Screed chemistry explained
Calcium Sulphate vs Cement Screed: The Chemistry
Every liquid screed on the market is either calcium-sulphate or cement-based. That one fact decides more about your floor than any brand name does.
Get the chemistry right first time
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Brands like Cemfloor, Gyvlon and Gypsol get discussed as if they're competing products doing the same job. Strip away the branding and there are really only two chemistries: calcium sulphate (anhydrite) and Portland cement. Every practical difference you'll read about — sanding, wet-room suitability, tile compatibility, drying rate — comes down to which of these two a given product is.
Understanding the chemistry rather than the brand names means you can specify correctly even when a supplier substitutes one product for another of the same type.
This page is the chemistry primer we send to architects and self-builders before the brand conversation even starts.
Calcium sulphate vs cement — the chemistry
| Factor | Calcium sulphate / Cement |
|---|---|
| Binder | Gypsum-derived anhydrite / Portland cement |
| Water sensitivity | Degrades with repeated saturation / Stable when wet |
| Surface laitance | Forms, must be sanded before adhesives / Minimal, rarely needs sanding |
| Shrinkage | Very low / Low but slightly higher than anhydrite |
| Typical brands | Gyvlon, Gypsol / Cemfloor |
Why the chemistry decides tile adhesive choice
- Cement-based adhesives bond naturally to a cement screed
- Anhydrite screeds need a primer to isolate the gypsum surface before cement-based adhesive is used
- Getting this step wrong is one of the most common causes of tile debonding on new floors
- Cement screeds are compatible with epoxy and resin coatings without special isolation
Get the chemistry right first time
Tell us what's going in each room and we'll confirm the correct screed chemistry before we quote a single product name.
Why this isn't just semantics
We've surveyed floors where a specifier wrote 'liquid screed' on the drawings without naming a chemistry, and the installer defaulted to whichever was cheapest that week. In a dry bedroom, that's harmless. In a wet room or under a resin floor, it can mean a full floor replacement within a couple of years.
If you only remember one rule: cement chemistry for anywhere water touches the floor repeatedly, calcium sulphate for everywhere else where cost and UFH thermal performance matter more.
Calcium sulphate vs cement: the decision test
Choose calcium sulphate when…
- The build is dry throughout — no wet rooms, no basements
- UFH thermal response and low cost per m² are the priority
- Engineered wood or LVT is going down over an isolating underlay
- Depths of 50mm+ are needed and drying time isn't critical
Choose cement (Cemfloor) when…
- Any wet room, kitchen or basement is in the pour area
- Tiles, epoxy or polished concrete are the finish
- You need SR1 flatness with minimal cover over UFH
- The programme demands the fastest safe drying window
Calcium Sulphate vs Cement Screed — questions we get asked
Keep reading across the site
Get the chemistry right first time
Tell us what's going in each room and we'll confirm the correct screed chemistry before we quote a single product name.