Prep and adhesive compatibility compared
Tiling Over Anhydrite Screed vs Cemfloor
Tiling directly onto the wrong screed chemistry without the right prep is one of the most common — and most avoidable — flooring failures we see.
Planning tile over an existing screed?
Name, phone, email — we'll reply the same working day with a fixed price.
If tile is the final finish, the chemistry of the screed underneath changes everything about the prep required. Anhydrite (calcium-sulphate) screeds need laitance sanding and a primer compatible with gypsum chemistry before tiling. Cemfloor, being cement-based, is far more tile-friendly out of the box.
This isn't a minor technical footnote — using the wrong adhesive or skipping prep on an anhydrite screed is a leading cause of tile debonding and cracking in wet areas.
This page sets out exactly what's needed for each, so whoever's tiling your floor — us, your own contractor, or a specialist tiler — knows what they're dealing with.
Tiling prep compared
| Step | Anhydrite vs Cemfloor |
|---|---|
| Laitance removal | Mandatory sanding before any adhesive vs generally not required |
| Primer | Gypsum-compatible primer essential vs standard primer per datasheet |
| Adhesive type | Must be moisture-tolerant, gypsum-rated adhesive vs standard cement-based tile adhesive usually fine |
| Moisture testing | Critical — anhydrite is moisture-sensitive long term vs still required but less critical to long-term durability |
| Wet room suitability | Needs careful detailing and isn't our first choice vs naturally well suited |
Correct sequence for tiling over anhydrite
- 1
Moisture test
Confirm the screed has reached the manufacturer's target RH before any further work.
- 2
Sand laitance
Mechanically sand the surface to remove the weak laitance layer.
- 3
Prime
Apply a gypsum-compatible primer across the full area.
- 4
Tile with correct adhesive
Use a flexible, moisture-tolerant adhesive rated for anhydrite substrates.
Planning tile over an existing screed?
Tell us which screed is specified and we'll confirm the correct prep sequence, or spec Cemfloor from the outset to simplify it.
If tile is the confirmed final finish and it's our choice of screed, we'll spec Cemfloor every time — it removes several steps of risk. Where anhydrite is already specified elsewhere in the build, we follow the sanding and priming sequence to the letter, no shortcuts.
— Exeter Liquid Screeders
Tiling Over Anhydrite vs Cemfloor — questions we get asked
Keep reading across the site
Planning tile over an existing screed?
Tell us which screed is specified and we'll confirm the correct prep sequence, or spec Cemfloor from the outset to simplify it.