We compare semi-dry floor screed, regular and dry – which is better to choose??

The success and longevity of your flooring during building and renovation projects depend on the type of floor screed you select. You may come across semi-dry, regular, and dry floor screeds as three typical options. Before choosing, it’s critical to comprehend the distinctions between each type as each has unique qualities and benefits.

Because of its affordability and workability, semi-dry floor screed—also referred to as traditional or traditional semi-dry screed—is a preferred option. It is made up of a combination of water, cement, and sand that is usually mixed in a way that makes it easy to spread and level. When a level and smooth surface is required prior to the application of final floor finishes, this kind of screed is frequently used in residential and commercial buildings.

Regular floor screed, also known as traditional wet screed, is applied to the floor surface and leveled to produce a smooth finish. It is made of a cement and water mixture. In comparison to semi-dry screed, this method uses more water, which results in a wetter consistency that may take longer to properly dry and set. Regular screed is frequently used in projects that call for a particular finish or thicker layer, like those in industrial settings or places that see a lot of traffic.

Compared to conventional techniques, dry floor screed—also referred to as dry mix or flowing screed—offers a number of benefits. It just needs water added on location and is made of a pre-mixed mixture of sand, cement, and additives. This kind of screed self-levels and is pumped onto the floor, saving a lot of manual labor and speeding up the building process. For projects that prioritize quick installation and little disturbance, like contemporary residential developments or renovation projects, dry screed is perfect.

Characteristics of species

The following three types of high-strength and effective screed are currently used for a variety of purposes during construction, installation, repair, and finishing work in buildings:

  • Wet.
  • Semi-dry (hereinafter referred to as p/s).
  • Dry.

The strength, style, materials used, and other characteristics of each of these varieties vary; these differences are covered in more detail below.

Semi-dry

A semi-dry screed is a building and finishing structure that is placed over the floor, foundation slab, or ground floors. It is composed of a dry mixture of sand and cement that is just slightly wetted, just enough to initiate a chemical reaction with the binder component. This screed is applied by machine, using a portable mixing device, pump, and dispenser mounted on the installation horizon, to ensure stability of bonds with binder particles and fine aggregate. It can also be reinforced with fiber fiber to increase strength.

A "helicopter," or specialized blade apparatus with abrasive contact planes, is used to smooth such a screed.

Dry

In addition to leveling the floor slab before laying the floor covering, a dry screed is a building component that enhances the performance characteristics of the floor in any dry room.

This kind of screed is constructed from bulk dry porous low-density material that insulates against heat and sound:

  1. expanded clay;
  2. perlite;
  3. slag;
  4. expanded vermiculite or other natural compounds.

Inert bulk components are deposited directly on top of the floor slab; the design dictates the fill’s thickness.

The bulk materials are carefully leveled, and then slabs of cement, sand, plasterboard, plywood, or other material are placed on top to create a level surface that is ready for the application of a finishing coating.

Wet

The trickiest, most labor-intensive, yet most dependable and long-lasting construction is wet concrete, also known as cement-sand screed. arranged using cement-sand mortar’s coarse aggregate and liquid concrete, with a mobility degree of P2 to P3.

Positioned in line with beacons and strengthened with composite or steel mesh. Forms a dependable, unbreakable monolithic waterproof coating with the best performance qualities after hardening in 7 to 25 days.

Since the structure can be used in all types of residential or public premises, including those with higher temperatures and humidity conditions, thermal insulation and waterproofing layers are frequently placed beneath the screed, ensuring its widespread use in actual use.

To assist you in selecting the best floor screed for your building or renovation project, we examine and contrast the benefits of three popular varieties: semi-dry, regular, and dry. Every variety provides unique advantages: Semi-dry screed is appropriate for a variety of floors because it strikes a balance between strength and ease of application. Regular screed, which is frequently used in traditional building, offers a dependable, affordable option but necessitates longer drying times. Conversely, dry screed is best suited for expedited projects because it requires less drying time and can be installed quickly. You can choose an option that fits the particular requirements of your project as well as your financial constraints by being aware of the features and uses of each type.

Main differences

The strength, complexity of the device, suitability for heated floors, and other materials and engineering tools of the three types of screeds mentioned above vary. Their recommended service lives and technical specs vary from one another. Next, you can view a thorough comparison of these subfloor construction types based on various criteria.

Strength

  1. Semi-dry: the strength of this screed depends on the brand of cement binder, its amount in the semi-dry mixture, as well as on the type of aggregate and the presence of reinforcement. As a rule, the mechanical compressive strength of such a screed ranges from 14 – 15 MPa to 17 – 18 MPa, when using cement grade M400 – M500.
  2. Dry: this screed is installed only in residential or office dry premises, due to its insufficient mechanical strength, which is no more than 12 – 15 MPa, regardless of the type of backfill and the category of sheets of the top covering of the subfloor in the room.
  3. Wet: considered the most durable and reliable subfloor construction. Bearing capacity under compressive static loads can reach 18 – 19 MPa (for M300 cement), 20 – 22 MPa (M400) or 24 – 27 MPa (M500).

Durability

  • Semi-dry: despite the fact that suppliers of this material often state that, with proper care and thorough adherence to technology during installation, it can last from 35 to 40 years or more, the actual service life of such a structure, as a rule, does not exceed 25 to 30 years in rooms without dynamic loads.
  • Dry: the weakest screed, which in residential premises can last up to 15 – 20 years, and in public premises – no more than 10 – 12 years, without the need for major repairs or replacement.
  • Wet: reliable design, the durability of which exceeds 30 – 35 years or more, depending on the thickness, grade of cement, mechanical characteristics, and operating conditions.

Resistance to temperature changes

  1. Semi-dry: the type of screed in question has a relatively low temperature resistance, the recommended operating range is from -30 o C to +40 o C.
  2. Dry: there is no water vapor in this screed, and therefore its frost resistance largely depends on the resistance to temperature changes of bulk inert materials or covering sheets. Most often, the recommended temperature range for this screed is from -25 o C to +35 o C.
  3. Wet: the most reliable and resistant to temperature changes design, which is easy to operate without damage from -40 o C to +50 o C. However, experts warn that such indicators are achieved only with complete evaporation of water during the screed’s strength gain, as well as in the absence of wet processes in the room that contribute to moisture saturation of concrete or hardened porous cement-sand mortar.

Moisture resistance

  • Semi-dry: average moisture resistance – the maximum value is W2, which is explained by the presence of a large number of pores in the structure of the screed. At the same time, if a liquid water repellent was added to the composition of the semi-dry substance, which closes the pores, then the water resistance and moisture resistance of the finished structure increases many times over.
  • Dry: unfortunately, the porous components of dry screeds are characterized by insignificant moisture resistance, and such structures are strictly not recommended for use in wet rooms – in bathrooms, showers, swimming pools, kitchens. And also in open spaces where the floor covering may be exposed to aggressive precipitation.
  • Wet: the water resistance of such screeds depends on the quality and quantity of the cementitious binder ingredient, as well as on the presence of plasticizers and modifying additives. With cement grade M300 – M400, the screed has a water resistance index of W4, but, with the addition of water-repellent components, this parameter can be increased to W6, in connection with which, such a design is in demand when installed in open street spaces, as well as in rooms with high temperature and humidity conditions.

Thermal conductivity

  1. Semi-dry: average thermal conductivity – the material has moderate porosity due to coarse-grained sand, and therefore, when installed on top of floors in ordinary living rooms, only a penofol backing is required for the final coating. The average thermal conductivity is 0.42-0.47 W/m o K.
  2. Dry: this parameter for a bulk structure largely depends on the type of inert materials and their individual characteristics. For example, the highest thermal conductivity is achieved for expanded clay, but for slag backfill or perlite granules it will be slightly lower. The average heat transfer resistance index, according to laboratory studies and field measurements, varies from 0.14 to 0.19 W/m o K.
  3. Wet: classic high-strength concrete or cement-sand construction is one of the densest, with a minimum number of pores. In this regard, its thermal conductivity index is the lowest – from 0.6 to 0.9 W/m o K. Such a screed almost always requires the installation of effective insulation from extruded polystyrene foam, expanded clay or other insulating materials, which are poured or laid under the reinforced plastic composition of the subfloor, regardless of the type of room.

Floor loads

Semi-dry: The screed can support the following kinds of loads and has a higher load-bearing capacity:

  • For residential premises – from 70 to 150 kgf/m2 .
  • For office buildings – up to 200 kgf/m2 .
  • For commercial areas with low intensity of application of dynamic or vibration loads – up to 250 – 300 kgf/m2 .

Dry: The screed is primarily used in warm, dry residential buildings with loads on floors that don’t exceed 100 to 120 kgf/m^2.

Wet: Due to its ability to support the following kinds of loads, this screed can be set up and utilized in practically any space:

  1. On M300 cement:
  2. Apartments and private residential buildings – up to 150 kgf/m2 .
  3. Office premises – up to 200 kgf/m2 .
  4. Commercial or public facilities – up to 250 kgf/m2 .
  5. On M400 cement:
  6. Shopping centers and shops – up to 300 – 400 kgf/m2 .
  7. Sports complexes, swimming pools – up to 300 – 350 kgf/m2 .
  8. Industrial buildings with gentle operating conditions – up to 400 kgf/m2 .
  9. On M500 cement:
  10. Large shopping centers with a large flow of people – up to 600 – 700 kgf/m2 .
  11. Industrial buildings of any scale, regardless of the nature of the production processes inside – up to 800 – 1000 kgf/m2 .
  12. Reinforcement mesh made of steel with a cell of 100 x 100 mm and a rod diameter of 3 to 4 mm, also allows you to increase the calculated load on the finished floor to 30% – 40%, without the risk of loss of load-bearing capacity.

Device complexity level

  • Semi-dry: installed by machine at a speed of up to 10 m 2 of finished coating per hour, subject to a thickness of up to 100 mm. As a rule, installation services for semi-dry screeds are provided by contractors who have specialized equipment on their books, as well as labor. In this regard, the screed is installed in a standard 2-3 room turnkey apartment, along with reinforcement, within 1 day.
  • Dry: arranged by manually pouring ready-made inert dry materials onto the surface of the floor slab, after which this leveled layer is also covered with ready-made factory-made slabs. In this regard, this structure can be installed even with your own hands or by unskilled labor, without the use of special equipment, lengthy and labor-intensive wet processes, accompanied by prolonged polymerization, hardening and development of design strength. In this regard, dry screed is considered one of the easiest finishing structures to install.
  • Wet: a water-based plastic composition is mixed in a special mixer, after which it is placed in a pre-prepared formwork between the beacons and smoothed, vibrated and modified with various semi-professional tools. Wet screed is considered the most difficult to prepare, lay in the design position and care for, therefore, it is recommended to entrust this work only to professionals.

Required thickness

Half-dry:

  • Unreinforced structure – up to 50 mm.
  • Semi-dry screed reinforced with fiber – up to 70 – 80 mm.
  • Reinforced with fiber in combination with steel mesh – from 100 mm and more.

Desiccated:

  • Thickness of backfill of simple screed in an apartment – from 40 – 70 mm.
  • Thickness of the top coating of the subfloor structure – from 15 to 30 mm.
  • Total recommended thickness of dry screed – 80 – 100 mm.
  • The thickness of dry screed, subject to laying inside the bulk layer of pipe engineering communications, is determined by the project, but, as a rule, exceeds 90 – 100 mm.

Wet:

  • Ordinary leveling cement-sand screed, without reinforcement – ​​up to 40 – 50 mm.
  • Standard concrete screed with coarse aggregate in its composition, without reinforcement – from 50 – 70 mm.
  • Reinforced cement-sand screed – from 60 – 100 mm.
  • Reinforced concrete screed – from 80 – 120 mm.

Areas and places of application

  1. Semi-dry: this design is recommended for use in all types of residential and office premises, as well as commercial facilities with low intensity of operation and in the absence of increased loads, vibration, shock or other dynamic influences.
  2. Dry: given the low load-bearing capacity, this screed made of bulk materials is primarily used only for dry residential or office premises with minimal operating loads, in the absence of vibration or impact, as well as high air humidity.
  3. Wet: this screed is considered universal and, depending on its thickness, the presence or absence of reinforcement, as well as the brand of the main binding components, can be used in both residential and public, commercial, or industrial buildings and structures with virtually no restrictions. This type of rough floor covering in rooms is calculated under the influence of static or dynamic operational loads with the selection of components, class and grade of concrete, or cement-sand mortar, and is taken into account in the detailed design for the finishing of premises for various purposes.

Compatibility with heated floors

  • Semi-dry: most often, suitable for joint use only with directional infrared mats, since the heating cable or pipe communications with the coolant cause gradual destruction of the screed structure.
  • Dry: heated floors in such subfloor structures can only be used if they are installed on top of protective flat sheets. This is due to the increased energy efficiency of the main materials of the dry screed backfill, which leads to insufficiently efficient heat transfer of heating energy from the coolant in the exploited space of the room, if the pipe or cable communications of the heated floor are laid in the body of the backfill.
  • Wet: this screed has increased thermal conductivity, which makes it possible to easily install pipe or cable heated floors inside it, as well as lay infrared mats on top of such a structure if a layer of foam foam contour line with a filtered heat-reflecting membrane is placed under them.

Finish options

  1. Semi-dry: the type of screed in question is considered absolutely universal in terms of compatibility with most finishing coatings. It is ideally combined with porcelain tiles, carpet, laminate, parquet boards and block parquet, as well as linoleum and other types of polymer materials. The only restriction for this design of the draft floor is paving slabs and other types of street coverage, pedestrian paths or driveways, sports, or playgrounds.
  2. Dry: dry screed is an ideal base for laminate, parquet, plank flooring, as well as linoleum and carpeting. However, due to increased elasticity and deformability, this material is not recommended for use when installing porcelain stoneware or other tiles in wet rooms, as well as in kitchens, hallways or corridors, since the upset coating can easily crack even with slight deflections of the base under them.
  3. Wet: this type of screed is characterized by increased rigidity and excellent performance properties. In this regard, it can be used for the installation of both polymer and natural wood or mineral clay, ceramic finishing coatings, outdoors or indoors, regardless of the category of temperature and humidity conditions or operational parameters.

Cost of materials per m2

In this instance, it is important to remember that the thickness of the subfloor structure affects how much primary and auxiliary material is needed. Regarding this, the components, their percentage, and their absolute content in the final building material are calculated as follows for a 100 mm screed thickness (i.e., for every 1 m 2 of screed surface, the total volume of the finished substance is 0.1 m 3).

Semi-dry:

  • Cement of the M400 brand – M500 – up to 40% – 45%, that is, up to 0.045 m 3 . Considering that the density of the cement is about 1200 kg/m 3, the total mass of this hydraulic binding in 1 m 2 of the finished mixture is 0.045 x 1200 = 54 – 55 kg.
  • Sand of medium size, quartz – up to 50% – 55%, or up to 0.055 m 3, volumetric weight of sand – 1600 kg/m 3 . That is, the mass fraction of this substance is 0.055 x 1600 = 88 kg per 1 m 2 screed.
  • Aramid reinforcing fiber -fiber – up to 0.5% – 0.8%, or up to 1 kg per 1 m 3, in terms of 1 m 2 structures, with its thickness 100 mm, 0.1 kg, or 100 g of this composite material.
  • Plasticizers, anti -control or modifying additives – up to 0.3 – 0.5 liters for each 1 m 2 finished screed 100 mm thick.

Desiccated:

  • If the screed is performed with a thickness of 100 mm, then backfill of dry inert materials accounts for up to 80 mm, or 0.08 m 3 . Based on expanded clay gravel, the density of which is about 600 kg/m3, that is, for this example, the screed will require 0.08 x 600 = 48 – 50 kg of expanded clay.
  • Each filling of inert materials in the dry floor screed is covered with aligning sheets of OSP, chipboard, GKLV and other products, as well as the CSP – special “floor elements” from the manufacturer Knauf, which have a core ending to conjure parts of the corner of the black structure “in the castle”. The consumption of these materials is completely identical to 1 m 2 of the finished screed, and the density and mass vary from 6 to 12 kg per 1 m 2, with a thickness of 12 to 20 mm.

Wet:

  • Cement of the brand M300 – M400 – up to 30% – 40%, or 0.03 – 0.04 m 3, from 36 to 48 kg per 1 m 2 .
  • Sand of medium size, on quartz, or washed river-from 30% (in the presence of a large aggregate-for concrete screeds) to 45%-50% (in the absence of a large aggregate-for cement-sand screeds), that is, from 0.03 up to 0.05 m 3, or from 48 to 80 kg per 1 m 2 of the finished structure.
  • Crushed stone (if there are such requirements in the project) – from 25% to 30%, or from 0.025 to 0.03 m3 . Considering that for thin floor screeds, fine granite crushed stone with a fraction of up to 10 – 20 mm is used, and its bulk density is about 1800 kg/m3 . The total mass of this inert material in 1 m2 of screed is from 45 to 55 kg, but this figure may vary, depending on the actual granulometric composition of the granite components.
  • Plasticizers and modifying additives in such a screed do not exceed 3 – 5 liters per 1 m 3, or up to 0.5 liters per 1 m 2 .
  • Water is added according to consistency, in small doses, and its total amount can be from 40% to 50% of the total volume of cement (for mobility P2 and P3, respectively).

Average prices for work per m2

Half-dry:

  1. "Full construction":
  2. Thickness up to 70 mm, total area of ​​premises up to 100 m2 – from 500 – 550 rubles. for 1 m 2 .
  3. The same, but for an area of ​​more than 100 m2 – from 450 – 500 rubles. for 1 m 2 .
  4. Thickness from 70 to 120 mm, on an area up to 100 m2 – from 600 to 650 rubles. for 1 m 2 .
  5. The same, but for an area of ​​more than 100 m2 – from 550 – 600 rubles. for 1 m 2 .
  6. Only work, excluding materials and depreciation equipment:
  7. Thickness up to 70 mm – from 70 – 100 rubles. for 1 m 2 .
  8. Thickness up to 100 mm – from 100 – 120 rubles. for 1 m 2 .
  9. Thickness up to 150 mm – from 150 – 200 rubles. for 1 m 2 .

Desiccated:

  • Filling capacity up to 80 mm, covered with Knauf “floor elements” – from 150 – 170 rubles. for 1 m 2 .
  • Filling capacity up to 120 mm, covered with the same materials – from 200 – 250 rubles. for 1 m 2 .
  • Increase in cost when covered with plywood or other universal sheets, which are subject to cutting and sealing of seams, since they do not have interlocking connections at the ends – up to 20% – 30%.

Wet:

  • Non-reinforced structure for beacons, thickness up to 50 mm – from 100 – 150 rubles. for 1 m 2 .
  • Reinforced structure for beacons, thickness up to 100 mm – from 140 – 180 rubles. for 1 m 2 .
  • Reinforced structure along beacons, arranged on top of insulation and other layers of the pie, layer thickness from 80 to 120 mm – from 200 to 220 rubles. for 1 m 2 .

Which option is suitable for different rooms??

All of the above-mentioned subfloor designs are best suited for particular locations, and in certain overused areas, they might not be appropriate because of the mismatch between the functional specifications and the technical attributes of the materials, which has a major impact on the screed’s longevity.

The areas of application and suggestions for installing a particular kind of screed in a building for a variety of uses are covered in detail below.

With high humidity

Dry fill materials should not be used in bathrooms, kitchens, swimming pools, showers, or any other high-humidity area where the screed is installed because they absorb water quickly and readily.

Wet concrete or cement-sand screeds are the best materials for these types of situations, as are semi-dry constructions, as long as the plastic semi-rigid mixture has additives that repel water to seal large pores that allow water to seep through.

A private house

The material used to make the load-bearing span structures or other structural frame elements is a crucial consideration when installing screeds for private homes. In particular:

  • For wooden houses – bulk dry screed.
  • For brick houses with prefabricated or monolithic floor slabs – wet cement-sand or concrete screed.
  • For block houses made of aerated concrete blocks with monolithic span structures, a wet screed with a mixture mobility of no more than P-2, or a semi-dry structure is recommended.
  • For buildings on a metal frame with sandwich panels and floors made of profiled galvanized sheets – in this case, it is necessary to ensure the transfer of a minimum load to the span structure, as well as to the crossbars and racks of the structure"s skeleton, and the best option would be to construct a dry screed.

A working design that considers the needs of the particular space being used in relation to the technical properties of the screed ultimately determines whether or not screed is used in the building for a variety of purposes in a private residential structure.

Apartment

Experts advise the following kinds of floor screeds for a typical residential apartment, which has multiple rooms used for different purposes:

  • Dry – living rooms, halls between these rooms.
  • Semi-dry – universal use, except for cold circuit zones.
  • Wet – can be used in all areas of the apartment, including bathrooms, kitchens, hallways, as well as balconies, loggias, terraces, verandas and other cold circuit spaces.

To ensure the best performance qualities and structural durability, it would be ideal to combine several types of screed in one apartment: wet for cold spaces, semi-dry for bathrooms, hallways, and kitchens, and dry for living rooms.

Garage

The garage serves as more than just a technical space with intense static and dynamic loads on its floor covering.

Additionally, there are stricter requirements for the frictional and chemical resistance of practically all finishing elements in the garage.

Furthermore, under the demanding operating conditions of a garage block or parking space, many garages are currently unheated, which places additional requirements on the property to ensure increased resistance to large changes in temperature and humidity conditions.

Considering the aforementioned aspects, wet device only recommended screeds should be used for all categories of garages. Additionally, the cement binder component needs to have a factory grade of at least M400 – M500. Installing a concrete screed with a strength class of B15 and above, frost resistance grades F75, water resistance grades W6, and more would be the best choice for such a room.

The subfloor structure of this technical room should last the owner of the room for at least 15 years before needing to be replaced or undergo costly major repairs to fix areas of delamination, chips, cracks, and other flaws.

Useful video

Further details regarding the subject matter of the article in the video:

Semi-Dry Floor Screed Regular Floor Screed
Uses less water, faster drying time Higher water content, longer drying time
Good for underfloor heating systems Versatile but slower to set
Requires skilled installation for consistency Suitable for most applications with proper curing

The decision between semi-dry, regular, or dry floor screed is influenced by a number of variables specific to your building or remodeling project. Semi-dry screed is a good option for projects that need to be finished quickly because it dries faster than traditional methods. Its cement, sand, and water mixture necessitates careful application to produce a smooth finish, making it perfect for settings like homes or workplaces where efficiency and quality are crucial.

Regular floor screed is more versatile in application than semi-dry, but it takes longer to dry because it is usually made with a higher water content. This technique works well for larger spaces or projects where accurate leveling is essential. The increased water content facilitates easier application and flow, which is beneficial for intricately laid-out projects or those requiring exact leveling.

Dry floor screed is useful for projects requiring quick access or involving materials that are sensitive to moisture since it can be installed and dried quickly using materials like gypsum or calcium sulfate. Although this technique drastically cuts down on construction timeframes, it must be installed carefully to avoid uneven or cracked surfaces.

The decision between semi-dry, regular, or dry floor screed ultimately comes down to the particulars of the project, including the budget, schedule, and surrounding conditions. Speaking with an expert can help you decide which option is best for your particular needs and ensure that your flooring satisfies the standards for efficiency, durability, and beauty.

Video on the topic

Floor screed and floor slab, they have different tasks

Screed. Which one to choose? Comparison of options. Semi-dry screed – advantages and disadvantages.

Which screed to choose for a heated floor, wet or semi-dry?

Which screed to choose? Classic or semi-dry?

SEMI-DRY vs CLASSIC floor screed

What happened to the semi-dry screed after a month??!

All about semi-dry screed for heated floors

✅ Semi-dry floor screed. What 98% of people don"t know. [SashaBagot.ru]

What factor is most important for you when choosing materials for building a house??
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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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