Who this guide is for
- Owners whose floor covering has been programmed against a build date
- Self-builders about to lay a covering over a new screed or topping
- Anyone who has had a covering lift, cup or discolour some months after laying
- Project managers reconciling a screed pour with a covering installation
- Anyone being asked to accept a base as ready to receive a floor
Two different meanings of dry
A wet layer becomes walkable long before it becomes ready. The entries separate the two directly: a topping is assumed to be dry when it is walkable, when drying to a state that will accept an impermeable finish takes far longer. Walkable is a construction milestone. Ready is a property measured against what is about to be laid.
Wet toppings introduce a large amount of water into a building and take time to give it up, and laying impermeable finishes too early is described in the library as a recognised cause of failure.
Readiness is judged by testing, not by appearance
The ground-bearing slab entry says it plainly among its misunderstandings: a flat-looking slab is taken for a base ready to receive a covering, when readiness is judged by testing rather than by eye. Whether a covering can be laid, and when, is judged by testing and by the covering manufacturer's documentation rather than by appearance.
That is why the question that matters is procedural rather than technical. Who is carrying out the testing, against what, and what happens if the result is not what the programme assumed.
What the layers below decide about drying
Drying is not a property of the screed alone. A floating build-up can generally only dry upward, so what sits below sets how long the layer takes and what may be laid over it. A screed laid over a barrier cannot dry downwards at all, which is why the barrier arrangement beneath decides how the screed can dry.
The answer therefore depends on the layers below as much as on the screed, and a period quoted for a screed in isolation is answering a different question from the one being asked.
Three separate moisture problems meeting in one floor
In a ground floor, rising moisture, construction water held in the slab and moisture trapped under an impermeable covering are separate problems meeting in the same place. They have different sources and different remedies, and a covering laid too early can convert the second into the third.
This is one reason a covering failure resists simple attribution. The visible symptom sits at the top of a stack whose behaviour was settled several layers down and several months earlier.
What a failure looks like later
The entries do not describe symptoms in detail, and this guide will not invent them. What they do establish is the shape of the problem: the failure is delayed, it appears in the covering rather than in the base that caused it, and it is a recognised consequence of laying an impermeable finish over a layer that had not given up its water.
That delay is what makes the decision worth taking seriously at the time. By the point the covering shows it, the base is buried and the programme pressure that produced the decision is long forgotten.
Why this ends up as a documentation dispute
Slab flatness, moisture condition and the barrier arrangement all have to be recorded, because later trades take decisions from them. The entries put it memorably: a floor covering dispute is usually a documentation dispute about what the base was when it was handed over.
So the record is not administration after the fact. It is the thing that makes the handover of a base from one trade to another a defined event rather than an assumption.
- What the base was measured to be, and when
- Who carried out the measurement, and against what requirement
- What the covering manufacturer's documentation asked for
- What the barrier arrangement beneath the layer is, and which way it can dry
The question to ask before the programme is fixed
What has to be measured before the floor covering can be laid, and by whom. Asked while the programme is still being written, it changes the sequence. Asked on the day the covering is due, it is a request to stop work that somebody has already paid for.
Before a covering is laid on a new base
- 1Ask what has to be measured before the covering can be laid, and by whom.
- 2Obtain the covering manufacturer's documentation and read what it asks of the base.
- 3Establish which way the layer can dry, and what sits beneath it.
- 4Ask whether a barrier below prevents downward drying.
- 5Ask whether the programme allowed for drying or assumed a date.
- 6Establish who owns the decision to proceed if the result is not what was assumed.
- 7Ask for the flatness and moisture condition of the base to be recorded at handover.
- 8Ask what the barrier arrangement beneath is, and have it recorded with the rest.
- 9Confirm whether anything is embedded in the layer that affects how it dries.
- 10Agree who is present when the base is handed from one trade to the next.
- 11Keep the testing record with the covering documentation as one file.
- 12If a covering is laid early against advice, record that decision and who took it.
Common mistakes to avoid
- Estimating drying from the programme rather than testing the base about to receive the covering.
- Treating a walkable layer as a dry one, when drying to accept an impermeable finish takes far longer.
- Judging readiness by how flat and clean the base looks.
- Quoting a period for a screed without accounting for what sits beneath it.
- Laying an impermeable covering over a layer still giving up its water.
- Handing a base from one trade to another without recording what it was.
- Discovering the question on the day the covering is due, when it had to change the programme.
When to involve a professional
- What a base has to be like before a particular covering is laid is set by that covering manufacturer's documentation.
- Moisture testing of a floor base is carried out by competent people against a defined requirement, and nothing here states a method or a value.
- Nothing here states a drying period, and none can be inferred from any part of this guide.
- Diagnosing a covering failure in an existing floor requires investigation of the whole build-up rather than inspection of the surface.
Frequently asked questions
Questions readers ask about this topic
How long does a screed take to dry?
No period is stated in the reference entries and none is stated here, because the answer depends on the layers below as much as on the screed itself. What a covering needs is judged by testing the base rather than by a figure applied to the material.
The screed is walkable — can the floor go down?
Walkable and ready are different states. The entries note that a topping is assumed dry when it is walkable, and that drying to a state which will accept an impermeable finish takes far longer. Readiness is measured against what is about to be laid.
Why does the layer underneath change the drying?
Because a floating build-up can generally only dry upward, and a screed laid over a barrier cannot dry downwards at all. What sits below therefore sets how long the layer takes and what may be laid over it once it is done.
Who is supposed to test the base?
The entries put the question to professionals rather than naming a trade: what has to be measured before the floor covering can be laid, and by whom. Settling that before the programme is written is what turns a handover into a defined event.
Why do covering failures become arguments about paperwork?
Because the base is buried by the time the covering shows anything. The entries describe a floor covering dispute as usually a documentation dispute about what the base was when it was handed over, which is why the record is made at the handover rather than afterwards.
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