Screed drying before tiling or parquet flooring: deadlines by type and thickness, residual moisture thresholds, carbide bomb test, and mistakes to avoid in Belgium.
The screed has just been laid. The tiler calls back to set a date. The parquet company is waiting for the green light. And you, you're wondering: is it ready or not yet?
This is the question we're asked most often on site. The honest answer: it depends. And getting it wrong can be very costly. Here's everything you need to know to avoid making a mistake.
We commonly refer to screed "drying," but this term is technically inaccurate. What happens in the first few weeks after laying is primarily a chemical hydration reaction : cement (or anhydrite) reacts with water to form crystals that harden the material. It's not simply evaporation.
This nuance explains why the surface may seem dry and hard a few days after laying, while the interior is still laden with moisture. And that's precisely where mistakes happen: you see a "dry" surface, you lay the covering, and the mess appears weeks later.
Walkable doesn't mean ready for covering. These are two very different states.
The basic rule: approximately 1 week per centimeter of thickness up to 5 cm, then 2 weeks per additional centimeter beyond that. These timelines apply under optimal conditions: 20 °C ambient temperature and relative humidity below 65%.
The screed is walkable after 24 to 48 hours, but that says nothing about its readiness to receive a covering.
It's a little-known paradox: anhydrite screed is quick to lay and self-levels, but it retains moisture for longer than cement screed and imposes much stricter residual moisture thresholds. It is walkable after 48 to 96 hours (4 days), but the waiting period before laying the floor covering is comparable, or even slightly longer, than for cement screed.
Critical point: anhydrite is sensitive to water. Prolonged exposure to moisture during the drying phase can irreversibly degrade it.
For projects with tight schedules, accelerated drying screeds offer significant gains. The saving can be up to 27 days off the construction schedule compared to a traditional screed. When deadlines are tight, this is an option to consider from the outset.
Each of these errors can cause delamination, blistering, or cracking of the flooring, or even void the installer's warranty if the screed did not meet the required thresholds at the time of installation.
This is the only legally recognized method in Belgian construction. How it works:
The thresholds to be met before any glued installation:
This document is the only valid one in case of a dispute with the flooring installer. Request it before giving the green light for installation.
Place a 50 x 50 cm plastic film on the screed and secure the edges with tape. Leave it for 24 hours. If condensation appears under the film: the screed is still too damp. This test is useful as a first indicator before calling the tiler, but it has no legal value.
Some moisture-regulating adhesives allow installation on cement screed as early as 1 week in certain cases. However, residual moisture thresholds still apply: check with your tiler for products suitable for your situation.
Wood is hygroscopic: it absorbs residual moisture and deforms irreparably. Parquet laid on a still-damp screed will swell, open its joints, and lift. For glued solid parquet, a 2% threshold on cement screed is imperative. Engineered wood flooring installed as a floating floor is slightly more flexible, but the risk remains real. The parquet must also be acclimatized in the room for 7 days before installation.
Less sensitive to moisture variations than wood, but the adhesive reacts to residual moisture in glued installations. The thresholds apply with the same strictness. For floating installations, the margin is slightly more flexible, but staying below 2% remains the cautious benchmark to avoid any long-term issues.
For glued installations, residual moisture thresholds are imperative: the adhesive reacts directly to the screed's moisture and can decompose or form bubbles. For floating installations, the requirement is theoretically a bit more flexible, but the 2% threshold remains the cautious benchmark. The risk of long-term issues is merely postponed, not eliminated.
To learn more, check out our articles on the traditional screed vs anhydrite liquid screed, on the mistakes to avoid before pouring a screed and on screed and underfloor heating.
Davide Chape tells you exactly when your floor is ready to receive its covering. We perform carbide moisture measurements on-site and provide you with a certificate. Contact us for a quote or a measurement.
Do not hesitate to contact us directly: our team is always available to assist you and provide a 100% free quote.
Your expert in screeds, thermal insulation, and acoustic floor insulation.
