Screed Moisture: 6 Checks Before Laying Parquet

Six checks must be completed before any parquet is laid: measure screed moisture, verify subfloor flatness and finished level, inspect surface soundness and cleanliness, request the commissioning record for underfloor heating, measure room temperature and relative humidity, and acclimatise the material on site. Skipping them sharply raises the risk of swelling, gapping and squeaking.

Why screed moisture outranks every other criterion

Screed moisture is the single criterion that decides whether installation may start at all. Wood is hygroscopic, which means it constantly exchanges moisture with the air and the substrate around it. If the screed underneath has not finished drying, that moisture migrates upward and creates an imbalance between the HDF core of a laminate board and its decorative top layer. The board responds by cupping, swelling at the edges or lifting along the locking joints.

The widely accepted threshold for cement based screeds is a moisture content below 2 percent by weight. For anhydrite screeds, that is calcium sulphate based systems, the limit is held lower still. Where underfloor heating is present the criteria tighten further, because the moment the system runs, any residual moisture inside the screed is driven rapidly toward the surface.

In practice drying time is directly related to thickness. The general rule of thumb is roughly one week per centimetre for the first 4 centimetres, with a longer allowance beyond that. The calendar alone is never proof. No drying period counts as a guarantee unless it is confirmed by measurement. For more technical reading on the subject you can browse the laminate parquet articles section.

Checks 1 and 2: Moisture measurement and choosing the right method

Screed moisture is determined with an instrument, not by looking at the surface. Two methods dominate on site. The CM test, known as the carbide method, crushes a sample taken from the screed and reacts it with calcium carbide inside a pressure vessel. It is treated as the binding result. Resistance or capacitance based electronic moisture meters are ideal for fast scanning, they are non destructive, but they give a relative indication rather than an absolute value.

The correct approach is to use both together. First the whole area is scanned with the electronic meter, the points returning the highest readings are marked, and then CM measurements are taken at those critical spots. The sample must not come from the surface but from the middle third of the screed thickness, because the top layer is always drier than the body of the slab.

The number of test points matters as well. At least one measurement per independent room is expected, with several repeats across large open areas. Priority locations include the base of external walls, zones next to wet rooms, the perimeter of columns and door openings. Every measurement should be recorded in writing with date, time, location and result, so that the decision to proceed is documented rather than remembered.

Check 3: Flatness, finished level and tolerance

Subfloor flatness must be limited to a deviation of only a few millimetres under a 2 metre straightedge. Common industry practice targets a tolerance of around 3 millimetres over 2 metres. Once that limit is exceeded, the click joints of a laminate floor are no longer loaded evenly. Over time the joints open, and a hollow feeling appears underfoot as you walk across the room.

Flatness is never checked from a single position. The straightedge is moved across the room in different directions, and hollows and humps are marked with chalk. Hollows are filled with a suitable repair mortar or self levelling compound, while humps are ground down mechanically. Minor surface roughness can be sanded away, but structural undulation can only be corrected with a levelling layer.

Finished level is a separate topic. The level at door thresholds, lift entrances, balcony doors and wet room openings has to be calculated in advance according to the chosen build up. Laminate thicknesses between 8 and 14 millimetres need an added allowance for underlay and adhesive. With wide boards such as plank laminate parquet, flatness errors are far more visible, so the tolerance is kept tighter.

Check 4: Surface soundness, cleanliness and vapour barrier

A screed is considered ready when it does not dust, does not flake and does not crumble when scratched. Soundness is tested simply, by scoring the surface with a steel point or a key. If the top layer breaks up like sand, it must be mechanically ground and then primed. Parquet bonded to a weak surface will lift together with that surface no matter how good the adhesive is.

Cleanliness is the second condition. Plaster residue, paint splashes, silicone, lumps of mortar and construction dust must all be removed. An industrial vacuum should be used, and the surface inspected again afterwards. Oil and resin stains interfere directly with adhesive bonding and cannot simply be covered over.

In basements, ground floors and slabs in contact with soil, the vapour barrier must never be omitted. For floating installations a polyethylene sheet of at least 0.2 millimetres is normally laid with overlapped and taped joints. At wall bases the sheet is turned up to skirting height. Where the moisture source is unclear, a test foil taped to the slab can be inspected after 24 hours for condensation underneath.

Step by step screed and subfloor check

Measure temperature and relative humidity in the room and record the values in writing.
Scan the whole floor with an electronic moisture meter and mark the highest reading points.
Carry out CM tests at those marked points to document screed moisture in a binding way.
Check flatness in several directions with a 2 metre straightedge and mark all deviations.
Fill hollows with levelling compound and grind humps down to bring the surface to one level.
Scratch test the surface for soundness, then grind and prime if dusting is present.
Vacuum with an industrial machine and lay the vapour barrier with overlaps where required.
Leave the parquet in its unopened packaging on site for at least 48 hours to acclimatise.

Check 5: Commissioning heated floors

Parquet is never laid on an underfloor heating system that has not been commissioned through a controlled heating cycle. Commissioning drives the residual moisture out of the screed before installation rather than after it. In practice the flow temperature is raised in stages, held at the maximum design temperature for several days, then lowered again in stages. The dates and temperatures of that cycle must be documented by the contractor and handed over.

During normal operation the critical limit is surface temperature. The parquet surface must not exceed 27 degrees Celsius. Above that the wood dries quickly, shrinks along its length and develops open joints. Carpets, thick rugs and furniture with closed bases can trap heat locally, so their positions should be considered at the planning stage rather than discovered later.

Underlay choice is equally decisive for heat transfer. Thick underlays with high thermal resistance reduce system efficiency. Thin underlays declared suitable for underfloor heating, or full bonding, are preferred instead. For readers balancing these factors at home scale, the article on perfect flooring solutions for residential projects offers useful guidance.

Check 6: Ambient conditions and material acclimatisation

At the time of installation the room should be between 18 and 22 degrees Celsius, with relative humidity between 40 and 60 percent. That range is also the climate the floor needs to live in for its whole service life. All wet trades, plaster, paint, render and screed, must be finished and dry beforehand, because parquet is always the last item of work.

Material is left flat on site in unopened packaging for at least 48 hours. That period allows the packs to reach the temperature and humidity balance of the room. Boxes should not lean against walls, sit in front of radiators or be exposed to sunlight under a window.

Expansion allowance is planned at this stage too. A gap of several millimetres is left around walls and fixed elements, and transition profiles are used in large rooms and at doorways. With patterned layouts the preparation is even more demanding. In a Hungarian point laminate parquet installation, a mistake in the centre axis line shifts the entire pattern. She Parquet installation teams run these checks in sequence before work begins. For periodic inspection at seasonal changeovers, the 7 point parquet check before winter is a useful companion guide. She Parquet applies this same technical framework on both the material and the installation side of residential and hotel projects.

Frequently Asked Questions

What should screed moisture be?

For laminate parquet on cement based screeds, a moisture content below 2 percent by weight is the widely accepted threshold. With underfloor heating that limit is pulled lower still. The value should be confirmed by a CM test after electronic scanning.

How long does screed take to dry?

The general approach is roughly one week per centimetre for the first 4 centimetres of a cement based screed, and longer beyond that. Ventilation, temperature and season change the timeline noticeably. The calendar alone is not enough, measurement is mandatory.

What is the flatness tolerance for a subfloor?

Common practice treats a deviation of about 3 millimetres under a 2 metre straightedge as the upper limit. Where it is exceeded, hollows are filled with levelling compound and humps are ground down. With wide plank formats the tolerance is kept tighter.

What surface temperature is allowed with underfloor heating?

The parquet surface temperature should not exceed 27 degrees Celsius. Above that, the risk of excessive drying, open joints and dimensional movement increases. The system must be commissioned with a staged heating cycle before installation.

How long should the material acclimatise before installation?

Packs should rest flat and unopened in the installation room for at least 48 hours. During that time the room should be held at 18 to 22 degrees with 40 to 60 percent relative humidity. Boxes must not be placed in front of heaters or in direct sunlight.