According to TV commercials, dryness is the new standard of our life today. Therefore, it is not surprising that dryness is now thought of everywhere, even at the construction site. In this case, we are talking about the technology of prefabricated dry floors. It is known that flooring starts with a screed. Traditional screed is made of cement-sand or concrete mortar (this process is called wet). But there is also a dry technology – less familiar and not very widespread yet, but in comparison with the cement-sand technology it is more economically attractive. Recently, it is increasingly being introduced into construction practice. This flooring option is used both in the construction of new buildings and in the repair of old buildings. In general, the idea of backfill prefabricated floors has been known for a long time and was widely used in our mass housing construction 30-40 years ago. In recent years, prefabricated dry floors have received a new round of development thanks to the development of a complex system of materials from the companies KNAUF and OPTIROC.
The essence of a prefabricated floor with a dry screed is as follows. A fairly thick layer of dry backfill is applied to the floor slabs. From above it is covered with durable sheet material (dry screed). And already the finishing floor is laid on it. The number of layers and the materials used may vary depending on the characteristics of the floor and the requirements for its quality. A dry backfill floor can be laid not only on slab floors, but also on floors with logs (both stationary and adjustable).
Why are such floors attractive? Why do they turn to them again and again? The answer follows from their very name. The main thing is that during installation it is possible to avoid wet processes associated with concrete work. As a result, the labor intensity and duration of the construction cycle is reduced, it becomes possible to easily lay communication lines in the screed, to provide high heat-shielding properties of the floor, and sometimes the required sound insulation.
Such subfloors are preferred in the following cases:
The installation of floors with a dry screed is started after the completion of all sanitary, electrical and finishing works. Water and heating system tests must also be completed.
The device process can be described by the following points.
Floor surface preparation
Installation of a prefabricated floor begins with the preparation of the floor surface. First, the old floor (if any) is removed, the gaps between the floor slabs, the gaps between the floor slabs and the walls, installation recesses and potholes are sealed with a cement-sand mortar of a grade of at least 100-150, and the floor is thoroughly cleaned of construction debris.
Installation of a moisture-proof layer
The main problem with dry floors is the fear of moisture, and leaks are simply fatal for them. When installing a dry screed, it must be borne in mind that in the event of an emergency leak, the plates can swell, and then the front coating will deteriorate. That is why a vapor and moisture barrier is always laid under the base of the floor, on the ceiling. It protects the backfill located on it from moisture, which inevitably occurs when it comes into direct contact with the floor.
Why does moisture appear on the floor? There are two main reasons. First, vapors always come in from the room below. Secondly, moisture can be released from the concrete of the floor (due to excess water in the mixture or suction from the walls).
Using a hydraulic or laser level, mark the surface of the backfill on the wall and arrange its vapor and moisture protection from a polyethylene film. For this, the film is laid with an overlap of adjacent strips of at least 15-25 cm so that near the walls it rises to a dry screed. For vapor and moisture protection, ordinary polyethylene film with a thickness of 200-250 microns (in the case of a reinforced concrete floor), glassine or bituminized paper (for a wooden floor), as well as a more modern universal vapor barrier such as “Yutafol N”, “Svetofol”, etc. are most often used..
To exclude “sound bridges” and curvature of the clean floor from thermal expansion of the base along the walls along the entire perimeter of the floor, a gap of 8-10 mm is left. Sound insulation is placed in it – usually in the form of an edge band of mineral or glass wool of the M75 or M100 brand, polyethylene foam or other similar material.
Further, a loose material is applied, which serves to create a flat surface for the flooring, as well as to enhance the required level of thermal insulation and sound absorption. The backfill is placed on the film and leveled with a rail according to the marking level. For backfilling for prefabricated floors, materials are suitable that have an optimal granular composition, which ensures their minimum settlement, high porosity, good flowability, low hygroscopicity and mineral composition – for fire safety purposes. Screenings from expanded clay production, expanded perlite sand, quartz and silica sand, fine-grained slag and similar dry inorganic bulk materials can be used..
The thickness of the backfill depends on the quality (quantity and size of irregularities) of the floor slab surface, as well as on the presence and characteristics of utilities and other equipment. Typically, the layer thickness is 30-50 mm, but there are more. With a thickness of over 60 mm, the dry screed is reinforced with an additional layer of plates.
If the surface of the floor slab on which the base of the floor rests does not require leveling, instead of backfill, extruded polystyrene foam boards can be used tightly to each other. Also, expanded polystyrene plates are used in addition to the backfill to provide the required thermal protection and sound insulation, if they are not provided by the backfill itself. If it is expanded polystyrene, mineral wool or glass wool, they are carefully cut into small plates. When laying, it is necessary to ensure that the plates are very tight to each other. Again, they put edge tape along the walls..
Laying gypsum fiber sheets
If the insulation is backfilled, work begins from the door (so that during the work the builders do not walk back and forth on the just leveled surface). If they are insulation boards, workers will dance from the opposite wall..
It is possible to make a dry screed from moisture-resistant gypsum-fiber sheets (GVLV) of both regular size and reduced, from waterproof plywood, from chipboard (chipboard), tongue-and-groove chipboards with an oriented structure (OSB), asbestos-cement sheets. Recently, prefabricated floor elements made of two gypsum fiber sheets glued to each other and combined prefabricated elements with an additional polystyrene foam layer (“KNAUF”) have appeared on sale.
The stacking technology is determined by the type of sheets used. Floor elements made of moisture-resistant gypsum-fiber sheets glued together in the factory with displacement relative to each other in two directions, as well as chipboards, plywood and other sheet materials are laid, depending on the thickness, in one or two layers, firmly fastening them together during installation with glue and self-tapping screws. The seams from the fasteners are putty and polished. The screed surface is covered with bituminous waterproofing.
The illustrations below represent options for installing a dry floor..
Installation of a dry prefabricated floor using gypsum fiber sheets and dry backfill on a slab base.
The construction of a prefabricated dry floor, where a dry screed is laid on a layer of foam material – expanded polystyrene. Floor slab surface did not require leveling.
Grain composition, strength of granules, their moisture decisively affect the bearing capacity and settlement of the floor. Dust is not released during the filling process, and the room is easily cleaned of it .
Prefabricated dry floor of gypsum-fiber boards on a wooden base, laid on logs with a wax-impregnated paper gasket and carpet covering.
Floor plan with prefabricated slabs: 1 – base; 2 – lags; 3 – rough flooring; 4 – waterproofing; 5 – dry backfill; 6 – floor element; 7 – edging tape.
The dry prefabricated floor screed is ready. A floor with a foundation laid in this way can withstand the same loads as floors with a concrete screed. The base has an impact noise reduction index of 18-22 dB. With a dry screed, cable and film electric heaters can be used. A dry prefabricated floor with material and work costs about $ 10 / m2.