Moisture barrier Underlay
If you have already read up on floor coverings, you have probably also stumbled upon the word moisture barrier. Many manufacturers of floor coverings recommend them or even require them when laying on mineral subfloors. Another word for it is vapour barrier. But what is behind it? The moisture or vapour barrier is a plastic film that insulates the floor covering against the subfloor in such a way that no moisture can rise.
What must be observed during installation?
A moisture barrier is required when laying a floor covering on a mineral subfloor or over a water-bearing underfloor heating system. Mineral subfloors include concrete flooring, cement screed or calcium sulphate screed
These soils contain ever increasing amounts of water. Although this largely dries out, there is always a residue left over. If the floor covering absorbs moisture from these subfloors or from the underfloor heating, joints may form and the floor may expand too much. So the floor is damaged.
The situation is different, however, when the floor is laid on a wooden floor. Wood is a "breathing" material, i.e. it absorbs moisture when the ambient humidity is high. If the ambient air humidity drops, the wood releases moisture. If you would lay a vapour barrier on a wooden floor, this mechanism would be suppressed
As a result, the wooden floor would become unstable and in extreme cases crumble. But this would destroy the foundation of your floor covering. This means that in this case there must be no moisture insulation.
You can buy this moisture insulation from Parquetkaiser either as an individual element in the form of a thin PE film or as a combination product. The combination product combines moisture insulation with footfall sound insulation. This saves you laying work, because one work step is eliminated.
Some technical terms that you will come across again and again
Residual moisture
Freshly laid or poured screed must dry out for several weeks before a floor can be laid on it. This drying time is up to 8 weeks, in individual cases even more. That depends on the environmental conditions
This process can be accelerated by using a dehumidifier. If underfloor heating is present, the heating log must be run through at least once. The moisture still present in the soil after drying is the residual moisture.
It must not exceed the following values for an unheated floor (CM method):
- Elastic floor covering, e.g. vinyl: 2 % for cement screed - 0,5 % for calcium sulphate screed
- Textile vapour-inhibiting floor covering, e.g. carpeting: 2.5 % for cement screed - 0.5 % for calcium sulphate screed
- Textile vapour-permeable floor covering, e.g. carpet: 3.0 % for cement screed - 1.0 % for calcium sulphate screed
- Laminate: 2 % for cement screed - 0,5 % for calcium sulphate screed
- Parquet: 2 % for cement screed - 0,5 % for calcium sulphate screed
For heated screed the values are somewhat stricter (CM method):
- Elastic floor covering, e.g. vinyl: 1.8% for cement screed - 0.3% for calcium sulphate screed
- Textile vapour-inhibiting floor covering, e.g. carpeting: 1.8 % for cement screed - 0.3 % for calcium sulphate screed
- Textile vapour-permeable floor covering, e.g. carpet: 3.0 % for cement screed - 1.0 % for calcium sulphate screed
- Laminate: 1,8 % for cement screed - 0,3 % for calcium sulphate screed
- Parquet: 1.8 % for cement screed - 0.3 % for calcium sulphate screed
Ready for posting:
The term "readiness for covering" indicates that the residual moisture of the screed has decreased to such an extent that a floor covering can be laid.
Screed types:
- CT or ZE = cement screed: the most frequently used screed
- CA = calcium sulphate screed
- MA = Magnesia screed
- Flow screed = screed that is poured.
- Heated screed = screed containing underfloor heating
- CM value = Residual moisture measured value according to the CM method = Calcium carbide measuring device method
There are many more types of screed, but the above are the most commonly used expressions.
How is the CM value measured?
There are several methods for measuring the residual moisture of a screed. They may well provide different values. Therefore, it must always be stated which method was used for the measurement. However, only the CM process is legally binding. Therefore you should use this.
For the measurement a 5 to 6 cm hole is knocked into the screed. Material is now removed from this hole, if possible also from below. It is crushed with a hammer and filled into a steel pressure cylinder. Now add calcium carbide and shake the bottle vigorously. Then let the bottle rest for a few minutes and then shake it vigorously once more. A screwed-on measuring instrument then indicates the moisture content of the material.
This changes if you want to install the vapour control layer over underfloor heating
When laying over underfloor heating, the thermal conductivity must always be taken into account. It indicates how well a material insulates the heat. The bigger it is, the better the isolation. With underfloor heating, however, the heat should be transferred into the room through the flooring material. Therefore this resistance must be as small as possible in this case. Here, the total resistance of the moisture insulation, the footfall sound insulation and the floor covering are added together. This value should be below 0.15 m²K/W. You determine it by adding the individual values.
The most important characteristics of the moisture barrier
- Moisture protection greater than 75 m
- Thermal resistance for products for installation over underfloor heating systems: less than 0.075 m²K/W
- Thermal resistance otherwise: greater than 0,075 m²K/W
- Impact sound reduction for combination products Sound + moisture insulation
- Walking noise reduction for combination products Sound + moisture insulation
- Compensation of unevenness of the floor (mainly for combination products)
- Combination products increase the stability of the connections between the individual floor elements
- durable
- easy to install