Screed moisture testing
Moisture Testing Floors Before Floor Coverings
A screed can look dry and still hold enough moisture to ruin tiles, timber or vinyl. We test the floors we pour and give you the reading in writing before coverings go down.
Need a screed signed off for coverings?
Name, phone, email — we'll reply the same working day with a fixed price.
Or call our landline on 01392 237700
Moisture testing floors is the step between a screed that is walkable and a screed that is ready for coverings. Liquid screed takes foot traffic after 24–48 hours, but drying takes weeks, and most flooring failures we hear about come from coverings laid too soon.
On the screeds we pour, we take moisture readings before handover and give you a written record with the result and the conditions on the day. On larger sites and new-build developments we do this plot by plot, so each unit has its own record rather than one blanket certificate for the site.
This page explains what a screed moisture test involves, what the numbers mean, and how the record helps your flooring contractor. For the technical comparison of test methods, see moisture testing methods compared.
How a screed moisture test runs
- 1
Check the conditions
We note the room temperature, humidity and ventilation, because these affect both drying and the reading.
- 2
Choose the test points
Readings are taken across the floor, including slower-drying spots such as deeper areas, corners and away from windows.
- 3
Take the readings
A CM (carbide) test measures the moisture content of a sample of the screed; a hygrometer measures the relative humidity of air sealed against the floor.
- 4
Compare with the covering
The result is checked against the limit the flooring manufacturer or specification asks for.
- 5
Write it down
You get a written record with the readings, locations and ambient conditions, ready for the flooring contractor or your QA file.
What the readings are compared against
| Situation | What usually governs the limit |
|---|---|
| Tiles on liquid screed | Commonly below 0.5% by CM test, or the tile adhesive maker's limit |
| Cement-based screed before coverings | A relative humidity reading, often 75% RH or below |
| Resilient floors (vinyl, LVT) | The flooring maker's instructions and standards such as BS 8203 |
| Engineered or solid timber | The timber supplier's stated limit, often stricter than for tile |
Why a written moisture record matters
- The flooring contractor takes over the floor knowing the reading, so there is no argument later about whose fault a failure was.
- On developments, each plot has its own record for the site file or building inspector.
- It shows when underfloor heating has been commissioned and the floor dried properly, not just walked on.
- If a reading is too high, you know before the coverings are bought and laid, not after.
When a floor is not dry enough yet
A high reading is not a fault in itself; it means the floor needs more time or better conditions. Ventilation and steady background warmth help. Forcing the drying with unvented heaters can cause curling and cracking, so we advise against it. With underfloor heating, the first heat cycle can be used once the manufacturer's point is reached; our underfloor heating screed guide covers the timings.
Anhydrite screeds also need the surface laitance sanding before bonded coverings, which helps the floor breathe as well as giving the adhesive a sound surface. Our anhydrite screed page explains that step.
If your screed was laid by someone else and you are unsure whether it is ready, call us on 07791 510849 to talk it through. For the pass and fail thresholds in detail, see moisture testing methods and criteria.
Frequently asked
Need a screed signed off for coverings?
Send your name, phone and email with the floor area and the covering planned. We reply the same working day.