Stephen Thornton, flooring and tiling technical manager at Saint-Gobain Weber talks about the importance of preparing your floor properly before tiling to ensure your floor has a long life.
ONE of the most underestimated risk factors when it comes to floor tiling is moisture. While it doesn’t always announce itself on the surface, it can lie undetected and if left unmanaged, it can lead to debonding, adhesive breakdown and, ultimately, full floor failures.
Many know what to test – but not how
A surprising number of installers still rely on surface dryness or visual cues to judge screed moisture. But this can be highly misleading, especially with underfloor heating or fast-drying surface layers. To avoid mistakes, it’s vital to understand the two main test methods.
The CM (carbide bomb) test measures moisture content by weight (CM-%) and requires a representative sample from the body of the screed – not just surface dust. Meanwhile, the RH (relative humidity) method uses in-situ probes to measure the air humidity in the screed and must be properly sealed and equilibrated, often over 72 hours.
Getting this wrong is particularly risky with anhydrite (calcium sulphate) screeds, where residual moisture can trigger ettringite-related failures if cementitious adhesives are applied prematurely.
For anhydrite, CM testing is often preferred, and mechanical laitance removal is non-negotiable before priming or tiling. Training and experience matter and there’s a real opportunity here for the industry to upskill.
Faster drying screeds mean faster project turnaround
Traditional sand and cement screeds can take many weeks – or even months – to dry, particularly when applied thickly or in cool site conditions.
By contrast, Weber’s polymer-modified screeds offer much shorter drying times, often allowing same/next day tiling depending on site conditions and build-up. That significantly reduces project delays, especially when paired with compatible primers and adhesives.
Unlike flowing anhydrite screeds, these systems offer faster moisture release and avoid gypsum-cement compatibility issues.
On sites where speed, certainty and tiling compatibility are essential – such as housing, refurb or fit-out – they provide a high-performance alternative with lower moisture risk.
LECA: lightweight, insulating and moisture-smart
In retrofit scenarios or lightweight construction, LECA (lightweight expanded clay aggregate) can solve multiple problems at once. Used as a free-draining, insulating base layer, LECA offers fast installation without compaction and resists capillary moisture movement. It’s ideal for upgrading floors without adding excessive weight.
Combined with Weber’s pumpable screeds and fast-setting adhesives, this system approach delivers robust moisture management from the ground up. For retrofit and refurb markets facing tighter thermal and damp-proofing requirements, this offers a simple but effective solution.
Tile compatibility: don’t assume, always test
Not all tiles behave the same, especially as resin-backed products and imported materials become more common. Some have extremely low surface energy or backings that resist adhesive bonding – like trying to stick to cling film. Others, such as certain marbles, may be coated with resins that standard adhesives won’t grip to.
The safest approach is to test adhesion with a sample tile before committing to full installation. Always check manufacturer guidance, and when in doubt, carry out a small-scale bond test. A few minutes of due diligence can prevent major failures later.
Ventilation and moisture control matter
Finally, no substrate solution will perform well in a poorly ventilated or improperly heated space. As new homes move towards low-carbon heating and tighter insulation under the upcoming Future Homes Standard, managing internal moisture becomes more challenging.
Condensation, trapped humidity and thermal cycles can all affect screed performance and tile adhesion. Installers should be aware of slab temperature, humidity levels, and ventilation – especially during colder months.
While product guidance often states a minimum of 10deg c, this should be understood as applying to both air and substrate, with consistent temperature and drying conditions across the work period.
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