When carrying out finishing work in modern construction, three basic types of screeds are used to level the base for the finish: wet, dry and semi-dry.
Wet screed call the traditional leveling of the floor surface with cement-sand mortar. After drying the fill and gaining 30% strength, the screed is sanded, eliminating noticeable imperfections. Due to the large volume of water in the mixture, wet screeds give significant shrinkage. In addition, the final set of strength of such a material occurs within 28 days, which makes it impossible to carry out subsequent work on these areas.
Dry screed It is carried out by filling the dry material with a small fraction, for which expanded clay is usually used. After leveling, special gypsum boards are laid on the screed, which are the basis for finishing. The disadvantages of this method include a significant change in the volume of the room, since the minimum height of the dry screed without coating is 50 mm.
Main advantages semi-dry screeds it is possible to finish the flooring shortly after preparation of the base, as well as strength comparable in performance to a traditional, wet screed.
The use of a semi-dry screed is recommended for the subsequent installation of any type of coating:
- linoleum,
- ceramic tile,
- laminate,
- parquet board
- traditional floorboard.
To obtain a working mixture use: quarry sand, fine fraction, sifted through a special sieve; cement grade M 500; water; plasticizers and reinforcing fiber.
Manual preparation of a high-quality mixture will not work. To ensure maximum adhesion of the ingredients with a minimum amount of water, a mechanical method should be used using a concrete mixer.
The peculiarity of the preparation of the mixture is the exact observance of the amount of each component in the solution. First of all, this concerns the amount of water: with a decrease in the volume of water, a sufficient set of strength will not occur and the screed will be loose, and exceeding the volume of water will crack the surface of the base.
The quality of the mixture is checked in this way:
- from a solution it is necessary to mold a “bun”;
- if it does not lose its shape and at the same time it does not feel high humidity - the solution is prepared correctly;
- if the "bun" crumbles or a significant amount of water is found in it - the solution is prepared with violations.
Semi-dry screeds are laid both on a monolithic base (rigid screed) and on a heater made of polystyrene foam plates or mineral materials (floating screed).
More and more masters, appreciating the advantages of this method of preparing the base for final finishing, recommend customers a semi-dry floor screed. The pros and cons of organizing such a foundation for finishing should be considered separately.
Benefits
The preparation of the base for finishing in the considered way has a number of positive aspects:
- This method is used both in new buildings and in old buildings;
- In the process, a minimal amount of dirt and dust is formed;
- As a result of high-quality laying and grouting of the surface, an ideal base is obtained, which does not require additional leveling with other mixtures;
- If reinforcing fiber is added to the mixture, it becomes possible to arrange a screed of small thickness, which leads to significant material savings and a reduction in the load on the floor slabs;
- Semi-dry mixture can be used to level the foundations in houses with wooden floors and floors, on concrete surfaces or on compacted areas made of bulk materials (sand, gravel);
- If it is necessary to obtain higher strength characteristics of the screed, reinforcement is used, for which a metal mesh is laid, interconnected by a wire and fiber is added to the solution;
- A qualitatively aligned semi-dry screed allows you to get an ideal base with minimal (1-2 mm) height differences, which makes it possible to start laying the laminate that is sensitive to differences without additional preparation, only by laying a substrate 3-4 mm thick. Also, such a surface is ready for the installation of ceramic tiles or parquet;
- When using mechanical means of supplying mortar, it is possible to carry out work in high-rise (up to 25 floors) buildings. The mechanization of supply also allows you to speed up the process of performing work;
- The height of the screed allows you to use this base when laying floor heating. Inside the screed, communications for the equipment of underfloor heating (pipes or cable) are freely located;
- To perform the work does not require a special temperature regime, you can arrange a screed at values from -5 to +40oC, while air humidity does not affect the process of building strength of the base;
- The peculiarity of the preparation of the mixture can significantly save water, a certain amount of which is necessary only for the process of hydration of the mixture, respectively, there is no risk of flooding the lower floor;
- Pre-installed waterproofing of the floor surface also allows you to insure against leaks;
- The setting time of the solution is 12 hours. After this time, you can move around the surface and begin preparatory work on finishing, and after three days you can lay the finish coating. In the case of pouring a wet screed, would have to wait at least 28 days;
- The screed device provides additional heat and sound insulation;
- Semi-dry mixture can be laid in rooms with a complex configuration, as well as in places with an angle of inclination of up to 30 degrees;
- Semi-dry mixtures can be used not only to prepare for the final finishing of the floor, but also to organize the basis for roofing;
- All the ingredients used to prepare the solution are environmentally friendly, not allergens and not harmful to human and domestic animals;
- Low cost;
- The small volume of water used to prepare the mixture allows to achieve minimal shrinkage of the material when it gains strength.
Disadvantages
The undoubted advantages allow in most cases to decide on the installation of semi-dry floor screed in residential and administrative buildings. The disadvantages of this method of preparing the base for further finishing are not significant and most often the occurrence of problems is associated with low qualifications of the contractors.
Cons of semi-dry screed:
- The inability to prepare a high-quality solution manually. The technology for preparing the mixture involves thorough mixing of the ingredients, which can only be done in a mechanical device;
- The loose mixture does not always allow you to accurately determine the required volume of the solution to obtain the desired height of the base;
- Violation of the exact volume of water required to form a high-quality mixture leads to a change in the technical characteristics of concrete. Excess water causes cracks, and a deficiency will not allow you to effectively complete the setting process of the solution;
- It should be remembered that the minimum height of the screed performed by this method is 40 mm, and for floors with insulation - 50 mm. The arrangement of such a foundation in old prefabricated houses with low ceilings leads to a significant reduction in the volume of living space;
- If a poor-quality surface grout is made, especially in rooms with a complex configuration, partial destruction of the base is observed over time, cracks and chips appear, which causes damage to the finish coating;
- To obtain a good foundation requires the involvement of experienced craftsmen;
- Only fine-grained sand is used as a filler in the mixture, which requires additional costs for sifting this material;
- Often there are problems when trying to tighten the screed in hard to reach places, which leads to a loss of pace of work;
- The process technology implies the continuity of the laying of the material on the surface and its compaction. It is impossible to complete such work alone, therefore, the involvement of a whole team of finishers is required;
- To raise the finished mixture to high floors will require the involvement of special mechanisms, which increases the cost of work.
The disadvantages of a semi-dry floor screed usually do not appear if the technology is not disturbed during the work process. Accuracy is especially important when preparing the mixture, therefore it is best to involve experienced specialists to carry out work on organizing such a foundation.