All the nuances of the technology for installing a semi-dry floor screed

A semi-dry floor screed is a great option for building a level and long-lasting floor surface. Homeowners and builders alike prefer this technique because of its robust finish and short drying time. The semi-dry version of screeds is easier to handle and sets faster than traditional wet screeds because it uses less water. This method is perfect for both residential and commercial projects because it combines efficiency with practicality.

The first step in the semi-dry floor screed procedure is to prepare a dry sand and cement mixture. Next, a tiny bit of water—just enough to bind the ingredients together without becoming overly wet—is added to this mixture. The final consistency is comparable to damp sand, which is less likely to shrink and crack after it sets and is easier to work with.

The installation process entails completely compacting the mix after distributing it evenly over the floor area. To guarantee a stable, level surface that can tolerate heavy use, this step is essential. In order to achieve a smooth finish that is prepared for the final floor covering, such as tiles, wood, or carpet, specialized tools like power floats and screeding bars are used.

The quick drying time of semi-dry floor screed is one of its main benefits. When compared to conventional methods, floors can be fully cured in a few days and walked on within hours, greatly decreasing downtime. This makes it a well-liked option for tasks with constrained time constraints or when prompt access to the location is crucial.

Even with all of its advantages, a semi-dry floor screed takes skill and accuracy to get just right. Achieving the ideal blend and application are crucial to preventing problems later on. When executed correctly, a semi-dry screed offers a durable, superior foundation for any type of flooring, fusing durability and dependability with the ease of a quicker installation process.

Step	Description
Preparation	Clean the surface and apply a primer.
Mixing	Combine sand, cement, and water to achieve a semi-dry consistency.
Application	Spread and level the mixture on the floor.
Compaction	Compact the mixture using a special machine.
Smoothing	Finish the surface with a trowel for a smooth finish.
Drying	Allow the screed to dry completely before use.

A semi-dry floor screed installation combines the advantages of conventional wet screeds with quicker drying times and simpler handling to provide a level and long-lasting flooring surface. With this technique, cement and sand are combined with a small amount of water to create a wet, sand-like consistency that is then spread out and compacted on the floor. Reduced shrinkage and cracking, faster walk-on times, and the capacity to cover large areas more quickly are among the main benefits. Comprehending the particular procedures and optimal methodologies for this installation process guarantees a seamless, superior finish that amplifies the durability and functionality of the finished floor covering.

Necessary building materials

The biggest challenge with semi-dry screeding is that the density of the concrete makes it impossible to mix a workable mixture with a standard drill and mixer attachment. It will be necessary for you to buy the equipment already assembled, which can cost more than a million rubles.

As a result, most developers, particularly for smaller projects up to 200 m2, rent equipment. The daily cost of this equipment is determined by its configuration and can range from 2,000 to 10,000 rubles for the client.

List of building supplies, machinery, and tools required to produce PSP:

• a hammer drill, if it is necessary to remove the old screed beforehand;
• a shovel for filling the concrete mixture into a container;
• a pneumatic pump – for pressurizing and transporting the working mixture through concrete hoses, equipped with a 250 l mixer barrel, a compressor, most often placed on a chassis with wheels;
• a damper for soft and rhythmic feeding of a semi-dry mixture (PS) from a concrete feeder;
• a highly specialized grinding machine with a disc diameter of over 600 mm, after its use the floor surface is almost flat, the level gap in height on it is no more than 2 mm per linear meter;
• laser level;
• concrete hose with D= 65/80 mm;
• air compressor, supplying air to the pneumatic pump;
• concrete shoes with a shape similar to fins, so as not to spoil the base of the screed when walking;
• rule for pressing and leveling the working solution along the beacons;
• vibrating screed;
• trowel / float for eliminating minor defects;
• cement M 400/500;
• clean sand, prepared by washing, 1st category, module 2.5-3.0;
• polypropylene fiber 12 mm for reinforcing the mixture;
• plasticizers, to impart plasticity to the solution and fill the voids under utilities, if the project provides for their installation in the floor;
• insulating roll material Penoterm;
• polyethylene film not lower than 100 microns;
• damper tape, foamed polyethylene, 4 mm, for sealing the joints between the walls and the floor, ensuring the creation of a movable "floating screed", and the subsequent free movement of the structure during the natural expansion process;
• beacons from T-shaped metal profile.

Stages of mechanized type arrangement

A series of steps in this process include the following necessary actions:

• implementation of general preparatory work: dismantling of the previous coating, sealing of large defects – potholes, large cracks and removal of garbage;
• preparatory work for PSP: dust removal, surface cleaning, priming to ensure adhesion, laying of insulating materials: moisture, heat and sound protection;
• installation of a damper tape along the general perimeter of the room, in order to form an expansion joint to neutralize possible deformations of a natural nature during expansion/contraction of the floor structure;
• marking the floor in cleanliness and "0" level;
• installation of beacons;
• preparation of the working mixture and its supply by a pneumatic pump to the working area;
• spreading the mixture over the general surface with tamping by a vibrating screed;
• performing final processing with compaction operations, eliminating voids and grinding, using a disc grinder;
• execution of shrinkage joints according to the design scheme.

The construction project may specify further work, such as installing heat transfer systems in the "warm floor" structure or strengthening reinforcement with mesh.

Step-by-step instructions for pouring

When semi-dry screeding is done quickly, the resulting layer has high strength characteristics and is extremely smooth, in contrast to traditional "wet" laying. However, this outcome will only be attained if the performer adheres closely to the technology.

It is extremely difficult, requires specialized tools, and can only be completed by individuals with construction experience and the know-how to safely operate pricey, complicated machinery.

It is preferable to enlist the assistance of an experienced specialist when a home craftsman lacks the necessary experience. Depending on the type of execution, there are different step-by-step instructions for doing PSP by hand. The three most useful varieties at the moment are the basic version without a substrate, the screed with heat protection, and the screed with noise insulation.

Generally speaking, layers of moisture and vapor protection, mechanical damage resistance, and heat and noise absorption are required for mineral or basalt wool.

The installation technology determines how long it takes to lay PSP. If the base is in good condition and only needs small amounts of restoration work, the maximum shift rate of work when mixing the solution by hand is 50 m2.If the base is covered in cracks and needs extensive restoration, the maximum shift rate of work is 35 m2. The daily rate for a team of four when using a mechanical supply of solution is 300 m2 of coverage.

Preparation of the base

This is a critical step, and the quality of its execution will determine how strong the entire future floor structure is. Failure to do this will probably result in the future screed developing cracks all over it, peeling off from the base, or surface tears.

Standard procedures for setting up an apartment’s base:

1. Most often, the base for the screed in an apartment is a concrete floor slab, which must be carefully examined for defects.
2. Sweep out the debris and assess the condition of the slab.
3. Detected cracks and inter-tile gaps are carefully sealed with cement-reinforced concrete.
4. After the solution has hardened, remove all unnecessary materials with an iron brush and clean the surface, it is advisable to sweep it and even vacuum it.

How waterproofing is done?

Semi-dry screed should never be attached directly to the base because the PSP’s moisture will quickly seep into the concrete slab, causing the layer to crumble and lose its strength. Instead, place a polyethylene film on a clean base to keep the concrete screed from drying out too quickly and from becoming dehydrated.

This prevents any water leaks to the lower floors and helps to maintain moisture in the screed mortar for the duration of the cement crystallization process.

The film cannot perform the functions of waterproofing. If, according to the project, waterproofing should be arranged before the semi-dry screed, it is carried out independently of the film, in this case, first the entire protective pie is arranged:

• water protection;
• thermal protection;
• vapor protection;
• film under the screed.

More than ten centimeters of overlap are covered with waterproofing, which is installed with sealed seams and five centimeters above the semi-dry screed’s intended level. After that, a damper tape is put in place to keep the screed and walls apart. You can create your own custom tape using PPE/PUF or purchase one from the retail network.

The first choice is better because the product is ready to use and has already been treated with an adhesive composition. The level is 5 cm above the screed’s upper cut, and it is adhered with an overlap. The extra damper tape needs to be cut off once the semi-dry screed dries fully.

Installing beacons

Mark the "horizon line" on the walls with a laser level before attaching beacons. Its optimum height is 30 cm, and its maximum height is 1 m. Place the level in the center and point the beam in different directions toward each wall. Verifying the accuracy of the work: the "horizon lines" used to indicate the corners should come to an end.

When setting up PSP in multiple rooms, guide the beam through the open doors to identify the subsequent "horizon line"; then, proceed to the next room and so on across the apartment.

Next, identify the "zero level" by measuring the shortest distance to the concrete slab; this measurement will serve as a shared indicator for the whole apartment. Next, draw the desired line parallel to the "horizon line" at the point where the screed should be poured, retreating from the "zero" by its thickness. It has benchmarks placed along it, and a rule will be used to level the screed surface along those benchmarks.

To create the monolithicity of the semi-dry screed, the PSP is laid simultaneously with the beacons being pulled.

It is necessary to use a laser or another more precise level to verify the level at which the beacons are set. The beacons are positioned throughout the floor base, with a spacing between each that is shorter than the rule’s length. As a result, the plane will be able to level itself between two beacons in a single pass, guaranteeing a level surface throughout.

How to fill using pneumatic-mechanical equipment?

Pneumatic pumps and grinding machines are used in this option, which lowers labor costs for builders while improving output quality and speed. Professional equipment is utilized for these purposes in large industrial volumes; the most well-liked facilities are those owned by the following companies:

1. BMS;
2. Putzmeister;
3. Hilti;
4. Brinkmann.

Teams of three to four skilled builders maintain this equipment, ensuring uninterrupted pouring operations.

The process is very straightforward and uses concrete hoses in conjunction with pneumatic pumps:

• A well-mixed solution is fed to the desired height, a possible indicator of up to 120 m, and horizontally up to 200 m, the specific length of the feed is determined by the length of the concrete hose.
• One person from the team operates the pneumatic pump, the rest are involved in receiving and evenly distributing the solution over the entire area. After the solution is completely poured into the room, they begin to level it using a laser level and a rule, with a recommended length from 0.5 m to 3 m.
• Mechanized grinding is performed using a special machine with a grinding wheel diameter of 60 cm, work begins in 10-15 minutes., after leveling the semi-dry solution. On corner and joint areas, it will be necessary to use a grinder with a smaller nozzle diameter than the pneumatic pump.

Performers are required to wear special devices on their feet, concrete steps, to prevent them from squeezing through the "fresh" concrete mortar.

Once the work is finished, a film is applied to the entire floor area and allowed to dry. Time spent hanging semi-dry screed:

• 12-18 hours you can walk on the screed;
• 24 hours in the absence of drafts you can start finishing the walls;
• 1-2 days – installation of porcelain stoneware or tiles;
• 5 days the screed can withstand a weight of up to 100 kg;
• 7 days – linoleum is laid;
• 10 days – scaffolding and other heavy equipment are allowed to be installed on the PSP;
• 28 days – work is carried out on the finishing coating with materials that are sensitive to excess moisture, for example, laminate.

Features of the process for buildings

Both residential and non-residential buildings’ concrete floors must adhere to state regulations, be strong, ergonomic, and not produce dust. They must also support the calculated loads, though the amounts of loads for each can vary significantly.

Non-residential premises typically consist of:

1. furnace rooms;
2. garages;
3. commercial and industrial buildings.

They are all more resistant to mechanical and chemical stresses that could otherwise destroy the screed.

Furthermore, there are differences in the external finishing coating used in rooms designated for this purpose. Open concrete floors without a finishing coating are prohibited in residential buildings due to stricter sanitary regulations, but they are permitted in non-residential buildings.

In this instance, further hardening compound treatment will be necessary to stop dust from forming and strengthen the surface layer’s resistance to impact.

In addition to being harmful to human health, cement dust causes equipment and appliances to malfunction by getting into critical components and electrical boards.

The floor plans of residential and non-residential rooms differ from one another in the following ways:

• In the thickness of the screed layer: for residential up to 40 mm, for non-residential with high impact load up to 60 mm.
• The presence of a finishing coat: for residential – mandatory, for non-residential – a concrete coating without a finishing layer can remain.

Furthermore, in residential settings, reinforcing mesh is not necessary; however, in non-residential settings, the choice to install a reinforcing layer is typically based on the weight of the equipment and mechanical loads.

Residential premises

As per current regulations, in order to execute a semi-dry screed for residential properties, the fundamental PSP technology involving plasticizers and fiber will need to be carried out. The purpose of the latter, which is composed of 12 mm polypropylene, is to provide trustworthy reinforcement.

Materials required for a living area of 100 m 2 with a 40 mm screed thickness:

• the norm of the ready-mix for 1 m3 of M-200 grade mortar, for M400/500 cement will be 350/250 kg, respectively;
• to create a screed, the required volume of solution is: 100×0.04=4 m3;
• for this, you will need cement M500:250×4=1000 kg, 20 bags;
• sand consumption during shrinkage 1.15:1.15×4=4.6 m3;
• water consumption at the rate of 120 l per 1 m3 of semi-dry mixture: 120lx4=480 l;
• fiber consumption at the rate of 0.7 kg per 1 m 3 will require: 0.7 x 4 = 3.2 kg.

Non-residential

In order to create a durable concrete base and strengthen the outer surface with topping, it will also be necessary to purchase reinforcing mesh for such floors because semi-dry screed is made in non-residential premises in a single technological cycle.

As a garnish, also utilized:

• quartz, creates resistance to mechanical loads, recommended for retail and warehouse premises, basements, boiler rooms and garages;
• cutting shrinkage joints and filling them with sealants in order to eliminate all kinds of deformations.

The cost of materials for installing a floor with an area of 100 m2 and a layer of 60 mm will be higher in non-residential premises with increased impact load because the PSP layer thickness is significantly higher there than in residential buildings:

• to create a screed you will need a volume of solution: 100×0.06 = 6 m 3 ;
• for this you will need M500 cement: 250×6=1500 kg, 30 bags;
• sand consumption during shrinkage 1.15: 1.15×6 = 6.9 m 3;
• water consumption at the rate of 120 l per 1 m 3 of semi-dry mixture: 120 lx6 = 720 l;
• fiber consumption at the rate of 1.0 kg per 1 m 3 will be required: 1x 6 = 6 kg;
• reinforced mesh with a reserve of 1.1×100 m 2 =110 m 2 .

Installation difficulties and errors

A semi-dry floor screed is a labor-intensive and responsible construction process that calls for the precise execution of a technological map developed by the work’s manufacturer in accordance with the design solution for the floor’s manufacture, as well as the use of sophisticated pneumatic equipment.

The majority of the time, contractors make mistakes even before work begins. These mistakes include selecting the wrong multi-layer flooring technology, the kinds and orders in which to lay protective layers, the amount of semi-dry mixture, and the screed thickness. All of this causes the floor’s strength properties to drastically decline, and occasionally it causes the layers to delaminate.

The following errors are most frequently made when producing work for the PSP installation:

• the base is poorly prepared for pouring the screed;
• the film is not laid and waterproofing is not done or it is done with poor-quality joining of the strips;
• work on laying noise and heat-protective layers is not done;
• the "horizon line" is not set by a laser level;
• Beacons are not installed and damper tape is not laid.

Pros and cons of self-installation

PSP’s greatest benefit is thought to be its high productivity and low labor intensity. Experts also point out the following benefits of this kind of screed:

• low water content, does not create voids, the screed hardens more evenly, without forming a porous surface;
• no threat of water leakage to the lower floor;
• highest speed of solution hardening;
• high mechanical, impact and chemical resistance;
• no dust;
• high heat and noise protection rates;
• can simultaneously fill 2 different-level sections;
• no additional floor leveling required;
• minimal risk of cracking;
• reduced labor intensity due to the possibility of feeding the solution with a pneumatic pump to a height of up to 30 floors.

The drawbacks consist of:

• strict standards for layer thickness of 4-6 cm;
• the cost of work for residential properties is higher than for industrial ones, due to small volumes and expensive equipment rental;
• requires a high level of personnel training.

Useful video

Visual details of the gadget shown in the video:

A semi-dry floor screed requires careful planning, accurate execution, and the appropriate supplies. This technique is a favorite among builders and homeowners because it offers a steady and long-lasting base for a variety of flooring choices. It has many benefits, including better insulation and faster drying times, but getting the most out of the process requires knowing how it works.

Appropriate surface preparation ensures a clean and level base at the start of the process. The sand, cement, and very little water combine to form a wet paste that is then spread out and compacted. Maintaining the proper thickness throughout the area is essential for the screed to perform as intended, and using a laser level makes this easier.

The screed needs enough time to cure after it is laid. It dries more quickly than conventional techniques, but patience is still needed to prevent any possible cracks or weaknesses. Sustaining ideal moisture levels and shielding the surface from adverse weather conditions are crucial measures to guarantee the surface’s longevity during this time.

To sum up, learning how to install semi-dry floor screed can greatly improve the caliber and lifespan of your flooring. You can achieve a smooth and sturdy floor base by paying attention to details and following the specified steps. This approach is notable for its efficacy and efficiency whether it is used for business or residential projects.

Video on the topic

All about semi-dry floor screed, Floor screed, technological process

Device of semi-dry floor screed with fiber. All stages