- What you need to know
- Material selection
- Correct filling of the self-leveling screed
- Fill the decorative layer
Even a very high-quality concrete screed along the lighthouses inevitably contains defects and irregularities. Our advice site advises you to eliminate such blemishes with the help of self-leveling mixtures, some types of which can also be used as a ready-made floor covering..
What you need to know
A liquid consistency and finely ground components are what distinguishes a self-leveling screed from a conventional cement screed. True, in such mixtures, special additives are also used that normalize the solidification process, compensate for shrinkage, which is more pronounced due to the high water-cement ratio, improve the mobility of the mixture and give it additional strength..
And yet, the key difference lies precisely in the fine fraction of the filler, due to which the mixture can penetrate into the smallest pores and cracks and firmly stick to the base. Also, finely dispersed components allow the mixture to spread freely and form a perfectly flat surface with a layer thickness of only 2-3 mm. However, with all its advantages, the self-leveling mixture has an important disadvantage – the cost.
With such a screed, it is irrational to level the general slope of the floor and large pits. A self-leveling floor layer cannot be more than 10-15 mm, on average, its thickness is only 5-8 mm. This means that before pouring the self-leveling mixture, preparation must be carried out – an ordinary or semi-dry screed along the beacons. Its task is not only to eliminate the main irregularities and blockage of the subfloor, but also to create an airtight base that does not have even small cracks through which the liquid mixture can seep..
Before installing a self-leveling floor, it is extremely important to level and mark out. Using a laser axis plotter, mark the general horizon over the entire fill area and measure the level differences to determine the highest point, which is taken as a conditional zero mark. In areas where the understatement is more than 25 mm, preparation is carried out with a cement-sand screed, then a self-leveling mixture is poured.
For the correct installation of the self-leveling floor, it is enough to strictly adhere to the instructions drawn up by the manufacturer. But it should be remembered that even the exact adherence to the technology does not eliminate the troubles associated with low quality materials..
Only original materials should be used to fill the self-leveling floor. To do this, you should ask the seller for valid certificates of conformity and study what methods of protection against counterfeiting the selected manufacturer uses..
It is always better to give preference to brands that have proven themselves well in construction practice. Knauf and Ceresit offer the highest quality mixes, in case of peeling or deterioration of the coating, there is a high probability of a positive review of the complaint. However, with large volumes, buying a branded screed may not be affordable, in which case you can give preference to more budgetary mixtures of Vetonit or Volma, but you should buy them only from an authorized distributor.
Almost all manufacturers offer self-leveling mixtures based on cement and gypsum. Gypsum screed is cheaper, it is beneficial to purchase it for leveling floors with significant differences in plane. However, gypsum-based materials cannot be used in wet areas, moreover, the minimum thickness of such a screed is about 30 mm. Therefore, if the floor surface is well prepared, the best option would be a cement screed, which Our site has already described in detail..
When pouring a self-leveling screed, the most important thing is to ensure high-quality adhesion of a thin crust to the base. Otherwise, the floor will inevitably begin to roll, possibly also complete peeling and crumbling of the coating.
For pouring on concrete floors with low absorbency, it is necessary to use primers to increase adhesion, in the common people called “Concrete contacts”. They include a large amount of polymer glue and stone dust. It is better not to save money on basic priming and choose primers from a high price range, for example, Ceresit CT17 or POLIMIN AC-4.
When poured over a cement screed, high absorbency can disrupt the water-cement ratio during the setting period. Therefore, deep penetration primers should be used to reduce hygroscopicity and strengthen the base. For these purposes, compositions of combined action are suitable: Knauf Grundiermittel for gypsum compositions, Knauf Multi Grund or Litokol Primer L-m – for cement.
Before pouring along the contour of the room, a damper tape is attached to the glue close to the walls. It is necessary to compensate for shrinkage and thermal expansion. The thickness of the tape is chosen depending on the length of the screed in the direction perpendicular to the wall: from 4 mm for 3–4 m and up to 8 mm for 10–12 m. On the tape, mark the level to which the pouring will be performed. Professional teams use adjustable spider benchmarks for this purpose..
The maximum length of the screed, which can be filled with popular compounds, is approximately 12-14 m. In this regard, it is recommended to fill the floor in stages, separating the formwork sections with an area of no more than 25-30 m2 with manual cooking and about 60-80 m2 with machine feeding the mixture.
Correct filling of the self-leveling screed
If the self-leveling screed is prepared independently, only clean plastic buckets with a volume of 80-100 liters should be used for this purpose. After each portion, the container must be thoroughly cleaned, especially when working with gypsum compositions. Even the slightest inclusions of residues from the previous batch can affect the setting speed, while large fragments form irregularities on the finished coating.
To knead, you need a construction mixer with speed control and a spiral ribbon nozzle. The screed must be mixed carefully, avoiding foaming, while periodically cleaning the bottom and corners of the container with a spatula, where unmixed residues accumulate.
Due to the fact that part of the dry mixture will not be involved in preparation, a violation of the water-cement ratio is possible. For the same reasons, it is necessary to strictly adhere to the proportions indicated in the instructions, and not to use formulations that have been stored in open bags for a long time..
You can pour the mixture onto the floor in any convenient way, even by simply knocking over the bucket. The mixture is initially pushed with a mop to wet the entire floor surface, including the corners near the walls. After that, you can add the mixture to any place in the poured area until the level reaches the mark.
When the required layer thickness is formed, the screed should be rolled with a needle roller in order to displace the collected air bubbles. If a lot of air was entrained in the mix during mixing, the screed level after rolling may drop, especially with thick layers. In such cases, it is required to prepare and pour an additional portion of the mixture of the required volume..
During the setting period specified in the instructions, the screed must not be subjected to even limited mechanical stress. After hardening, cut off the protruding edges of the tape, lightly wipe the surface with an abrasive mesh to knock loose filler, and clean the floor from dust. The final stage is impregnation with a deep penetration primer, which is diluted with water in a ratio of 1: 3 and poured abundantly onto the floor. Both cement and gypsum binders require high humidity during the hydration period, so it will not be superfluous to periodically spray the floor with water.
Fill the decorative layer
After initial hardening for 4–7 days, finishing coatings can be laid on top of the screed or building materials can be stored. The surface is strong enough and does not get dusty; in technical rooms it can be used without additional processing. However, the story about self-leveling floors would be incomplete if not to mention the decorative self-leveling polymer compositions.
These are two-component epoxy resin based materials that produce a perfectly flat and smooth surface. Using powder dyes, you can set the floor to any color, or create an artistic composition by mixing several portions of different colors and pouring them into fancy streaks. It is also possible to fill in a white substrate and lay a self-adhesive printing substrate, followed by coating with a transparent protective layer..