic agent. In small dosages it stabilizes the paste, improves edge stability near terminations, and helps to minimize surface defects while still allowing good flow when the mix is agitated.

By tuning these rheology modifiers with your cellulose ether choice, you can design a mortar that is both self-leveling and stable.

Functional fillers and durability additives

Self leveling compounds also rely on well-graded fillers and targeted durability additives:

Silica Powder is a key functional filler that improves packing density, compressive strength, and surface smoothness. It also supports abrasion resistance in high-traffic floors.

Zinc Oxide and other antifungal/antibacterial agents are often used where moisture and organic contamination are concerns, such as basements, food processing or healthcare areas. They help maintain long-term appearance and hygiene.

Sodium Silicate or Ferric Chloride can be used in some systems to increase surface densification and improve water resistance, especially when the self leveling layer serves as the final wearing surface.

These materials are especially useful when the leveling compound is expected to perform more than just a basic “underlayment” role.