Moisture Control System

Moisture Control System

Moisture Control Systems Concrete is one of today’s most important building materials. Most floor slabs are made of concrete. While concrete itself is permeable to moisture vapor, many modern flooring systems have very low moisture permeability and are susceptible to problems caused by moisture vapor. The moisture control systems manufactured by KÖSTER are designed to be applied on concrete to supress moisture vapor and the problems associated with it.

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Why is moisture vapor an issue?

Flooring failures due to water vapor in concrete floor slabs have been plaguing the construction industry for decades, causing millions of dollars in damage to our economy. Typical damage patterns indicating a serious failure of the flooring system can be blisters in epoxy coatings, bubbles in sheet goods, unsightly staining at seams, adhesive bond failure, loose, curling and cracking VCT, warped wood floors, and damp and mold infested carpets.

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Where does the moisture vapor in floors come from?

Water is present in the ground everywhere, in liquid form as ground water or attached to or between soil particles and in form of water vapor between the soil particles. While slabs on grade are unlikely to come in contact with liquid ground water, they definitely will come into contact with the water vapor that rises through the soil.

If a below slab vapor retarder is missing or defective, water vapor will be able to penetrate the bottom of the slab and accumulate in the slab if it cannot evaporate. Slabs on grade in contact with moist soil can also lead to capillary moisture transfer into the slab. Basement floor slabs may come into contact with liquid water if submerged in ground water.

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How does moisture vapor harm flooring systems?

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Concrete is a porous material. It allows moisture vapor to pass through it. As long as moisture vapor can simply pass though the concrete, there will be a moisture gradient with the concrete drier near the top surface and more damp at the bottom. Moisture can transport salts of various types into and through the concrete causing efflorescence on the surface of the concrete. This can be detrimental to serviceability.

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When a flooring system is installed, it typically has lower vapor permeability than concrete.  The water vapor can no longer evaporate from the surface of the concrete. As a result, the amount of water vapor that is present in the slab will slowly increase. This can be measured as an increase in the relative humidity in the concrete slab. Wood floors can expand and buckle when exposed to high moisture over a longer period of time.

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Once the relative humidity in the surface area of a concrete slab is high, temperatures below the dew point of water at the surface of the slab will cause condensation within the surface layer of the concrete slab. Such temperature regimes can for example be caused by the operation of air conditioning systems.

Now the pores of the concrete below the surface are saturated with water. Cured concrete contains soluble salts of calcium, potassium and sodium. In contact with water, these salts form hydroxides. Once dissolved in water, conditions develop with pH readings up to 14. Adhesives that bond floor coverings to the concrete can degrade and fail as a result of the high pH and moisture present on the concrete. The high pH that develops at the surface of the concrete due to moisture can also discolor floor coverings.

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Once high pH condensed underneath the low permeable floor covering adhered to the surface, the adhesive is directly exposed to the high pH conditions. This is the prerequisite for the formation of liquid filled blisters, which are frequently observed as part of a failure of a flooring system. Such blisters are referred to as “osmotic blisters”. The time frame in which this delamination takes place depends on vapor drive and the composition of the coating as well as that of the concrete. The liquid in blisters can have a pH of 14.


Vapor barrier for priming unsealed interior concrete floors, e.g. against osmotic action under vapor tight flooring. Fields of application: under epoxy, polyurethane or vapor tight flooring e.g. in gymns, industrial halls or sales rooms. KÖSTER VAP I® 2000 is a 2-component, low viscous, solvent-free, transparent special resin.


Technical Information

  • KÖSTER VAP I® 2000 systems withstand a permanently elevated moisture condition up to 100% RH
  • KÖSTER VAP I® 2000 systems resist a sustained exposure to pH 14.
  • KÖSTER VAP I® 2000 systems provide a high degree of user friendliness due to their ease of installation and one coat application.
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