Checking and preparation of the subfloor

The preparation of the subfloor, which is particularly important for glued flooring, requires that the subfloor be flat, clean, sound, dry and solid.

  • Flat: According to the DTU 21 concerning "Screeds and slabs based on hydraulic binders", the maximum acceptable deviation for a concrete screed is 7 mm for every 2 meters. Failure to observe this maximum deviation should lead to the refusal of the surface by the parquet layer (due to the risks of splitting).
  • Clean: The parquet layer should scrape away all traces of paint, plaster, laitance. They should also thoroughly clean the area with an industrial-strength vacuum cleaner. (Watch out for splatters of greasy materials and plaster).
  • Sound: This refers to water vapour that can affect the subfloor, especially in the case of installation on the ground floor or over empty underfloor spaces which require special care - (one needs to put a waterproof barrier into place).
  • Dry: The moisture content of subfloor must be checked by the before installing the flooring through the use of an adapted system: it must be less than 3%.
  • Solid: You should check the cohesiveness of the surface The subfloor should be free of dust. Superficial scraping should not raise dust, nor indent or chip the subfloor.


In the case of a glued down flooring, the absorption of the subfloor must be checked; to do this, the person installing the flooring can carry out the "water drop" test: a drop of water placed on the subfloor should disappear after about 1 minute when its absorptive characteristics are normal (more rapidly if the subfloor is too porous, more slowly if the subfloor is too impermeable).