When it comes to choosing the right screed for your project, the debate often comes down to two main types: anhydrite screeds and cement-based screeds. Each offers distinct advantages depending on the environment, project timeline, and the desired finish. While both serve the fundamental role of providing a level surface ready to receive floor coverings, the material you choose can significantly impact the programme, performance, and long-term success of the floor.
So, how do you decide which is best? Let’s break it down.
What Are Anhydrite Screeds?
Anhydrite screeds are based on calcium sulphate rather than Portland cement. They are most commonly supplied as flowing screeds, delivered to site ready to pump into place. This makes them ideal for large-scale projects as well as smaller projects.
Key features:
- Self-levelling and self-compacting
- Fast installation – up to 2,000 m²/day
- Lower shrinkage and minimal cracking
- Typically walkable in 24–48 hours
What Are Cement-Based Screeds?
Cement-based screeds are the traditional choice and can be either site-mixed (sand and cement) or proprietary mixes, which include additives for improved performance.
They can be:
- Semi-dry, hand-applied and compacted
- Flowing for pump application
- Fast-drying or fibre-reinforced, depending on specification
Key features:
- Versatile and widely understood on site
- Compatible with almost all adhesives and finishes
- Available in fast-drying formulations
- More forgiving when exposed to moisture
Comparing Key Performance Areas
- Installation Speed
FLowing anhydrite screeds are known for their rapid installation. They can be poured and levelled across large areas in a short timeframe with a small crew. They also offer self-levelling properties, reducing manual labour and producing a smooth, flat finish.
Cement screeds, particularly traditional semi-dry mixes, are slower to apply and require skilled labour. However, flowing cement-based screeds now offer faster application similar to anhydrite.
- Drying Time
Despite quick installation, standard anhydrite screeds can take longer to dry than you might expect – often 60 to 90 days for 50mm thickness under typical site conditions. Drying is purely by evaporation, so poor ventilation or cool temperatures can significantly delay follow-on trades. However, the right conditions can be vital to reducing drying times.
In contrast, fast-drying cement-based screeds can reach moisture levels suitable for floor coverings in as little as 7–14 days, even at standard thicknesses. This makes them ideal for time-sensitive projects.
- Moisture and Adhesive Compatibility
Anhydrite screeds are sensitive to moisture and require strict moisture testing before finishes are applied – especially timber, vinyl or resin. They also need laitance removal (a light sanding) before adhesive can bond properly.
Not all adhesives are compatible with calcium sulphate – many cement-based or reactive adhesives can trigger a failure. Always check with the supplier and use the correct primer.
Cement-based screeds are more universally compatible with adhesives and finishes, and generally pose fewer issues in terms of moisture resistance, especially once dry.
- Strength and Durability
Both screeds can achieve high compressive and flexural strength when specified correctly. For heavy-duty floors, such as commercial units or warehouses, high-performance versions of each type are available.
Cement-based screeds can be tailored with fibres or additives to enhance impact resistance and strength.
- Underfloor Heating Compatibility
Because of their excellent thermal conductivity and self-compacting nature, flowing anhydrite screeds are particularly well-suited to underfloor heating systems. They envelop pipework easily and reduce air pockets, which can improve heat transfer efficiency. That said, modern cement-based flowing screeds can perform similarly.
- Environmental Considerations
Anhydrite screeds are often made from industrial by-products, such as flue gas desulphurisation (FGD) gypsum, making them a more sustainable option. They also have lower embodied CO₂ than Portland cement. However, the sustainability values of screed depend on many other factors, such as longevity and recyclability.
Conclusion
There’s no one-size-fits-all answer — both screeds have a valid place in modern construction. For large, open-plan spaces with tight labour constraints, anhydrite screeds can save time and improve surface quality. But if you’re working to a compressed programme or in a moisture-prone environment, fast-drying cement-based screeds often come out on top.
Whatever you choose, the key is to involve your screed supplier early, match the specification to your project needs, and always follow best practice when it comes to drying, testing and finishing.
