RH & moisture testing
Failed a Screed Moisture Test — What Happens Now
A relative humidity reading above the threshold for your chosen floor covering is a common, manageable outcome — it means the floor needs more time or more help drying, not that anything has gone wrong with the screed itself.
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Every floor covering has a moisture threshold it needs the substrate to be under before it can go down safely — typically 75% relative humidity for most adhesives and coverings, tighter again for some resin and wood finishes.
A test that comes back above that figure simply means the screed hasn't finished releasing moisture yet. It happens more often than people expect, usually because ambient conditions on site have been colder, damper or less ventilated than assumed.
This page explains how the test actually works, what a failed result really means, and the practical steps to get from a failed reading to a signed-off pass.
How we test screed moisture
- Hygrometer boxes sealed to the surface for a minimum dwell time, reading relative humidity in the pocket of air beneath
- Calcium carbide (Speedy) testing where a faster, destructive sample reading is needed
- Multiple test points across the floor, not a single reading, since moisture can vary room to room
- Testing at the depth relevant to the pour thickness and covering being installed
Typical RH thresholds by covering
| Floor covering | Maximum RH before laying |
|---|---|
| Ceramic/porcelain tile (cement adhesive) | Up to ~90–95% acceptable with the right adhesive |
| LVT / vinyl | ≤75% RH typical requirement |
| Engineered wood | ≤65–75% RH depending on manufacturer |
| Resin/epoxy coatings | ≤75% RH, often tighter |
From a failed test to a pass
- 1
Confirm the actual result
We re-check the test method and dwell time before assuming the reading itself is right.
- 2
Improve conditions
Ventilation, heating and airflow adjustments to encourage natural drying.
- 3
Dehumidify if the programme is tight
Forced dehumidification can bring a stubborn reading down meaningfully faster.
- 4
Retest and certify
We retest and provide a written result once the floor is genuinely ready.
Get a moisture test done properly
Whether it's a first test or a retest after a failed reading, we'll test at the right points and give you a clear written result.
Signing off a moisture test that hasn't genuinely passed just moves the failure downstream to the flooring trade — we'd rather hold the date and get the number right.
— Exeter Liquid Screeders
Failed Moisture Test — questions we get asked
Keep reading across the site
Get a moisture test done properly
Whether it's a first test or a retest after a failed reading, we'll test at the right points and give you a clear written result.