Screed

When Estrich ( althochdt.: esterih, Greek όστρακον ostracon shard, earthen tablets, Latin: astracum, patches), referred to the construction of the floor as a base for flooring. Screeds are appropriate depending on the type and design also called finished usable floor. The Swiss word for screed subfloor, the word " screed " where it describes the attic. A special form is the so-called "Use slash" or " view screed ". Here, the screed is also the " wear layer " without surface covering.

• 3.1 cement screeds
• 3.2 Calcium sulphate screeds
• 3.3 mastic asphalt screed

• 4.1 topping
• 4.2 screed on a separating layer or separation layer
• 4.3 screed on an insulating layer ( " floating floor " or " heated screed " )
• 4.4 Readiness for covering
• 4.5 Dry screeds
• 4.6 Advantages and disadvantages of dry screeds
• 4.7 standards

Definition

Screed layer or layers of screed material on site directly to the substrate, is laid with or without bond, or to an intermediate separation or insulation to meet one or more of the following functions:

• To reach a predetermined altitude
• Receive a floor covering
• Immediately used to be.

Screeds binder

Screeds can be distinguished according to their binders.

Cement screed (CT )

The most famous is the screed according to DIN EN 13 813 as designated CT (of Cementitious screed ) cement screed. This is a concrete, the particle size and mixture was optimized for its particular use. As a rough guide can serve the available DIY Ready- dash for home use, which has a grain size up to 8 millimeters and a mixing ratio of sand to cement of about 3:1. For industrial applications, the sand can be screened and more the surface strength can be increased by adding specific chemical additives, such as Korodur. Also, the strength of a screed classes are inspired by those of the concrete.

Under the designation, the classic thick bed is to be considered, which is also equally be measured as a CT. The CT is also in coloring, easily recognized by its reaction with acids, such as cement remover. Advantage of CT is the resistance to water after curing. The disadvantage is its behavior on insulation or separation layer. By " shrinking operations ", which are expressed during the hardening process of the screed in creep and shrinkage due to the uneven hydration, the field size in the rule must be limited to 36 m², since uncontrolled form in the construction Otherwise cracks. CT is moisture-resistant, but can lose strength in the wet state as each cementitious system.

Cement screed requires the introduction and during the solidification of a minimum temperature of 5 ° C ( even at night). During the solidification phase, the temperature shall not be exceeded, otherwise there is to be expected with strong resistance losses. The screed is against drafts and water ingress ( leaking roof, tipping out water, etc.) to protect. The draft leads through the Kapillarzug to increased hydration in the surface region. This means that a smaller volume is "up " and "down" and the screed schüsselt strong. Forced drying processes by heating lead to the termination of hydration and crystal growth. This results in a loss if the floor gets moisture, eg by water from a mortar. The accessibility depends on the type of cement (CEM I, CEM II), thickness, and environmental conditions. After 28 days the first moisture measurement can be performed.

If the cement floor to be provided with a floor covering, it must be the screed " dry enough " ( 3.1.1 of DIN 18365 - Flooring works) to be. Following a recommendation of two associations from the year 2007, the moisture measurement is to be carried out with the CM method. The so-called evidence of maturity to be reached when the screed a residual moisture content of at most 2.0 % CM ( unheated), or 1.8 % CM (heated ) has. Both the measurement method and the recommended limits are criticized; published in March 2012 after a study by the Technical Commission Building Adhesives ( TKB ) and the University of Siegen separates the CM threshold of 2 % slip mature screeds not sure of not occupying mature screeds. In this limit also wet screeds are rated as dull.

Quick strokes cement-based blends of cement with additives. There, the rules for the hardening and readiness, which depends on the nature and effect of the additional applicable. These screeds are not subject to DIN 13 813 and are regarded as special construction.

On the Stemmter cement screed is regarded as normal construction debris, provided no organic ingredients are contained > 5 %. This is based on the Regulation on the European Waste Catalogue (EWC).

Mastic asphalt screed (AS)

The anhydrous poured asphalt (AS ) ( screed Mastic Asphalt ) consists of a mixture of gravel, bitumen, sand and stone powder. As this mixture must be heated to a temperature of 230 ° C, the poured asphalt during installation is pourable and spreadable and does not need to be compressed. It can be introduced swell or joints. Its low thermal conductivity and its impact sound reducing property can cause depends on the structural requirements of the floor structure no insulation must be installed. It is water - and vapor-tight and, in conjunction with suitable bitumen sheeting or asphalt mastic sealing in accordance with DIN 18195 dar.

The AS can be installed as a topping with a bitumen membrane in hydraulically bound substrates and screeds on separating layer / insulation. Also known as mastic asphalt heated screed with copper pipes.

Before an occupancy of mineral materials (natural stone, ceramics, concrete ashlar) rule is to create a decoupling or a barrier. Mortar water is alkaline and can saponify the surface of the AS cold and impede adhesion. There is also a risk of discoloration by wandering bituminous substances. A further disadvantage is the slow motion upon heat and static and dynamic loads.

The biggest advantage of AS is the quick readiness for his disadvantage the high cost. When resilient flooring (wood, linoleum, PVC, rubber) may lead to chemical reactions with plasticizers and migratory bituminous substances without appropriate barrier layer, so that a corresponding blocking primer may be necessary there as well.

Synthetic resin screed (SR )

With the international designation of SR (of synthetic resin screed ) are synthetic resin screeds, usually referred to Epoxydharzestriche. However, polyurethane, polymethyl methacrylate and other polymers are also possible. This very expensive substrates are installed only in special cases, for example if you need short drying times or high dynamic load. The shrinkage in the polyaddition, depending on the product at 1-5 percent. This must be considered when selecting the installation material. SR is water resistant. Disadvantages are potential hazards from the hardener, such as bisphenol A. These are also suspected of causing infertility. Also a change in the fire classification, and overall design may be possible. Condensation polymers such as polyesters, are not suitable due to the high shrinkage rate.

On the Stemmter resin screed is considered hazardous waste and must be declared in accordance with the waste disposal company.

Calcium sulphate screed (CA )

As calcium sulphate screeds (CA ) screeds are referred to, in which the binder consists of calcium sulfate and / or anhydrous calcium sulfate ( anhydrite so-called ). Water reactive creates calcium sulfate dihydrate (gypsum). Calcium sulphate screeds are marked according to DIN EN 13813 with CA and colloquially often referred to as anhydrite.

Due to the low shrinkage behavior have CA not the usual for CT bowls or later depressions on the edge and can be laid over a large area with few joints. They are installed as conventionally to be processed as a screed or liquid screed, are early accessible, robust and relatively insensitive to drafts. As CA -leveling floor can be also marked with CAF 18560-2 DIN. CAF have the further advantages of fast, easy to process installation, the lower thickness of the screed and the good thermal conductivity for heated screeds.

CA are not water resistant, and must not be exposed to prolonged moisture. They are therefore not suitable for use in commercial wet areas (slope, drainage ) or suitable for outdoor use. In domestic wet rooms (eg bathroom) they are protected by a composite seal.

In case of late a higher moisture mold risk than cement or Poured asphalt is to be expected.

Before cover-ing, or primer of the CA must have a residual moisture content of 0.5 %, down dry as heating screed to 0.3%. The residual moisture is determined by a measuring device CM.

On the Stemmter anhydrite is considered normal construction waste, if no organic components are > 5%.

Magnesite screeds (MA)

Magnesite screeds, MA (of magnesite screed ) is the older masons also known as Stone Wood. After 1945, cement was rationed, magnesite not. Therefore, it can be found in many old buildings. Magnesia is known to many of gymnastic competitions as " drying agents " for the hands. In 1867 it was discovered that magnesia solidified with magnesium chloride to a cement- like mass. MA can be easily colored and was often mixed with wood flour or wood chips. Its particular advantage is the ease of use and as " conductive finished floor ." Its major disadvantage is the sensitivity to moisture and corrosive to metals, as the chloride and magnesium hydroxide contained "washed out" when water is added and the MA will swell like a yeast cake. He may never come directly in contact with aqueous mortar. A typical use today is as a stroke advantage for large dry surfaces.

Fiber Reinforced screeds

To change the flexural strength of screeds, they are often reinforced with fibers. As opposed to a grating floor, for example, the existing metal AKS grating to change the strength of fiber reinforced screeds values ​​because the elasticity and bending strength depends mainly on the size of the crystals in the floor. The more and the smaller the crystals form is the hardening in fiber reinforced screeds, the greater the elasticity and the modulus of elasticity is lowered. In contrast, the contact surfaces of large crystals are much smaller and entangle and interlock to a lesser extent. In this case, however, the elasticity and the modulus of elasticity is lowered increases.

Cement screeds

Cement screeds (CT ) are reinforced with fiberglass. These fibers go no chemical or mechanical connection one with the CT. They are used to prevent the formation of large cement crystals. This results in more " crystal ", and it increases the elasticity, and the modulus of elasticity decreases.

Calcium sulphate screeds

Calcium sulphate screeds (CA ) contain many small crystals. Can be obtained by organic additives, such as flour, hair, or other organic materials have a fiber reinforcement. These additives, which are also known as crystallization nuclei, is known as " plaster sticks " or larger crystals that reduce the elasticity of the CA or can increase the modulus form.

Mastic asphalt screed

There are several variants, because the polymer chains and no crystals are formed. By the addition of steel fibers, the thermal conductivity can be changed. Addition of crosslinking agents can stabilize the floor, but with the disadvantage that a larger uncontrollable shrinkage that affects part or the entire screed, can begin.

Construction types

In addition to his role as " filling and balancing substance" is to be regarded primarily as a screed load distribution layer, under which heaters, heat and sound insulation can be located. It can also be the direct wear layer. In the construction types of screed after screed binders but is not after construction, divided or type of construction.

Topping

The topping is located directly on the concrete floor and is connected to this strong. Since all forces are transferred directly into the ground, the load capacity is through the ground, typically a concrete slab, or limited by the compressive strength of the screed. Major problem in the production of a composite screed is the correct substrate preparation, so that there are no hollows. Especially under high dynamic loads a topping is to be selected. Calcium sulphate screeds should not be deployed in conjunction, because in the absence of heating, the necessary residual moisture content of 0.5 % CM usually can not be achieved and there is a reaction with the concrete ( ettringite ).

Screed on a separating layer or separation layer

Between rough concrete and screed is a layer that does not allow connection between the components. Ideally, the screed for example slides on a two-layer polyethylene film. This requires an absolutely flat concrete floor, what is illusory in practice. The creep and shrinkage and the resulting deformation of cement in its raw may further influence the flatness. This means that the floor can not " move " may be " pinching " and at worst breaks. In an old building, the risk typically is no longer given. This type of construction is the schadensträchtigste construction. To any penetrating moisture, for example, to prevent from a erdberührenden, not cordoned concrete slab, composite seals are the best alternative because it matched a topping is much more resilient and less risky.

Screed on an insulating layer ( " floating floor " or " heated screed " )

The screed is on a PE film and this on a foam board and is laterally enclosed by insulating strips, so that no sound or heat-transferring connection to the rest of the building is ( "float "). The insulation board can be a footfall sound insulation and / or thermal insulation. Typical materials for the insulation are, for example, pressure-resistant glass or foam EPS (expanded polystyrene). Here the deformation stability of the insulating materials is a crucial factor. Floor subsidence, for example, by more than 200 kg / m² in private kitchens are one of the main causes of damage for torn kitchen countertops or flooring. In the commercial sector are dynamic loads more problematic at a floating screed. In the upper part of the insulating layer or in the mortar of a heating pavement heaters are installed or coiled tubing for underfloor heating. Legally, the standard applies to DIN 18560: Floor screeds in building industry, in addition to various leaflets of the ZDB ( Central Association of the German Construction Industry ) and BEB (German Association for Screeds and Coverings ).

• Steps for installation of heating screed

Pressure hose and discharge stand be used for the introduction of screed

To recognize is the film on which the screed is; among them is the insulation ( polystyrene)

Withdraw ( leveling ) with a long spirit level

Smoothing with wooden board

Finished screed, the beginning of the drying time

Evidence of maturity

For natural stone and ceramic deformation stability is crucial, while parquet, or soft ground, such as PVC, linoleum or rubber needs to be more attention to the moisture. For natural stone, it means that the expected shrinkage of the screed must be completed as far as possible. Experience shows that an expected residual shrinkage value of 0.2 mm / m tolerable, while a value of 0.5 mm / m is estimated as risky. In a " normal" cement screed, which was correctly processed and dried under " laboratory conditions ", one can with a CM the humidity value - identify device and connect indirectly to a large extent completed shrinkage. At too high room temperature or underfloor heating is switched on, the screed acts while dry, but is still far from ready for laying. For the mixed with water screed mortar sufficiently long drying times (including curing) are observed.

Depending on the change of air, room temperature, relative and absolute humidity, the time may greatly extend. The values ​​for the permissible residual humidity until ready for covering depends on the screed, unheated or heated construction and subsequent flooring. Forced drying may lead to an interrupted hydration and cause deformation with cracking at a later moisture entry (mortar of the top coat ).

For anhydrite increased dryness is necessary. The results from the hydric properties and Notwendigtkeit a barrier layer for later Endbelag / apply mortar. This may be in the near-surface region only penetrate and act when a sufficient penetration depth is achieved. Is there any free water on the surface, there will be no proper seal.

The values ​​given correspond to CM- %. These values ​​are determined with a calcium carbide meter ( CM device ). With additions, containing the so-called " fast-drying screeds ," can be shortened if necessary the " readiness for covering ." So-called Fast underscores are not standardized screeds, but special designs. A distinction is made between so-called hybrid lines, which are only offered as a complete ready- mix and admixtures in screeds. See also the articles in the link list. The rules for residual moisture are not usually. Here, the respective manufacturer should be consulted. The CM measurement is required by normative. In this case, a certain amount of the screed is taken from the existing floor, ground and shaken with the addition of calcium in a chemical container. The gauge pressure is measured and can be converted to CM- %. It is not a measurement, but a correlation of experience with CEM I - screeds. In CEM II _ screeds other conditions may arise.

Dry screeds

Dry screeds are a variant that is particularly suitable for dry construction. All Dry screeds are not captured normative. These are generally for special constructions that need to be specially charged. Here, the planner has a much higher responsibility or liability planning.

Dry screeds are used on the one hand in the renovation of old buildings ( wooden beams ) to avoid exposure to water. An aptitude depends amongst others, the vibration behavior of the substructure and the lining material. For example, the combination " chipboard and linoleum " substantially less problematic than " Anhydritplatten and natural stone ." Since they are dynamic processes, it makes sense to hire at a higher investment volume or commercial use, an independent structural engineers, which can calculate the expected static and dynamic loads.

In new construction or on stable substrates ( concrete slab ) is the advantage of rapid evidence by the way not to be observed drying and curing time. Disadvantages are the higher costs.

In dry screeds following materials are used: chipboard (also cement or magnesite - bound ), OSB, hardwood fiber boards, gypsum fiber boards, gypsum boards, cement screed and Perliteplatten plates. For uneven substrates, leveling is necessary, for example through a bed. This is depending on the system, for example, clay balls, plastic or other materials. A smoothing of the background would be possible with smaller bumps. Here, however, is the different expansion behavior and response to dynamic loads to be considered (building physics ). In wet areas, the load capacity is also to be considered by moisture.

Advantages and disadvantages of dry screeds

• Benefits of dry screeds: No waiting time caused by drying,
• No drying protocols
• No CM measurement necessary
• Moisture load of the building,
• Partly of lighter construction, analogous to a magnesite screeds,
• Lower construction height than conventional screeds are possible,
• Greater height differences can be compensated by lifting devices, resulting in lower weight load.
• Affected less mass in floor heating, therefore faster heatable rooms.

• Disadvantages of dry screeds: level base is required ( fill, leveling ),
• Combining design and flooring must be calculated from a building physicist, if necessary,
• Lower capacity for dynamic loads, such as wheelchairs,
• Standard tables for impact sound insulation are not applicable;
• With underfloor heating temperature limits are observed,
• The moisture sensitivity depends on the screed material and the amount of the compensation system,
• Standard tables for thermal conductivity at heaters are not applicable,
• Higher costs,
• General Special constructions with higher risk of liability for the designers and the contractors.

Standardize

The applicable standards for screeds are within the EU:

• DIN EN 13318 Screed terms
• DIN EN 13813 Screed materials - Properties and requirements
• DIN EN 13892 Methods of test for screed material and floor screeds, Part 1-8

In addition, Germany is:

• DIN 18560 screeds in building, German Application Rules Part 1: General requirements, tests and application rules
• Part 2: Concrete and heated screeds on insulation layers
• Part 3: Bonded screed
• Part 4: screeds on separating layer
• Part 7: High-stress screeds (industrial screeds )

Conformity check

A conformity check in normative collected screeds includes initial assessment and a factory production control and self-monitoring.

An initial assessment must be carried out at the start of production of the screed or making one each new product or with changes of reactants. Even a change and conversion of the manufacturer procedure requires a respective initial test. Here, the compressive strength and Biegezugfestigkeits verification and check with cement floors with a direct use of the mechanical resistance to wear.

In so-called building site screeds an examination of the delivery notes as well as a visual inspection of the reactants takes place. The manufacturing process as such must be checked at regular intervals.