Damp-proof membrane risk
DPM Failure Under a Screed Floor
A liquid screed is only as dry as the ground beneath it lets it be. When the damp-proof membrane fails, moisture rises straight through, no matter how well the pour went.
Suspect a DPM problem under your screed?
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The damp-proof membrane (DPM) sits between the ground slab and the screed above, stopping ground moisture from migrating upward. It's usually invisible once the screed is down, which means a failure in it — a puncture, an unsealed lap, or a membrane that was never continuous in the first place — often isn't discovered until a moisture problem appears months later.
Because the screed itself did nothing wrong, DPM failure is a frustrating diagnosis: the pour, the mix and the finish can all be perfect, and the floor still won't pass a moisture test or the flooring above still delaminates, because the water is coming from below, not from the screed drying process.
This page covers how we tell the difference between a slow-drying screed and a genuine DPM failure, and what the remediation actually involves.
Signs pointing to a DPM issue rather than a drying issue
- Moisture readings that plateau or rise again after an extended drying period
- Damp patches that reappear in the same location after being dried out
- Musty smell persisting well beyond the expected drying window
- Flooring failures concentrated near known slab penetrations or perimeter edges
- A history of known groundwater or high water table on the site
How we investigate a suspected DPM failure
- 1
Extended moisture testing
Hygrometer or carbide readings taken over time rather than once, to see whether moisture is falling normally or plateauing.
- 2
Localise the pattern
Mapping affected areas against known service penetrations, edges and joints often points straight to where a membrane lap or puncture would be.
- 3
Core inspection
A core sample can sometimes reveal a visible membrane defect directly beneath the screed.
- 4
Confirm the source
Where needed, we bring in specialist damp surveying to confirm ground moisture ingress rather than assuming it.
DPM failure vs slow screed drying
| Indicator | Likely cause |
|---|---|
| Moisture falling steadily but slowly | Normal drying — needs more time or ventilation |
| Moisture plateaued or rising | Possible DPM or ground moisture ingress |
| Localised damp near penetrations | Membrane puncture or unsealed lap |
| Uniform dampness across whole floor | Membrane never continuous, or absent |
Suspect a DPM problem under your screed?
Get an extended moisture assessment before assuming it just needs more time. We'll tell you plainly what the readings show.
Waiting longer won't dry out a genuine DPM failure — it will just delay finding it. Extended moisture monitoring is the only reliable way to tell the two apart.
— Exeter Liquid Screeders
DPM Failure Under Screed — questions we get asked
Keep reading across the site
Suspect a DPM problem under your screed?
Get an extended moisture assessment before assuming it just needs more time. We'll tell you plainly what the readings show.