Thin-layer leveling compounds, self-leveling mixtures, different types of screeds – we are talking about different materials for leveling the floor and how to install them.
The base of the floor in an apartment is rarely perfectly flat, because usually the floor is assembled from individual reinforced concrete slabs, at the joints of which there are level differences, and some of the elements can be laid with a slope. The consequences of careless or improper preparation of the subfloor can be obvious immediately after the renovation is completed: it is difficult not to notice the bulging floorboard or sill on the border of the rooms. But much more often they make themselves felt later, when squeaks appear, as well as abrasions and cracks in the place of minor irregularities. How do you create a smooth and solid “base” for your flooring ? Let’s talk about ways to level the floor.
Putty for concrete
In many apartments (mainly in new houses), floor slabs are laid quite evenly, and their joints are reliably sealed; as a rule, a cement-sand screed is arranged on top. In this case, defects may remain. The elimination method depends on their nature, as well as on the type of flooring chosen.
Local overflows of mortar on the screed from the developer can be cut down with a chisel, and small pits and traces of the rule can be removed with a cement-polymer or polymer putty on concrete and thus a ready-made base for laying tiles, laminate or parquet boards is obtained. , since the slightest defects appear on them (finishing leveling with a bulk mixture is necessary). If, however, a solid board, adhesive parquet board or block parquet is chosen as the coating, it is necessary to ensure the high tear strength of the putty. A two-component epoxy putty is perfect for this purpose, but you need to carefully prepare the base – dust it, degrease it, and sometimes prime it with a hardening primer.
If there is a ledge, hill or slope on the screed made by the developer or the previous owners of the apartment, but the magnitude of the difference does not exceed 20 mm, for leveling it is advisable to use bulk mortars from ready-made mixtures. They are easy to apply, that is, in fact, they spread themselves over the surface – you just need to help them a little with a spatula and expel the air with a needle roller. Such solutions dry very quickly, and after 4-12 hours the base can take a foot load, and after 1-3 weeks (depending on the layer thickness) it is allowed to lay the coating.
Self-leveling mixtures can be combined with any coatings, but are quite expensive and, as a rule, can only be applied in a thin layer – no more than 30 mm. Read the instructions for use of the mixture carefully! Many materials of this type have specific requirements for the base, for example, they need to be dedusted, but exclude the application of adhesion primers such as concrete-contact.
Before pouring wet screed it is required to reliably waterproof the overlap with the entrance to the walls, otherwise the water from the solution will flow into the voids of the building structures (this can cause the wiring to close within two floors) and into the room below. In addition, when installing the screed, it is necessary to ensure the isolation of impact and structure-borne noise. Roll materials on a bitumen basis with a thickness of more than 4 mm or special two-layer substrates, will help to accomplish both tasks at once. All joints of strips (slabs) of waterproofing are glued with mastic or special tape.
Its optimum average thickness is 40 mm, the minimum local thickness is 20 mm. It is advisable to reinforce the structure with a steel road mesh, and prepare concrete from a factory mix in bags. With an estimated screed thickness of more than 40 mm, lightweight concrete is used, most often expanded clay concrete, less often more expensive concrete with foam glass.
It is important to properly dry the screed by covering it with a film or periodically moistening it. It is impossible to open the windows wide open, only ventilation through the vents or inclined sashes is allowed. The average maturation of a wet screed is a month, but before laying the coating, it is imperative to check the residual moisture of the concrete with an electronic moisture meter.
For experienced builders, provided that non-shrinking mixtures are used, the screed turns out to be quite even, it is quite possible to lay laminate and interlocking parquet board on it (over the substrate).
However, the base layer often requires a final leveling with a bulk mortar. Usually it is carried out after 7-14 days, when sand concrete (expanded clay concrete) gains about 70% of its strength, but some leveling agents are allowed to be laid only on a completely dried base.
It dries no more than a week and does not threaten leaks into the apartment on the floor below (this does not mean that you can do without a waterproofing layer). However, not all workers have experience with this technology, which increases the risk of marriage.
Theoretically, when installing a semi-dry screed, special equipment should be used – a concrete mixer, a pneumatic blower, tampers and trowels. But in practice, work is often performed manually, just trying to keep the water-cement ratio not exceeding 0.2 (instead of the usual 0.3-0.5). Such a mixture is difficult to lay and level, and the density and strength of concrete without machine compaction will be lower than with traditional recipes. Therefore, reinforcing polypropylene fibers (about 100 g per 10 l) are mixed with water. It is still desirable to level the layer with a trowel, although the use of leveling agents is also possible.
A serious disadvantage of a semi-dry screed is that only its thin top layer is strong enough, so it is not suitable for some finishing coatings, such as parquet and large-format tiles.
Dry prefabricated screed
The prefabricated screed consists of dry backfill and sheet flooring; in terms of strength and reliability it is inferior to concrete screeds, but it can be assembled very quickly. The backfill screed is lightweight, provides additional noise and heat insulation, and its thickness can be varied within 40-100 mm.
For leveling backfilling, expanded clay gravel of a specially selected fraction (to reduce shrinkage) is best suited , which is laid on top of a vapor barrier film and leveled along the beacons. Next, sheets are laid on a gypsum or cement basis; they are laid in two or three layers and fastened with screws, and then the joints are putty. It is also possible to use prefabricated two-layer floor elements with stepped edges.
Dry screeds made of high density mineral wool mats and plywood are much less common. Such a structure is more expensive than a backfill and cannot be used for leveling the floor – it only provides additional heat and sound insulation.
Any dry screed is afraid of moisture, therefore it is not suitable for bathrooms and kitchens, and after a leak, most likely, it will have to be partially dismantled. The compressive strength and peel strength of the surface layer is insufficient for the use of solid wood coatings – floorboards and block parquet. However, this is one of the best solutions for old houses with very uneven and also worn out and cold ceilings. The dry screed is ideally combined with interlocking parquet boards and laminates, and also allows laying linoleum, carpet and large-format porcelain tiles.
Floor on logs
When it is necessary to create a reliable base for a wooden covering and at the same time it is impossible to significantly increase the load on the floor, logs or (much less often) so-called modular raised floors are used. These structures allow you to eliminate any unevenness of the floor, but with a significant additional loss of ceiling height – not less than 50 mm (the minimum own thickness of the structure).
Logs are easiest to make from high-grade coniferous blocks and align with plastic wedges. Aluminum products on adjustable screw supports will cost several times more.
A tongue-and-groove floorboard is attached directly to the joists (with this design, their cross-section should be at least 50 × 50 mm), and parquet and parquet boards – to plywood flooring with a thickness of 16 mm. It is advisable to fill the space between the lags with expanded clay, fill with mineral wool or soft fibreboard – this will improve heat and sound insulation.
Modular raised floor
Modular raised floors help to quickly equalize any differences in the floor level and implement non-standard planning solutions. They are expensive and in apartments are used mainly for solving non-standard tasks, for example, arranging podiums of considerable height or laying ventilation and air conditioning systems under the floor on the basis of low-power installations.
The main parts of the raised floor are supports, stringers and slabs. The most common slab size is 600 × 600 mm, and the height of the supports varies from 50 mm to 1.5 m.
The supports can be made of plastic, steel or a combination of these materials. Floor elements are mainly made from high-density chipboard with a thickness of 38 mm. To prevent the emission of formaldehyde, they are lined with aluminum foil.
A more environmentally friendly solution is reinforced gypsum boards (on the websites of companies you can find the name “Calcium sulfate”), reinforced with steel sheet, but they are twice as expensive as chipboard.
When installing a raised floor, supports and slabs are installed at the same time. The supports are glued to the base with high-strength polyurethane glue or fixed with dowels. The position of each plate is controlled by level. Modular raised floors create an insignificant load on the ceiling, are quickly assembled and easily disassembled – this quality makes it easy to inspect and repair communications. Raised floors are combined with laminate and parquet boards, it is also possible to purchase boards with a finished coating.
When assembling prefabricated bases, noise is indispensable. As a reminder: in residential buildings (except for new buildings), repair work can be carried out from 9:00 to 19:00, a break from 13:00 to 15:00. Drilling is not allowed on Sundays and holidays.
At what stage should communications be laid?
- In a wet screed, cables can be embedded, as well as steel and polymer pipes with non-separable joints and an estimated service life of at least 40 years.
- When installing a dry screed, pipes and cables must be protected from contact with the backfill with strong ducts and casings to avoid damage from friction during shrinkage.
- It is easy to lay communications with log floors and modular raised floors. In the process of work, it is important not to reduce the section of the lag and not to increase the step of the supports.
Characteristics of base structures
|Construction type||Thickness min / max, mm||Average installation time by a team of two people, m2 / day||pros||Minuses|
|Wet screed||20/80||15–20; the topcoat can be applied no earlier than after 30 days||Strong, moisture resistant, compatible with any coatings, relatively inexpensive||Time consuming, creates a significant load on the floor|
|Semi-dry screed||30/80||15–20; the topcoat can be applied no earlier than after 10 days||The same as for a wet screed, plus not very high requirements for waterproofing the floor||Significant weight, low strength of the main layer, the need to use special equipment|
|Dry prefabricated screed||40/100||30-40||High assembly speed, good heat and sound insulation characteristics, low weight, relatively easy dismantling||Low moisture resistance, risk of deformation of the top layer under load and shrinkage during operation|
|Floor on logs||50/200||10-15||Durability, relatively easy dismantling; the structure is ideally matched to the wood flooring||Low moisture resistance, with a solid plywood base – high cost|
|Modular floor||50/1500||thirty||Fast assembly and disassembly||Very high cost, not suitable for many coatings|