What is better: regular or semi-dry floor screed?

The proper type of screed is essential for preparing your floors for a new finish. The layer of material called floor screed is put on top of the structural floor to give the finished flooring a level, smooth surface. Regular screed, also called traditional or wet screed, and semi-dry screed are the two most popular varieties. Making an informed choice for your project can be aided by knowing how they differ from one another.

A mixture of cement, sand, and water is used to make regular screed, giving it a fluid consistency. After being poured onto the floor, this mixture is leveled and smoothed. It is renowned for being adaptable and for producing a surface that is incredibly smooth and level. Regular screed, on the other hand, may take longer to cure and dry, delaying the completion of your renovation.

Conversely, semi-dry screed requires less water in its mixture. As a result, the consistency becomes more crumbly and damp and compacts into place. Compared to ordinary screed, it can be simpler to work with and dries more quickly. If you’re on a tight schedule, this faster drying time can be a big help, but it takes more expertise to use properly.

There are benefits and possible disadvantages to both kinds of screed. The ideal option for your floor will depend on a number of variables, including the area’s size, the project’s timeline, and the particular needs for the finished flooring material. You can choose the option that best suits your needs and guarantees a sturdy, long-lasting foundation for your floors by contrasting regular and semi-dry screeds.

Aspect	Regular Floor Screed	Semi-Dry Floor Screed
Moisture Content	High, takes longer to dry	Low, dries faster
Installation Time	Slower due to higher water content	Faster, easier to handle
Strength	Good, suitable for heavy loads	Excellent, very strong and durable
Surface Finish	Smooth, often needs less finishing	May require additional smoothing
Cracking Risk	Higher due to more water	Lower due to less water

Features of the floor structure

When arranging floors, a screed serves multiple purposes:

1. preparation of the floor for the installation of a decorative surface layer;
2. creation of the desired slope, heat, sound and noise protection;
3. Protection of internal engineering systems.

Half -dry

This kind of hardware or mechanized screed is applied using a pneumonagneter, a specialized mortar pumping device, along with the addition of the fiber solution.

The following ingredients are combined in a semiautomated device mode: fiber, water, cement (M 500), and clean, washed sand. A plasticizer is added to fill it and arrange a warm floor made of water.

The resultant solution is fed into the filling zone under pressure in special hoses, and a specialized level—a laser level, as a rule—levels it. The screed surface should then be machine-ground as an additional step.

Since this kind of screed is a "floating type," metal beacons are not utilized, and the base beneath it is not primed. One of its benefits is that minor building deformations in this scenario will be dampened without causing harm to the floor’s overall structure.

Engineers created this technology to expedite the labor-intensive process needed to construct high-rise structures. Nevertheless, the method’s benefits quickly led to its application in low-rise housing, as semi-dry pouring with modification M 150-180 is thought to be the most consistent and long-lasting of all pouring techniques.

About the benefits and drawbacks of semi-dry screed, see the linked article.

Composition of mixtures

The process is based on the conventional wet screed method, which involves diluting a cement-sand mixture with water and pouring the resulting solution onto the floor. It is only through this method that significantly less water is needed to give the solution the required plasticity. It should simply roll into a lump that easily maintains its original shape rather than flowing.

Water almost entirely hydrates the cement molecules with this consistency, never evaporating from the surface that results. As a result, the screed dries quickly, allowing for walking on it in about 12 hours and the floor’s use for additional construction work after 4 days.

Coatings of moisture-sensitive materials, such as wood, parquet, and laminate, can only be applied after this time because the process of moisture evaporation will take at least another two weeks.

Plasticizers are added to the concrete solution to increase its fluidity during the high-speed drying process so that the strength of the floor is not diminished. In order to prevent surface cracking and subsidence, semi-dry screed fills in corners and the spaces between built-in communications while also forming a dense border with the walls.

Such a layer gains so much strength that it approaches reinforced concrete in certain aspects.

A detailed description of the mixtures can be found here.

Pros and cons

The high curing speed of the semi-dry pouring method is its primary benefit and the reason for its extensive use in construction. Furthermore, the following were installed during the pouring process and the finished floor’s subsequent operation: Benefits:

1. Low percentage of water in the solution, eliminating the formation of voids, uneven drying and low percentage of porosity of the layer.
2. There are no moisture leaks to the lower floors when pouring the screed.
3. Uniform distribution of loads on the floor, as a result of rapid hardening of the layer.
4. It tolerates high temperature differences well.
5. High performance in terms of heat and sound insulation of the layer.
6. It is possible to simultaneously lay 2 adjoining multi-level sections, without formwork.

The high cost of small objects; the requirement for precise execution of the technology of work, which necessitates the involvement of professionals in the work; and restrictions on the layer thickness, no more than 5 cm, due to the high density of the material in the solution creating an excessive load on the base are some of the drawbacks of this floor pouring technology.

The developer must prevent the solution from coming into contact with water and from being exposed to low temperatures during the installation process.

Standard wet concrete

Because of its high labor intensity and low labor productivity, "wet" floor screed is becoming less and less common in mass housing construction today. Usually, it is poured straight from a mixer onto the construction site via specialized hoses.

Initial steps include priming the base for wet pouring, setting the steel beacons, pouring the solution, and pulling out a layer along the beacons. The beacons are taken out of the solution after it has solidified. It will be necessary to use self-leveling mixtures in addition because the base comes out uneven and with significant differences of up to 3-7 cm due to the large amount of water.

Areas where concrete screed is used:

• correction of floor slope;
• uniform distribution of mechanical loads of the floor.
• increasing its strength characteristics to dynamic / static overloads.

Composition of mixtures

The grade strength of the wet screed needs to be at least M150 in order to comply with GOST and SNiP regulations. Its fundamental elements are:

It is advisable to purchase a ready-made dry mixture with the PCS M150 marking, though you can probably find one in a construction supply chain.

The strength of the screed will depend on whether you buy cement that is at least M200 or better, such as M400/500, for the autonomous production of a dry mixture.

Sand ought to pass through a sieve with a cell size of no more than 5 mm; it should also be devoid of many clay and sea sand-specific minerals. Any source of water should be pure; sea and salt water are also acceptable.

A plasticizer, lime, fiber, and clay can be added to the wet screed, depending on its intended use, to give it plasticity and resistance to frost. A certain brand’s requirements are taken into account when setting proportions.

The percentage ratio of "water – cement" should be between 28 and 30% in order to produce a screed of superior quality. If it is exceeded, numerous voids will form and the layer won’t get the necessary strength. It also becomes looser with less water, losing its strength and solidity.

Pros and cons

The primary benefit of this kind of flooring is that it is simple to install and doesn’t require highly skilled artisans. Furthermore, such a solution takes a long time to harden, giving unskilled workers plenty of time to slowly level its surface.

Fundamental benefits of a conventional concrete screed:

1. Universality, allows you to perform both connected and floating screed options.
2. Wide range of application – for residential and industrial construction.
3. A thick self-leveling layer, sufficient to cover built-in utilities.
4. Alignment of large height differences using reinforcement with iron meshes.
5. Use of ready-made mixtures or prepare them at the construction site.
6. Performing screed both manually and mechanically with the same quality.

The drawbacks of wet screed are attributed by experts and users to higher shrinkage, particularly in the center of the array, a higher susceptibility to cracks, high labor costs, and a lengthy drying time of 28 to 30 days.

24 hours after pouring, beacons are always taken out and any remaining cracks are sealed to ensure an even floor plane.

Comparison of the characteristics of two types

To ensure complete accuracy in this comparison, you must understand that, in the course of developing a construction project, the appropriate version of the screed is selected by means of a technical and financial comparison of two options.

Given the large number of technical and financial indicators involved, this is a fairly complex process. Both options are, in theory, very similar to the conventional technique of leveling a floor with a solution that uses cement and sand as the basic materials; the only differences are in the water levels and the degree of mechanization. In this instance, a human is in charge of these two processes.

Strength

This is the most fundamental metric for evaluating a screed because it describes the screed’s resistance to both static and dynamic loads.

Traditional wet is in the lead screed in this comparison, able to withstand loads of up to 20 MPa. With readings between 15 and 18.0 MPa, semi-dry screed performs better than dry screed but still falls short of wet screed.

The semi-dry version has a density of 1450 kg/m3, whereas the wet version has 1800 kg/m3. This can be explained by the difference in solution densities. In actual use, fiberglass and reinforced mesh can be used to slightly increase the strength.

Durability

The two kinds of screeds under comparison should, in theory, have about the same service life. It remains the same for roughly fifty to one hundred years when there are no harsh operating conditions.

Numerous variables that impact the longevity of both wet and semi-dry screeds are linked to such a wide spread, including:

1. Composition determined by the brand of concrete and cement and water resistance class. Technological proportion of components.
2. Fillers of the floor base, so expanded clay can last over 75 years, and arbolite less than 50 years.
3. Compliance with the pouring technology.
4. Operating conditions: impacts, vibration, moisture and temperature changes destroy even a very strong screed.

Resistance to temperature changes

This indicator shows that the semi-dry screed has an advantage because it uses reinforcing additives and requires less water. Initially, the wet modification does not require the application of different kinds of water repellents.

These additives also introduce tiny air bubbles into the concrete solution, which enhance the mass of the solution’s overall mobility and raise the composition’s quality in terms of resistance to temperature fluctuations and moisture.

Conclusion: Resistance to temperature changes is higher in semi-dry screed, due to the lower percentage of water in the solution.

Moisture resistance

This indicator suggests that a semi-dry screed is the best choice. This is explained by the characteristics of its fiber-using device, which hydrates cement with the least amount of water.

It is advised to use a ready-made dry mixture for small pouring volumes and to prepare the solution right before laying in line with the factory’s instructions.

It will be necessary to undertake numerous labor-intensive and costly measures, such as waterproofing and base insulation, in order for the wet screed to acquire the desired moisture resistance characteristics.

Thermal conductivity

Because there is a lot more water in the wet than in the semi-dry, the wet has a much higher thermal conductivity. Hence, the thermal conductivity index for wet materials is 0.6-0.9 W / m * K, while that for semi-dry materials is 0.45-0.46 W / m * K.

This implies that the second screed is warmer because it will conduct less heat. A minimum 5–6 cm layer of expanded clay must be laid, which will require additional labor-intensive and costly work, in order to achieve high resistance to wet screed.

On the other hand, there are situations where using wet screed is better than semi-dry. For instance, in an underfloor heating system, to transfer heat from the heating elements to the room.

In this version, the screed is made wet for more intense heat transfer to the room, and the base under the "warm floor" system is seriously thermally protected so that heat does not go into the ground.

Semi-dry screed is the best in terms of thermal conductivity, but installing a traditional wet screed is preferred in the "warm floor" system.

Loads on floors

This is a critical indicator, particularly for long-life weak floors. The traditional wet screed achieves a specific gravity of 1800 kg/m3, whereas the semi-dry one has a specific gravity of 1450 kg/m3.

However, since the thickness of the fill is crucial to take into account, this indicator is insufficient to accurately compare the two options. One square meter of semi-dry screed weighs 15 kg, while one square meter of wet screed weighs 20 kg.

The semi-dry screed places a much lighter load on the floors.

Level of complexity of the device

The degree of mechanization and the use of skilled labor determine the complexity of the work involved in pouring the floor. This means that the semi-dry screed, which requires the use of machinery and can only be executed by skilled builders, is the most complex method.

A home craftsman can manually apply a wet screed, which is preferable in terms of complexity.

Surface quality

It is decided by the coating’s appearance, which the standard describes as dry and smooth. The semi-dry screed has an advantage in this indicator. Because of the enormous amount of water in the solution, uneven shrinkage can occasionally cause a height difference of up to 7 cm when working with the "wet" method.

You will also need to invest in costly and labor-intensive pouring and grinding work to level the floor in order to obtain a smooth surface.

In conclusion, the semi-dry method yields a higher level of surface quality.

Required thickness

The technology used in floor construction and its intended use determine it.

When it comes to the lowest acceptable indicators, the semi-dry option allows for the smallest ones up to 5 cm, while the wet option allows for the smallest ones up to 10 cm and even higher, provided the floors can support the weight.

However, the minimum fill level is not always beneficial. For instance, this thickness is typically insufficient for the "water heated floor" system.

Semi-dry screeds are preferable in terms of the necessary thickness, with the exception of floors that are installed using the "warm floor" system.

Application areas and places

Semi-dry screed is thought to have the broadest range of applications; experts advise installing it in every room of both low-rise and multi-story buildings, including humid areas, those with significant temperature variations, and floors with weak support.

Only spaces with a weak base, like boiler rooms and garages, can benefit from the wet option.

Compatibility with underfloor heating

The "warm floor" system can be used with both approaches, although the wet method offers greater benefits in terms of layer thickness and thermal conductivity. Plasticity is the only area where it falls short of the semi-dry option, although plasticizers can be added to change this parameter.

When using underfloor heating, the wet pouring option is recommended.

How to combine with various finishing coatings?

When comparing two screed options, this indicator indicates that the semi-dry option is better because it involves achieving a perfectly flat top surface, which is necessary in order to use finishing coatings like:

1. parquet;
2. tile;
3. laminate;
4. carpet;
5. linoleum.

Large volumes of water in the solution cause uneven shrinkage, which causes noticeable differences when laying the floor using the wet method.

They prevent you from moving forward with finishing the job right away; instead, more costly and time-consuming steps must be taken to level the surface.

Average material costs

When selecting a method for getting the floor ready for the finishing coat, this is one of the key factors that is considered. Here, the wet method has an advantage because it uses more inexpensive ingredients—water and sand—in its composition. Consequently, average prices:

1. traditional concrete solution for pouring 1 m 2 of floor is 320 rubles.;
2. for semi-dry version – 400 rubles. and higher.

Prices for work per m2

A comparable benefit exists for semi-dry floor pouring:

• the average cost of pouring 1 m2 of floor using this method costs the developer from 250 rubles.;
• using the wet method – from 400 rubles.

The need to work with heavy and large volumes of solution and the absence of mechanization tools account for this discrepancy.

How to choose?

The choice is mostly influenced by the type of building, the materials used for the walls and ceiling, and the functional purpose of the space, such as whether it will be used as a bathroom, bathhouse, furnace room, or if a fireplace or stove will be present. The advantages of choosing one option over the other are not always evident.

For rooms with high humidity

This kind of property necessitates a unique approach when selecting the kind of screed so that it can operate for more than 50 years without causing problems for the property’s owners or their neighbors.

These items consist of:

• bathroom;
• toilet;
• shower;
• open balcony;
• basement;
• various utility rooms.

Additional benefits of semi-dry screed include its ease of production; wet screed will incur higher costs for reinforced waterproofing.

Private houses made of different building materials

Private homes with distinct wall and ceiling materials necessitate entirely different floor plan arrangements:

1. in houses with light wooden floors, the semi-dry option is definitely an advantage;
2. in typical panel or monolithic floor slabs, the wet option has an advantage.

Despite the fact that pouring a floor using concrete mortar the old-fashioned way takes longer to hydrate and costs more to level the outside surface.

This is because the floor slabs can support a heavier weight from the concrete layer, and this option can be completed on your own without the need for expensive equipment rentals or the involvement of qualified personnel. It can also be done at a minimal cost for materials.

Apartment

The semi-dry technique is unquestionably a more acceptable choice for preparing the floor for this kind of living space because it eliminates the need to create a thick layer, which is crucial in low-rise rooms of multi-story buildings. Furthermore, it eliminates the requirement for grinding and the application of a leveling layer. Additionally, the work is done almost entirely dirt-free.

The wet method will only be financially viable if work is done independently without the need to hire specialists.

Garage

The most preferred option in these kinds of spaces would be the conventional wet method using concrete mortar, where the goal is to create a high-strength coating that can withstand high static and dynamic loads rather than high external characteristics for the floor.

It can be completed independently due to the small volumes, so the cost of such a floor will be low in this scenario.

Useful video

Extra details in the video:

A regular or semi-dry floor screed should be chosen based on your unique requirements and situation. Both choices have benefits and may be the best one depending on the circumstances.

Conventional floor screed is a well-tried technique. Because of its strength and longevity, it is a dependable option for a variety of flooring projects. Nevertheless, it necessitates a more labor-intensive application process and a longer drying time, so it might not be the best choice for projects with limited time.

Conversely, semi-dry floor screed has an easier application process and a faster drying time. The project can be completed more quickly and with less mess using this method. It’s especially helpful in circumstances where time is of the essence. It might not, however, always offer the same level of durability and strength as a standard screed.

In the end, the optimal option will rely on the particular needs of your project. Take into account elements like the amount of time available, the desired durability, and the level of experience. You can make an informed choice that best meets your needs and guarantees a successful flooring project by weighing these factors.

Understanding the main distinctions and advantages between regular and semi-dry floor screeds is crucial when making this decision. Regular screeds are perfect for areas that need precise leveling because of their flexible application and smooth finish. On the other hand, semi-dry screeds provide a more durable option for high-traffic or load-bearing floors due to their accelerated drying time and increased strength. Weighing the benefits and drawbacks of each approach is essential before making a choice, as it will determine which is best for your particular project requirements, timeline, and financial constraints.

Video on the topic

WET or SEMI-DRY screed with underfloor heating? One opinion…..

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

Which screed to choose? Classic or semi-dry?

Floor screed Which is better? Cement screed. Floor screed. Mechanized screed. Self-leveling floor

Which screed to choose for underfloor heating, wet or semi-dry?

SEMI-DRY vs CLASSIC floor screed