Testing & handover
Comparing moisture testing methods for liquid screed
An overview comparing the main moisture testing approaches used on liquid screed floors, focused on how they differ rather than a single how-to.
Several methods exist for assessing whether a screed is dry enough for floor coverings, and they don't all measure the same thing or offer the same reliability — a quick surface reading and an in-situ probe test can give very different pictures of the same floor.
Choosing the right method — and understanding what it actually tells you — matters more than simply picking whichever is quickest, since a flooring failure caused by residual moisture is far more costly to put right than the time saved by skipping a proper test.
This page sets out how the main methods differ, so a sensible choice can be made based on the flooring being installed and how much confidence is needed in the result, rather than defaulting to whichever test happens to be to hand.
Moisture testing methods compared — the points that decide it
- 1Surface hygrometer readings are quick but only assess conditions at the surface, not moisture content through the depth of the screed.
- 2Relative humidity (in-situ probe) testing measures conditions within the depth of the screed and is widely regarded as a more reliable method for flooring decisions.
- 3Carbide bomb (calcium carbide) testing gives a direct moisture content reading from a sample but is destructive and less commonly used for calcium sulfate screeds.
- 4Manufacturer-specific guidance for the flooring adhesive or covering being used should always be checked, as acceptable moisture thresholds vary by product.
- 5Testing location and number of test points matters, since moisture content can vary across a floor, particularly near external walls or over UFH pipework.
- 6Results should be interpreted alongside drying conditions and elapsed time, not read as a single pass/fail number in isolation.
- 7Test equipment needs to be calibrated and used correctly, since a poorly conducted test can give misleading results regardless of the method chosen.
- 8The stage at which a screed is tested relative to any heating being run matters, since heating can affect readings if not paused correctly beforehand.
- 9Repeat testing may be needed if initial results are close to the required threshold, rather than proceeding on a borderline reading.
Why surface readings alone can be misleading
A screed can feel and read dry at the surface while retaining significant moisture deeper in the section, particularly at greater depths. This is why in-situ probe testing, which assesses conditions within the depth of the material, is generally preferred ahead of sensitive floor coverings.
Surface readings still have a role as an early, low-cost indicator during the drying period, giving a rough sense of progress before committing to a more formal in-situ test closer to the intended covering date.
Matching the test to the flooring being installed
Different floor coverings and adhesives have different moisture tolerance, so the acceptable threshold for one covering may not apply to another. The appropriate test and threshold should be confirmed against the specific flooring manufacturer's requirements.
Resilient coverings such as LVT and certain adhesive systems can be particularly sensitive to residual moisture, so it is worth checking requirements before assuming a threshold that may have applied to a previous, different flooring type.
Preparing the floor correctly before testing
In-situ probe testing typically requires drilling into the screed to the correct depth and allowing conditions to stabilise before taking a reading, so testing too soon after drilling, or in a draught, can distort results.
Where underfloor heating is present, guidance usually calls for the heating to be switched off for a period before testing, since running heating can artificially lower a surface reading without the underlying moisture content having actually changed.
Interpreting borderline or inconsistent results
A single reading close to the threshold, or results that vary noticeably between different points on the same floor, are usually worth investigating further rather than accepted as a pass on the strength of one favourable test point.
Where results vary across the floor, this can point to uneven drying conditions — perhaps near an external wall, over pipework, or in a poorly ventilated corner — which may need addressing before retesting rather than simply averaging the readings.
Unsure which moisture test suits your project?
Talk to us about your flooring choice and we can advise on an appropriate testing approach.
Or call our landline on 01392 237700
Moisture testing methods compared — your questions
In short
An overview comparing the main moisture testing approaches used on liquid screed floors, focused on how they differ rather than a single how-to.
Other pages that answer this properly
Unsure which moisture test suits your project?
Talk to us about your flooring choice and we can advise on an appropriate testing approach.