The Science Behind Liquid Screed: What Makes It Flow, Set, and Last
The Science Behind Liquid Screed: What Makes It Flow, Set, and Last
Liquid screed is transforming the flooring industry — and it’s not just because of its speed and finish. What truly sets it apart is the science behind its performance: a careful balance of materials, chemistry, and engineering that enables it to flow easily, set quickly, and provide long-lasting durability.
In this article, we dive into the materials and processes that power liquid screed, and explore why it’s such a reliable choice for modern construction projects.
🧪 1. What Is Liquid Screed Made Of?
Liquid screed — also known as flow screed — is typically composed of:
Gypsum-based binder (calcium sulphate hemihydrate)
Fine sand or filler aggregate
Water
Plasticisers or superplasticisers
Unlike traditional screed, which uses cement as a binder, liquid screed primarily uses anhydrite (a form of calcium sulphate). This key difference in binder chemistry is what gives liquid screed its self-levelling and fast-setting properties.
🌊 2. What Makes It Flow So Easily?
The flowability of liquid screed comes from two main factors:
a. Particle Size Distribution
Liquid screed uses finer aggregates than traditional sand and cement mixes.
These fine particles reduce internal friction, allowing the mixture to spread evenly with little to no manual levelling.
b. Use of Superplasticisers
Chemical additives are added to reduce the water content without compromising flow.
These polymers help disperse particles evenly, giving the screed a free-flowing consistency while maintaining strength and density.
➕ Result: The screed naturally finds its level, reducing labour and achieving a flat surface with minimal intervention.
🔗 3. How Does It Set? The Hydration Process
The setting process in liquid screed is based on hydration chemistry — but not of cement. Instead, it involves:
Calcium sulphate hemihydrate reacting with water to form calcium sulphate dihydrate (commonly known as gypsum).
This reaction creates interlocking needle-like crystals that bind the mixture together.
Key Differences from Cement:
Lower heat of hydration – meaning fewer thermal stresses and less cracking.
More consistent curing – the chemical reaction is controlled and predictable.
Faster walk-on time – usually within 24–48 hours.
🔬 4. What Gives It Long-Term Durability?
Although liquid screed is more fluid, it doesn't compromise on strength. In fact, it often outperforms traditional screeds in structural integrity and longevity due to:
a. High Compressive Strength
Typical compressive strengths of 25–40 N/mm², suitable for residential and commercial use.
b. Minimal Shrinkage
The chemical setting process generates less movement, which means fewer surface cracks and long-term stability.
c. Dense Microstructure
The fine aggregates and tight particle packing result in a smooth, dense surface with low permeability.
d. Efficient Thermal Conductivity
Ideal for underfloor heating — the screed fully encapsulates heating pipes and facilitates even heat transfer.
🏗️ 5. Why It Lasts in Real-World Conditions
The longevity of liquid screed isn't just about chemistry — it’s also about how well it performs in the field:
Resistant to thermal cycling (expansion/contraction from heating systems)
Consistent performance across large areas
Non-reactive to most floor adhesives once properly sanded
Low maintenance after installation
With correct installation and post-care, liquid screed can easily last decades without cracking, delaminating, or deteriorating — especially in modern, energy-efficient buildings.
⚠️ Important Considerations
To get the most from liquid screed, it’s essential to:
Sand the surface (laitance removal) before applying adhesives or tiles
Ensure correct drying time and environmental conditions
Use appropriate primers/sealers in high-moisture areas
