What concrete mortar is needed for floor screed: characteristics, brand and class

For building projects, selecting the appropriate concrete mortar for the floor screed is essential to guaranteeing a sturdy and level foundation. Essentially a layer put on top of a concrete slab, floor screed provides a smooth foundation for different types of floor finishes, such as carpet, wood, or tiles. The strength, leveling qualities, and general quality of the screed are directly impacted by the type of concrete mortar that is used.

When choosing concrete mortar for floor screed, a number of factors are considered. Among these is the mix composition, which is normally made up of water, sand, and cement. The strength and workability of the mortar are determined by the ratio of these ingredients. Higher cement content in floor screed mixes results in greater strength and durability, which are necessary for withstanding regular wear and load-bearing demands.

When selecting concrete mortar, brand reputation is also very important. Reputable brands frequently have a track record of producing trustworthy building materials. They provide mortars that are tested for performance and adhere to industry standards, guaranteeing consistency and dependability in your building projects. Reputable companies frequently offer advice and technical support, which is very helpful in getting the best outcomes.

Another important factor to consider is the classification of concrete mortar. Mortars are categorized C15, C20, and C25, which represent the megapascals (MPa) of strength that the concrete can withstand following a 28-day curing period. A higher class, like C25, is usually advised for floor screed applications in order to support the weight of furniture and floor finishes without eventually settling or cracking.

In conclusion, choosing the best concrete mortar for floor screed requires taking into account the strength classification, brand dependability, and mix composition. These elements guarantee that the screed not only offers a level surface but also endures the rigors of regular use. Making informed decisions will enable you to provide your building projects with a long-lasting and stable foundation that will guarantee functionality and long-term satisfaction.

Concrete Mortar Type Characteristics, Brand, Class
Traditional Sand-Cement Screed Commonly used for its affordability and simplicity. Typically composed of cement, sand, and water. Brands may vary, but ensure it meets local building codes.
Anhydrite (Calcium Sulphate) Screed Offers improved drying times and can be thinner than traditional screeds. Brands like Gyvlon or Isocrete provide options with specific classes for different load-bearing capacities.

Required characteristics

To create a floor screed, you must understand the fundamentals of concrete that guarantee its performance qualities:

  • Compression or tension class (Rb or Rbt).
  • Frost resistance grade (F).
  • Waterproof grade (W).
  • The particle size distribution of coarse or fine aggregate, which affects the performance characteristics of the mixture.
  • Chemical composition of coarse or fine aggregate. Depending on the composition and volumetric weight of the aggregate, concrete is divided into light and heavy.
  • Presence of plasticizers and other additives.
  • Mobility, which determines the technology and method of installation (from P0 to P4). Determined by the presence of additives and the water-cement ratio.

The technical properties of each ingredient used in the mixing process have an impact on the properties of the final concrete mixture.

Concepts for classification

The terms "class" and "grade" of concrete are frequently confused by non-technical users, which can result in mistakes and misunderstandings when ordering finished goods or buying ingredients. Below is a detailed description of the variations between the classes and grades of concrete mixture.

Class

A material’s concrete class is a mechanical and physical property that establishes its resistance to collapsing when subjected to outside forces. Two foundational classes exist:

  • Compression – Rb. Denoted by the Latin letter B and a digital index. Concrete classes B10, B12.5, B15 and B20 are most often used for screeding. The numbers mean the compressive strength of the material – 131.0, 163.7, 196.5, 261.9 kgf/cm 2, respectively. Strength indicators are taken according to table SP 63.13330.2018 “Concrete and reinforced concrete structures”.
  • Tensile – Rbt. The class designation is identical to the previous one, with the difference in the index – Bt. The most common characteristics for a subfloor are Bt1.2, Bt1.6, Bt2.0, which means the material’s resistance to axial tension until a force of at least 15.7, 21.0, 26.2 kgf/cm 2 is achieved . These indicators can be found in the same regulatory document.

Differing nomenclature causes confusion between class and brand. The primary ingredient in concrete is cement, a binder that guarantees the aggregate’s adherence to the stone structure and is identified by a strength grade M and numerical index.

For instance, cement grade M150 is used for concrete classes B10 and B12.5, M200 for B15, and M250 for B20. Manufacturers of finished goods may therefore approve an application with the notation "Heavy concrete class B20 or M200." However, the term "Concrete grade M200" is regarded as inaccurate from a scientific perspective.

Brand

Concrete has its own grade in addition to classes for compression and tension, which is taken into consideration when the material is manufactured. The following categories comprise brands that influence concrete screed performance characteristics based on environmental factors.

  • Frost resistance. This indicator is denoted by the Latin letter F and a numerical index. The numbers indicate how many cycles of passing through the zero mark during the cold season the material can withstand. For the subfloor, grades F50, F75 or F100 are used, which is quite sufficient even for use in an unheated room.
  • Waterproof. The brand is designated by the Latin letter W and an index, similar to the previous version. The number means the number of atmospheres (atm.), which the concrete structure can withstand without through penetration of moisture, in case of immersion in water. There are brands W2, W4, W6, …, W12, but for floor screed, as a rule, values ​​no higher than W are used

Following testing on cube samples, the plant that produces and supplies concrete issues a quality passport that lists all of the classes and grades of concrete, such as "Heavy concrete, B15, Bt1.6, F74, W4".

Requirements

Before sending the working drawings to the construction site, designers specify different aspects of the rough finishing element for indoor floor screeding because this structure is subject to specific design and operational requirements.

Depending on location

An essential factor in determining the composition, mechanical properties, and physical attributes of the concrete mixture is the location of pouring:

  • Living rooms of apartments and private houses – the calculated load on the finished floor in such premises does not exceed 100 kg/m2 . The intensity of use and humidity are low, which makes it possible to use a screed without coarse aggregate, or from concrete with characteristics not higher than B10, Bt1.2, F50, W.
  • Bathrooms, kitchens, laundry rooms, saunas, swimming pools and other auxiliary spaces in residential buildings. The loads in such rooms remain the same, but increased humidity requires increasing the waterproof rating to W4 – W.
  • Staircases, balconies, open terraces, loggias, porches – such spaces are subject to higher operational loads, or the weight of the snow cover is added to the standard loads. In addition, temperature changes are possible, which requires increasing the class and grade of frost resistance. Recommended screed parameters for such spaces are B 12.5 – B15, Bt1.6, F75 – F100, W.
  • For office premises, a design floor load of at least 150 – 200 kg/m2 is accepted, which requires a concrete class of at least B15, and Bt1.6. Indicators for frost resistance and water resistance are taken to be the same as for residential premises.
  • For public buildings with a large flow of people – shopping centers, cinemas, sports clubs, the grade and class of concrete for the subfloor are accepted as increased – at least B20, Bt2.0, F750, W.
  • For industrial facilities, the design load on floors depends on the characteristics of the technological process. In some cases, higher grades and grades not listed above may be accepted, for example, B25, Bt4.0, F150, W.

Often, the project chooses the type of concrete for a structural rough-finishing element based on computations, technical drawings, and space-planning solutions.

From technology

The kind of constructive element, the styling theology, and other characteristics directly affect the composition of the concrete mixture for screed as well as its mechanical and physical qualities:

  • Wet – classic screed, mixed directly on the installation horizon, or on the mixing plant. When choosing technical characteristics, all the indicators given above are taken into account – tensile and compressive strength, frost resistance, water resistance, mobility.
  • Semi-dry – a more modern type of screed, which is mixed in a special device and supplied to the mounting mark by a pump. It is a cement-sand mortar of minimal mobility (P0), which is reinforced with fiberglass.

This material’s absence of crushed stone, or coarse aggregate, is one of its defining characteristics.

When placing an order, consideration is given to the granulometric composition of the sand, the percentage of fiber fiber, and the cement brand, which is typically M400 or M500. Plasticizers are occasionally added to raise the F and W values.

  • Chernovaya-if, before the device of the finish finishing layer, it is supposed to use a bulk floor or a second layer of screed, a large aggregate may be present in the design, and the main indicator of such an element is to ensure all the required physical and mechanical properties. Thus, the optimal parameters for such material are B15 and higher, F50, W4 – 6.
  • Finish screed – must be perfectly flat, laid on top of the subfloor, used for the installation of a finishing coating – tiles, laminate or linoleum. The main indicator of this design is the absence of coarse aggregate and the use of a cement binder with the maximum grade – M500.

In addition, it’s critical to maintain the hardening time, pay attention to ingredient proportions, and adhere to laying technology when building a screed. The establishment of the requisite climate conditions is a crucial prerequisite, since cement is a hydraulic binder and gets stronger in a humid atmosphere.

Dependence of concrete performance on the method of its production

The production process, location, and use of specialized equipment all have a significant impact on the technical properties of concrete, as it must withstand the recipe and maintain the appropriate kneading intensity during manufacturing.

From scratch by hand

The cheapest and riskiest method of producing concrete for screed. In order to meet design requirements, the master must consider several subtleties:

  • Cement should be purchased with higher characteristics than required by the project or technological map. Thus, if a mistake is made during manufacturing, the strength parameters of the finished screed will not be affected.
  • You should order washed river sand based on quartz. Thus, the risk of the presence of clay components is eliminated, which will significantly improve performance indicators.
  • All ingredients are added in stages, according to the recipe. The optimal ratio of cement, sand, crushed stone and water is 2:5:9:1. First, cement and sand are mixed, then crushed stone is added. Когда сухая смесь достигнет однородной консистенции, вода добавляется порционно, до получения подвижности и начала реакции с цементом.
  • Mixing should not be done manually, but in a special electrical device – a mobile mixer. This will allow you to achieve a homogeneous consistency of the mixture.

The master obtains the essential concrete properties by paying attention to the process chart and adhering to these recommendations. It is quite difficult to obtain a high-quality mixture made using this method in the event of a violation.

Watch the video for more information on how to self-prepare a screed solution:

In production

The primary function of BSUs, also known as concrete mixing devices, is to produce ready-mixed concrete. These businesses also possess automated lines equipped with CNC and automation systems. Ingredients are dosed strictly according to the given boundary parameters using electronic scales.

Errors can only occur when inferior parts are used. Given the abundance of rival businesses in every area of the Russian Federation, the plant typically produces concrete with the specified technical attributes.

From dry ready-made concrete mixes

Utilizing a prefabricated sand-cement blend is an additional method for creating screeds intended for use in residential and public areas. In such instances, the buyer can be certain of the high quality of the sand and the necessary ratio of cement to fine aggregate when buying the composition if there is a quality certificate.

The master can obtain concrete for the screed with the necessary properties, and the risk of error and technological violation is greatly decreased. These mixtures typically enable you to obtain a concrete class of at least B15–B20, which influences the structure’s performance characteristics following installation.

The frost resistance grade is contingent upon the cement’s parameters and is limited to the one specified on the bag containing the dry mixture. On the other hand, the F and W indicators can be raised to 100 cycles and 6 atm, respectively, when plasticizers are added.

We go into the fundamentals of selecting the best concrete mortar for floor screeds in this article. We examine the composition, strength, and workability of mortars as well as their essential qualities that render them appropriate. Making an informed choice requires knowledge of the various brands that are available as well as their reputations. In addition, we make clear the significance of mortar classes and how they connect to the particular demands of your project, guaranteeing performance and durability. With this knowledge, you can choose the best concrete mortar to create a level and sturdy floor, whether you’re building a new home or remodeling an existing one.

Tips for choosing: what is better to fill?

Selecting the right material composition is crucial when making concrete for screed because too strong a mixture won’t be able to provide the necessary operational parameters, and too little strength will result in excessive expenses.

The following elements must be considered when selecting a concrete brand and class for a subfloor:

  • Type and functional purpose of premises, on which the operational load and class of concrete depend, respectively.
  • Temperature and humidity conditions in the room, on which frost resistance and water resistance grades depend.
  • Features of the technological process.
  • The composition of the screed cake is the presence of a floating floor structure, heat and sound insulation materials. If there is an elastic base under the screed, the strength characteristics of the concrete should be higher – at least B20.
  • Type of finishing coating – when installing ceramic tiles, the quality of the fine aggregate should be higher to avoid cracking of the material.
  • Place of installation of the screed – when installed in street spaces, all characteristics must be increased.
  • In the case of installing screeds in the winter, you need to pay special attention to the air temperature at the mixing site – if the thermometer drops below + 5 o C, you should add anti-freeze additives that will eliminate the risk of water freezing until the end of the cement chemical reaction.

The structure will lose its operational qualities if the physical and mechanical characteristics of the screed’s ingredients are chosen incorrectly. As a result, the floor covering may locally collapse, develop cracks, or exhibit a distinctive crunch when walking due to material delamination.

For the longevity and functionality of your flooring, selecting the appropriate concrete mortar for your floor screed is essential. The strength and appropriateness of the mortar for different floor types are directly influenced by its properties, such as mix ratio and aggregate size. It’s critical to choose a mortar mix that satisfies the particular needs of your project, taking the environment and load-bearing capacity into account.

Regarding brands, respectable producers provide a variety of mortar mixtures designed for various uses. Smooth and level floors require products with consistent performance and dependability, which are often offered by high-quality brands. Give preference to well-known brands with a track record of satisfied customers and adherence to industry standards.

The amount of cement in the mix determines the class of concrete mortar, which indicates its compressive strength. Greater strength is indicated by higher classes, which make them appropriate for high foot traffic areas or heavy-duty floors. Choosing the right mortar that can endure the intended use and offer long-lasting support without cracking or settling is made easier by having a thorough understanding of the class system.

In conclusion, the type of concrete mortar you choose for your floor screed should be in line with the particular requirements of your building project. You can guarantee a long-lasting, level, and dependable floor surface by taking into account elements like mix characteristics, reliable brands, and suitable class ratings. Choosing the appropriate mortar up front improves the flooring’s structural integrity and adds to the overall durability and quality of your construction project.

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Fedor Pavlov

Interior designer, author of books on residential design. I will help you make your home not only functional, but also beautiful.

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