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The article “Noise insulation of floor” presented various options for reducing noise from the downstairs neighbors. In this article we will discuss in detail the most popular option for soundproofing the floor - the "floating" screed. Let us remind that the floating screed is essentially a conventional screed applied over the soundproofing base. The damping layer prevents the screed from rigid contact with the floor and the walls. This results in high vibration insulation of your floor against the building frame! If the screed is made properly, then the noise insulation of floor will increase significantly and meet the norms of the Building Codes and Regulations (SNiP) “Noise protection” with surplus.
Screed is the building structure which must not only increase the sound insulation but also feature the structural stability and certain robustness to withstand the weight of people and furniture and be structurally stable. To comply with these requirements, the allowable thickness of the screed is restricted to minimum 50 mm. A thinner screed may crack in the points of maximum load (the doorways or the area under the cabinet).
According to the building codes, each screed (even applied directly over a concrete base) must be reinforced. In the case of "floating" floors, the reinforcement of the screed is mandatory and the metal mesh with a cell of 5 x 5 or 10 x 10 cm (usually BP-1 is used with wire thickness of 3-5 mm) should be used as a reinforcing element. If the reinforced with metal mesh screed cracks, no problems will occur. But if the reinforced with fiber or other substitutes screed cracks then its fragments may displace by several millimeters due to the elastic base.
The need in the levelling screed depends on the floor structure (whether the difference, cavities, protrusions and other defects are available) and the soundproofing materials which will be placed under the screed. In general, the allowable difference within one room should not exceed 2 cm. The levelling screed can be made of expanded clay spilled with cement milk or polystyrene concrete; both options are quick-drying and do not load strongly the floor structure.

The levelling screed is also required if wiring or water supply pipes are laid over the floor structures.
After levelling with the roughing screed, the soundproofing materials should be placed on the floor. It is important to bend the sound insulation to the walls so that the future screed contacts with neither the floor nor the walls. When using MaxForte-SoundPRO и ShumoIzol materials, the joints between adjacent cloths should be glued with waterproofing mastics or reinforced assembly tape. The materials serve as a waterproofing, that’s why you can immediately pour the screed after laying them. When using the 110 kg/m3 MaxForte-ECOslab sound-absorbing slabs, the slabs should be joined and covered with a construction polyethylene film from above. This is necessary for the screed solution could not penetrate into the body of the slabs.
It is best to make the screed of brand M300 sand concrete. From the point of view of sound insulation, a thicker screed should be always preferable: increasing thickness makes the weight – and hence the sound insulation – raising! In most cases, the surface density of sound insulation screed is 80–120 kg, which corresponds to a thickness of 5–7 cm. In pursuit of sound insulation, the carrying capacity of the floor structures and the resonant phenomena of the oscillatory systems should be remembered. Without delving into the physics of the process, it must be noted that the surface mass of the screed should not exceed 75% of the surface mass of the floor structure.

Never try to lighten the screed by adding the expanded clay or the polystyrene – this will decrease the efficiency of the structure!

If there are internal walls in the apartment, the screed should be poured at each room separately. If there are no partitions and they are planned to be built from foam concrete blocks or gypsum partition blocks, then the partitions first should be erected and only then the screed should be poured. If the partitions are planned to be made of drywall, then the screed first should be poured all over the apartment and then the partitions should be erected. The maximum area of the floating screed should not exceed 40 m2. If it is necessary to cover a greater area (or the room is longer than 8 m in length / width), the screed should be poured by parts and the movement joints should be arranged between these parts.

Our experts professionally mount the sound insulation of apartments in houses and offices, therefore this technology has been tested in practice. And the practice shows that the “floating” screeds can never be perfectly smooth. This is caused by difficulties with the accurate setting of leads over the elastic sound-insulating layer. The floor surface can be levelled finally using a self-levelling compound (a self-levelling floor).