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COMPACT SUBSTRATES ENSURE THE STABILITY OF THE FINAL CONSTRUCTION AND IMPROVE THE CHARACTERISTICS OF FLOORS

In addition to the excellent aesthetic result, the floors must meet a number of mechanical and functional criteria. Although characterized by their topcoat, floors are made up of overlapping layers that make up a complete structure. The base is understood as the support base of the floor (usually a load-bearing slab of reinforced concrete), while the substrate is the layers that are inserted between the base and the final coating and are intended to provide or strengthen the various properties (e.g. water vapor barrier, sound insulation layer, etc. .a.). The substrate of a floor is applied to a load-bearing structure, which is usually a reinforced concrete slab. Depending on the particular requirements and the nature and condition of the substrate, suitable substrates may be inserted. The same substrates find applications in a variety of floors, while many coating materials have built-in substrates, which cover the usual requirements.

Substrate selection and preparation
For the successful selection of the substrate type the following should be taken into account:
• The use of application space.
• The coating material, so that the substrate is not weaker than the coating and its surface is compatible with the coating application materials (glues, mortars, floating floor substrates, etc.).
• Other additional operational requirements (thermal insulation, reduction of airborne and impact sounds, waterproofing).
• Other factors, such as weight, cost, ease of application and replacement, etc.
Indoors, as an intermediate leveling layer to ensure a stable, flat, smooth and even surface, on which the final coating will be applied, solid substrates of unreinforced or lightly reinforced concrete are used, as well as lightweight aggregates.
During the construction of the substrate, special attention must be paid to the formation of joints, where required, as well as to the continuation of the existing joints of the substrate. Cement mortar substrates up to 3 cm thick include special chemical additives. The required layer thickness determines the number of overlapping layers applied. An increase in the density of the down fabrics implies an increase in sound reduction and thermal conductivity.
The concrete surface can accept almost any type of coating. Surface preparation varies in combination with the coating material. Solid materials such as ceramic tiles, stone or brick, as well as laminated wood or resilient materials such as carpet, vinyl, etc., can be applied directly to the concrete. The installation of a waterproofing layer is deemed necessary on floors that are based on natural soil, on floors that are above wet areas (e.g. bathrooms), on floors with underfloor heating and on lightweight concrete floors.

Construction materials
Anhydrides (mixtures based on calcium sulfate)
They are gypsum mortars, in which the hydration of calcium sulfate (anhydride) leads to solidification. As with all gypsum products, their shrinkage rate is low, so they can be laid over large surfaces without the need for joints. However, as they generally take a long time to dry, it is not recommended that they be very thick. Also, as gypsum products they are vulnerable to moisture, so they should not be used on exterior floors and are not recommended in areas with high humidity.

Magnesite
They are known as magnesite cements and often contain quartz sand, they provide great strength and for this reason they are used in industrial areas, as well as in other areas of heavy professional use. In the past, wood shavings were used instead of quartz sand, while today this method of construction in a thin layer is only used in residential renovations. They do not develop large shrinkage deformations, so they can be laid on large surfaces without joints and provide great resistance to wear. Any metal elements in contact with the floor should have a protective coating, as there is a risk of electrochemical corrosion. They are also not recommended in areas with permanently high levels of humidity.

Synthetic resins
They are mixtures of various resins (epoxy, polyurethane, methacrylate, etc.) with quartz sand or other inorganic granular materials and, depending on their composition, provide different properties to the subfloor. The advantages of these products are rapid curing, which allows the rapid coating of several layers. They provide a uniform appearance, smooth surface and good durability. Their surface is not particularly resistant to surface damage, they discolor over time, while under conditions of high temperatures and/or humidity they tend to create swellings on their surface due to osmotic action between the resins and the concrete, which constitutes the load-bearing infrastructure.

Cementitious mixtures
They are mixtures of Portland cement, aggregates and water, while the incorporation of additives into the mixture gives different properties to the final product. Used in a multitude of applications, they are non-combustible and durable, like all cement products. Their drying favors the creation of microcracks, to prevent which joints should be formed or additives used or the ratio of water to cement (as small as possible) or the quantity of aggregates in the mix (as large as possible) should be adjusted appropriately. Usually, to reduce the dead loads, the floor coverings are used for floor coverings, which have a lower density than concrete and at the same time provide thermal insulation and sound insulation protection, which may be desirable in some cases of floors. Admixtures with slightly porous aggregates, natural or artificial (kisiri, perlite, etc.) or with air pockets in their mass, are usually used.

Lightweight aggregates with porous aggregates
Laying and compacting the light aggregate with porous aggregates is easier compared to ordinary concrete. The density of these down bales ranges from 300 to 2,000 kg/m3 and their strength between 0.3 and 40 MPa. Their resistance to surface wear is moderate, while its behavior in fire is improved in relation to the behavior of ordinary concrete due to the lower coefficient of thermal conductivity.

Lightweight packages with air pockets in their mass
Mortars of this type are prepared without coarse aggregates and in some cases without aggregates at all. In any case, the maximum aggregate grain size should not be greater than 1/3 of the minimum layer thickness. Thus, they have a very low density (200 – 400 kg/m3) and consequently low strength, so they are generally used as thermal insulation layers. To deal with the appearance of cracks, fiber reinforcement can be placed. They present very good workability, which allows the material to be easily laid in layers of small thickness without compaction, which, however, decreases with the increase in the amount of aggregates.
Both types of the above downfills due to their increased porosity are vulnerable to moisture and for this reason they should be protected with a suitable sealing layer, while the use of mass sealants is not recommended, as it can adversely affect the quality of the final product . They are applied to floors with moderate or light use (homes, offices, leisure areas, shopping centers, etc.). Laying them on floors above the ground does not offer a particular benefit, as the main reason for their installation, which is their light weight, does not apply in this case, while the thermal and sound insulation properties they offer can be achieved with other materials easier to use and at lower cost.

Precast slabs
Solid slabs of various materials can also be used as the substructure of the floor, such as fibre-reinforced gypsum slabs in two or three layers depending on the area of ​​application (residential or public gathering areas). Plates made of wood products are also used to protect any heat-insulating layers or for the floating configuration of the floor. Both of the above types of slabs must be protected from moisture, usually with polyethylene sheeting over the load-bearing substructure, in order to prevent moisture from transferring to the slabs. Finally, pumice boards with glass fiber reinforcement are used.

Construction of joints
In concrete sub-floors the development of shrinkage cracking cannot be completely prevented, but it can be limited and concentrated in predetermined areas. For this reason, joints are made, while it is pointed out that the expansion joints of the building should also continue until the final coating.

Expansion joints
They are made to dampen the systolic and diastolic movements between parts of the construction. Their position is determined by the study and they are formed during the concreting phase. They are usually built around the perimeter of the flooring surfaces and in contact with vertical surfaces. Joints can also be shaped for sound protection reasons. They must be continued until the final coating.

Construction joints
Construction joints are formed where, for practical reasons, concreting stops and their position must be determined during the design phase. The reinforcement is not interrupted at the joint.

Control joints
They are formed as grooves in the floor surface and at a depth equal to half the thickness of the slab and are used to concentrate the cracks, which will develop anyway during the hardening of the concrete in a certain area and prevent them from developing in an enlarged zone. Their position is determined during the study phase. They are made in narrow areas of the floor (e.g. under doors, in changes of geometry (L shape) and in hemp per 20 – 25 m2 with lengths no longer than 5 m. They can be formed either over the entire thickness of the concrete (full joint), in which case they are formed during the concreting phase by incorporating a side formwork or plastic mold, or in part of it (control joint, false joint). The formation of false joints acts as a relief for the concrete, as it concentrates the cracks in the concrete. The latter are divided into partial contraction joints, in which 50% of the reinforcement is interrupted, and full contraction joints, in which all the reinforcement is interrupted. Beams can be used to transfer shear forces.

Source: https://www.ktirio.gr/