Sand-cement floor screed

Screeding a floor seems to be the simple act of applying a mixture of Ordinary Portland Cement with graded aggregates and water to a floor base, in order to form a solid sub-floor that is capable of taking on the final floor finish. Nonetheless, as simple as this process might sound, screeding is one of the crucial element of a good floor and plays a major role in ensuring its quality, finish and durability.

For this reason, K.G. Bontira developed PLM-SC, a plant for applying the sand-cement screed with technical features that make it a unique equipment in its market segment. In the K.G. Bontira concept a good mixing becomes the focus of the entire production cycle. The commonly used technology for screeding overlooks indeed the good mixing of cement and aggregates, since the traditional screed pump cannot provide this action because the high filling degree and the short mixing time, that normally occur at the jobsite, being usually in a hurry.

GOOD MIXING MEANS GOOD QUALITY

As none of the mobile plants available on the market, the plant PLM-SC of K.G. Bontira has a pan mixer, which mixes the screed before the screed pump. Mixing means introducing energy to the system. This energy is used to improve the distribution of the cement in the sand mass and thus to optimize the microstructure of the blend. Several scientific studies demonstrate that an improved microstructure leads to higher mechanical strength, other things being equal.

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Sand-cement screed inadequately mixed: cement lumps (black) and air voids (yellow) in the screed mass

On the practical point of view, the better structure of the blend, obtained through the pan mixer, turns out in a better workability of the fresh screed and in higher compressive and pull off strength (adhesion) of the hardened screed. The better workability is immediately perceived by the applicator, who finds a lighter trowelling. The whole screed volume is then homogeneous and areas with predominant aggregates between area with excess of cement are no longer to find. Other things being equal, the required mechanical strength can be reached with lower cement: in this way cracking and curling due to the screed shrinkage are reduced

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Good mixed screed: cement (black) is evenly distributed in the sand structure (white to gray). Filaments of fibres are also visible.

Another not insignificant advantage of the mixing in the pan mixer is related to the use, more and more widespread, of chemical quality improvers. These admixtures can impart their action at the best if they have the necessary time and energy to interact with the cement. Time and energy that are given exactly by the pan mixer, the heart of the PLM-SC plant of K.G. Bontira. In this regard, K.G. Bontira can deliver an additive, Equo Smart, for the controlled drying of the screed.

Polymer fibres are also often used to improve the quality of the screed, since their effect on the microstructure control the shrinkage, reduces the microcracks and improves the flexural strength. PLM-SC of K.G. Bontira features an automatic dosing system for polymeric fibres. The fibres, delivered on rope rolls, can be supplied by K.G. Bontira (Smart Fibers).

K.G. Bontira delivers also qualified consultancy for the optimisation of the recipes.