Can cause moisture to rise through concrete


Residual moisture in mineral substrates can only be blocked off if the residual moisture remaining in the substrate does not damage the substrate. Usually this works very well on cement screeds. Gypsum-based screeds (calcium sulfate / anhydrite) and magnesia screeds, on the other hand, can be decomposed by moisture and their structure weakened.
With today's fast construction method, what is the possibility of laying floor coverings / floor coverings promptly, if necessary despite increased residual moisture in the subsurface?

In principle there are three different systems for blocking moisture from the subsurface. A distinction must be made between floating floor coverings and fully bonded floor coverings; epoxy resin and polyurethane-based systems have proven themselves on the market for years.

  1. In the case of floating floor coverings (e.g. laminate floors, prefabricated parquet floors, cork parquet, etc.), there is the option of installing a vapor barrier or vapor barrier in addition to the footfall sound-insulating underlays. The systems known here are 0.2 mm PE films with a vapor-retarding effect, but also stronger PVC films with a vapor-barrier effect.

  2. A simple and inexpensive alternative in terms of laying technology are footfall sound insulation underlays, which have already been provided with a laminated aluminum foil by the manufacturer.

  3. If floor coverings / floor coverings are laid fully glued, the films or underlays mentioned under 2 cannot be used. In this case, it is possible to block off the mineral substrate against residual moisture / rising moisture. Mainly two systems are offered here: 2-component epoxy resin primer systems, which are applied in 2 layers crosswise at 90 °. These 2-component primers form a dense film on the surface of the substrate, which has a firm hold to the substrate and a sufficient vapor-retarding effect. Or, as an alternative, a 1-component polyurethane primer, which is set to have a significantly lower viscosity and thus has the option of penetrating even deeper into the pores / capillaries of the screed construction. Since moisture escapes from the subsurface in the mineral screed construction via capillaries, a vapor barrier effect can be achieved by filling this capillary. For both systems, the manufacturer's permissible limit values ​​must be observed.

If mineral substrates on the surface are sealed against residual moisture, it must be ensured that the moisture can escape via the wall / edge joints. Either ventilated skirting board systems or moisture-resistant materials are to be used here.

Caution is also advised with regard to heated screed constructions. By operating underfloor heating, the moisture remaining in the screed is "forcibly" pushed upwards. Barriers can therefore only be used on underfloor heating if they have been explicitly approved by the manufacturer for this area of ​​application. Here, too, the residual moisture content and the type of underfloor heating (flow temperature, maximum surface temperature, etc.) must be observed.

Source: Institute for Floor Construction, Torsten Grotjohann,Overath

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