SUPPLY & FIT · DUNFERMLINE & FIFE

SUBFLOORS & PREPARATION

How we actually test a floor for moisture before fitting

"It should be dry by now" isn't a test, it's a guess, and we've seen enough guesses go wrong to insist on an actual reading before certain floors go down. Here's what that testing actually involves.

WHAT IT IS
A measurement of residual moisture in a subfloor, using electronic meters and, where results are borderline, more thorough hygrometer methods.
TEST WE RUN
Surface moisture meter as a first check, escalating to an in-situ hygrometer or calcium carbide test for higher-stakes finishes.
TOLERANCE
Different floor finishes and adhesives have their own moisture limits, commonly quoted in manufacturer datasheets rather than a single universal figure.
FAILURE MODE
Relying on drying time estimates alone rather than an actual measured reading before covering the floor.

The methods we use, in order of thoroughness

  • Electronic moisture meter for a quick, non-invasive first indication across the room.
  • In-situ hygrometer testing where a probe measures relative humidity within the slab itself, generally considered a more reliable method for higher-risk installations.
  • Calcium carbide testing in specific cases, which gives a direct moisture content reading from a sample.

Why we test rather than estimate by time

Drying time depends on slab thickness, ventilation, weather during the build and whether a membrane is present, so two identical-looking rooms can dry at very different rates. We've been called to properties where a floor was assumed dry based on how long ago it was poured, only for a reading to show it was still well above what the chosen finish could tolerate.

What happens if we get a high reading

We won't fit a moisture-sensitive finish over a floor that tests wet. Depending on the reading and the job, options include waiting longer for the floor to dry naturally, improving ventilation, applying a suitable damp-proof membrane, or choosing a floor finish that's less sensitive to residual moisture.

Finishes with different tolerances

Solid hardwood and some laminate products have the least tolerance for residual moisture, adhesive-based LVT and carpet sit in the middle depending on the specific product, and certain rigid-core and fully waterproof products are generally more forgiving, though manufacturer guidance should always be the final word rather than a general rule.

Fife reality: new builds and coastal humidity

New-build slabs across Glenrothes and Duloch often need testing regardless of how recently they were poured, given how much drying time varies. In coastal areas like Aberdour and Burntisland (KY3), general ambient humidity can also be higher, which is worth factoring in alongside the slab reading itself when choosing a finish.

Questions we get asked

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