Drying screed for hardwood floors – how long?

An even, firm and dry screed is an absolute requirement for the professional laying of parquet and a durable, high-quality floor. In this article you will learn what is important for the professional installation of the subfloor and how long screed for parquet must dry.

Testing of the subsoil

In principle, it is possible to lay parquet on various floors (also existing floor coverings such as PVC, felt or stone) provided they are flat, firm and dry.

The corresponding requirements for the substrate are precisely defined in DIN 18365 for floor covering work and DIN 18356 for parquet work.

If parquet is laid by a specialist, it is subject to a test obligation in accordance with these standards.

Should parquet be inserted on a newly built screed important aspects need to be taken into account in order to meet the conditions for a successful installation.

Flatness

Only a flat surface ensures an optimal result when laying the parquet floor.

Therefore, the flatness of the screed should be checked. This works best with a straight object, such as a straightening bar, a measuring wedge, or a water scale.

If the subfloor does not comply with the standard, the screed must be repaired accordingly before laying parquet.

Strength

In order for the underbody to achieve the necessary level of load-bearing capacity, it must have the appropriate strength.

In particular for the full-surface bonding of parquet using parquet adhesive, a solid screed is the decisive criterion for proper installation.

The condition of the substrate is checked by means of a lattice-scratch test.

For this purpose, diamond-shaped lines are carved into the screed with a pointed object or a special scratching device. There must be no eruptions or seds, otherwise it is not firm enough.

Drying time of the screed

Too much moisture in the subfloor is quite likely to cause damage to the floor covering sooner or later – regardless of whether it is hardwood flooring, vinyl flooring- or cork flooring.

If a new floor is not laid sufficiently dry, it can lead to increased swelling behavior, especially for wooden floors or coverings with support material made of wood fibreboards.

Unattractive dents and bulges, especially in the impact areas, are the result.

Caution is also required with barrier primers, as although moisture penetrates more slowly, it still remains in the house.

Receipt maturity of the screed

Careful procedure, sufficient drying time and exact residual moisture measurement are therefore basic requirements for the readiness of the screed for laying – only then is the subfloor suitable for laying parquet.

Screed is available in various versions, which are reflected in their composition and their drying time. Among the most common species Count:

Cement screed

The most commonly used cement screed consists of sand, cement (as binder) and water – and is therefore one of the flow screeds.

Supplied as a dry mixture, flow screed is mixed directly on site with the addition of water and introduced via a screed pump.

Cement screed is suitable for both indoor and outdoor use due to its moisture resistance and has stable strength values.

During installation and during the drying phase, the ambient temperature must not be below 5°C, draughts and humidity must be avoided – otherwise the surface may become uneven or even cracked.

When is cement screed accessible?

After 2 to 3 days the cement screed can be walked on, after approx. 10 days it can be fully loaded, the readiness for laying is reached after approx. 4 weeks drying phase.

Anhydrite screed

The anhydrite screed, which is also one of the flow screeds, is also enjoying increasing popularity, as the contained binder anhydrite shortens the drying phase.

Due to its good thermal conductivity, anhydrite screed is ideally suited for underfloor heating systems, but on the other hand it is not suitable for outdoor use, as the screed becomes unusable on contact with water.

Dry screed

There is no drying time when dry screed is used. Prefabricated panels made of plasterboard, wood-based material or cement-bound chipboard glued or screwed on the raw floor. Unevenness or too low construction heights must be balanced with granules or be piled up.

In addition, there are other, less common screed screeds such as magnesite screed, cast asphalt screed or synthetic resin screed.

Residual moisture determination

When drying ledges, approximately 1 cm of screed per week is generally considered to be a guideline.

If the screed is over 4 cm thick, two additional weeks should be taken into account, as it has an extended binding time.

In the case of underfloor heating, it is also recommended to heat the screed completely afterwards.

For this purpose, the flow temperature of the underfloor heating system is increased to two thirds of the heating load in 5°C increments and then lowered again. A detailed heating protocol should be kept for control.

After the drying or heating phase, an exact test of the residual moisture is necessary.

Measuring points that have already been set when the screed is applied facilitate the process and ensure a reliable result. Fast binders can affect the values and should therefore be disclosed.

The permissible residual moisture depends on both the type of as well as whether or not underfloor heating is available. Depending on the screed, the standard values are as follows:

• cement screed: 2 % without floor heating / 1.8 % with floor heating
• anhydrite screed: 0.5 % without underfloor heating / 0.3 % with underfloor heating
• magnesite line: max. 4 %

Some parquet adhesives are already approved for higher residual moisture. However, the manufacturer’s information should always be treated with caution.

Moisture measurement with CM method

For residual moisture determination, the measurement is recommended using the CM method (calcium carbide method).

For this purpose, the pressure pressure of a crushed and shaken with calcium carbide is measured with a special device and determined as a value for the residual moisture using a conversion table.

Since the measurement is in principle very complex – and also the only approved test procedure for the publisher’s stiffener – it is recommended to contact a specialist.