The screed is an approx. five centimeter thick leveling layer that is applied directly or indirectly to the unfinished floor. Gypsum or cement are available to the user as a building material. Both types of screed have their advantages and disadvantages. Read everything you need to know about the individual screed types in this text.
What does a screed have to do?
The main task of a screed is to level an uneven floor. Therefore, every screed is a very fine-grained raw mass, which hardens to form a solid surface. Screed is easy to work with. It can be installed with simple tools and almost always succeeds.
If you really just want to get a rough and bumpy concrete floor nice and smooth, a simple cement-sand mortar will suffice. This is ideal, for example, as a base in a garage. The floor is nice and smooth and can be kept clean or further coated as desired. However, this type of screed applied directly to the raw concrete is unsuitable for residential buildings.
Soundproofing through floating screed
A special form of screed has become established in residential buildings and, above all, in apartment buildings. This type of screed does not differ in the material, but in the structure of the simple garage screed: The so-called floating screed is not applied directly to the concrete. A thin layer of insulation is installed between the screed layer and the concrete floor. This layer usually consists of Styrofoam or Styrodur. However, alternative fiber-based materials are also available.
Tip: Use as little polystyrene as possible in your house or do without it altogether. Disposal costs have exploded in recent months. You thus prevent a massive loss in value of your house if you stop using polystyrene.
The insulation layer between the screed and the concrete floor means that the impact noise is interrupted. Without impact sound insulation, every noise on the floor is transmitted throughout the house. This can be extremely annoying, especially for tenants living below. Floating screed is simply part of the standard these days. It is very easy to implement. Its processing requires a lot of care. The screed must not touch the floor or walls directly at any point. Installed with a little expertise and conscientiousness, the floating screed is hardly more expensive than a simple leveling layer.
Warm feet from the underfloor heating
Underfloor heating is a wonderful comfort feature that significantly increases the feel-good climate in a house. Today’s systems are fairly inexpensive and easy to install. In this context, it is important to know that both anhydrite screed and cement screed are suitable for installation on underfloor heating. In both cases, however, the raw screed compound must be mixed extremely thinly so that it really completely encloses the hoses. Flowable screed always means a high water content. And this is exactly where the serious differences between anhydrite screed and cement screed begin.
Anhydrite and cement screed in comparison
Tough: cement screed
Basically, cement screed is nothing more than a fine mixture of cement and sand. Very fine quartz sand is often used to mix cement screed. However, this is not absolutely necessary. You can usually get enough usable screeds with normal construction sand. You can mix the screed yourself with a mixture of 1:4 (one part cement, four parts sand). The great advantage of cement screed is therefore that the raw screed mass can be prefabricated in any desired consistency.
The disadvantage of cement screed is that it takes a very long time to set. This is all the more serious when it is used as a cover for underfloor heating. It is very important to distinguish between “drying” and “setting”: A cement screed dries quite quickly. However, the chemical reaction process inside the mass goes even further: the concrete grains burst open when they come into contact with water and form long, curled threads. These threads get entangled with each other. This is how the enormous strength of all products with mortar is created: plaster, mortar, concrete and screed with cement are the hardest and most resistant representatives of their respective guild.
Due to the long drying process, it was common just a few years ago to only mix cement screed when it was earth-moist and to bring it into a room with a lot of manual work, then scrape it off, rub it down and smooth it. Due to the increased costs for craftsmen, however, this process is hardly used anymore. Today, liquid floor screed is standard. This is also not a problem with anhydrite screed. However, liquid cement screed takes a particularly long time to be reliably covered. Only after 28 days is the screed set to the point where floor coverings can be laid. Until then, it must not be covered so that it can “breathe” unhindered. If it is covered too early, it will promote mold under the covering.
The hardness of the cement screed is very helpful for high-strength coverings. However, it also has a disadvantage: the screed tends to crack. That is why it makes sense to work in a reinforcement fabric for larger areas. A thin braid of galvanized wire is sufficient to safely dissipate the tension in the screed.
However, a particular advantage of cement screed is its insensitivity to water. It is so stable against penetrating moisture that it can also be used outdoors. It is therefore ideally suited as a leveling layer in garages, carports or as a tile base for terraces.
Warm and elastic – anhydrite screed
Behind the unwieldy word “anhydrite” is nothing more than simple gypsum. As with plaster, anhydrite is very popular mainly because it is easy to work with. This also distinguishes the anhydrite screed: It is extremely easy to install. Anhydrite screed can only be mixed as a liquid screed. Then it is simply poured out and distributed a little. The raw screed compound takes care of the rest: it levels itself out and penetrates even the smallest cracks.
The anhydrite screed is therefore particularly popular in professional house construction: it is quickly installed and completely dry within a few days. The four-week wait is therefore not necessary with this type of screed. Underfloor heating can also be used to speed up drying without any problems. The anhydrite screed does not crack as easily as the cement screed.
However, a huge problem with anhydrite screed is its sensitivity to moisture. It absorbs penetrating moisture like a sponge. If this moisture is not removed quickly enough, the screed begins to rot and dissolve. The compressive strength is immediately greatly reduced with wet anhydrite screed. It is therefore not suitable for the bathroom. Likewise, it is simply not applicable outdoors.
Mix anhydrite screed and cement screed?
One could now come up with the idea of mixing cement and gypsum screed in order to obtain the advantages of both building materials. However, exactly the opposite will be achieved: gypsum acts as a setting retardant on cement. If only a small amount of gypsum is added to a cement mix, the mass will never harden. You just produce waste.
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Costs for cement or anhydrite screed
A sack of flowing screed based on anhydrite costs around 9 euros in a 40 kg sack. That is enough for approx. 2 square meters of flowing screed with a thickness of one centimeter. Higher structures require more material.
A sack of cement screed costs almost the same and is just as productive. 20 kilograms of screed is enough for one square meter with a thickness of one centimeter. A thickness of approx. 3-4 centimeters must be expected for underfloor heating.
Do it yourself or have it done?
The installation of the screed is not too difficult, but very messy. The screed is mixed in a tub or pumped from a silo into the rooms.
When processing screed, however, care must be taken to protect the eyes. Cement in particular is very dangerous for eyesight. In case of contact with the eyes, rinse immediately and consult a doctor. This danger is largely avoided by wearing protective goggles.