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Perlite for Floating Floor Finishes that Reduce Sound Transmission
A Presentation of Dr. Hans Pape
former managing director of Deutsche Perlite
May 1977

There is a trend in modern construction towards the use of lightweight building components in place of traditional heavyweight materials.

In the search for a lightweight floor design that has the added feature of sound attenuation, a floor design has been developed in Europe that is known as a "floating floor finish".

Floor Finish vs. Floating Floor Finishes

Floor finishes are layers of flooring applied as a screeding mortar in a plastic consistency to the existing, previously cleaned structural concrete sub-floor, which harden after setting to form a wearing surface. They serve primarily to level uneven rough sub-floors and usually consist of a sand/cement mixture. They are also termed composite floor finishes. The surface of a composite floor finish should be of such a quality that any type of floor covering can be applied to it.

If the floor finish is separated from the rough sub-floor by an insulating layer, such floor finishes are then defined as 'floating floor finishes'. They are neither in contact with the rough sub-floor nor with the walls and are therefore isolated from the structure. They float on the insulating layer and merit therefore the term "floating floor finish". Before discussing particulars of the floating floor finish, it is necessary to explore sound transmission through walls and especially floors.

Noise Transmission in Structures

More than 90% of all floors in apartment and office buildings in Germany are constructed of reinforced concrete. This type of construction exhibits good protection against airborne noise both by virtue of thickness (from about 150mm) and by weight. This type of construction does not offer protection against transmission of impact noise.

In the transmission of impact sound, noise is generated by direct contact with the floor, for example by walking or by moving chairs. ,It is subsequently reflected on the other side of the floor as sound transmitted by air.

The floating floor finish, which is separated by a resilient insulating layer both from the structural concrete sub-floor and from adjoining rooms, is effective in this situation. The resilient insulating layers in Germany usually consist of slightly compressed fiber boards or board manufactured of inorganic fibers such as glass-fibers or rock-wool applied over a loose perlite fill.

In both types of noise transmission, particularly in impact sound, the transmitted sound not only penetrates the respective separating surface ,but also the adjoining construction components. The floor induced to vibrate by the impact sound, conduct the sound waves both through the floor into rooms located below and also through the walls firmly connected with it into adjacent rooms.

Mandatory sound reduction values have been established in Germany for more than 20 years in DIN 4109 which must be strictly adhered to not only in the home building industry; but also in the construction of hospitals, schools, and office buildings. Compliance with established sound reduction values through use of appropriate standards has been made possible in Germany, because methods have been found to prevent the transmission of noise into adjoining rooms completely or to an extent where they were no longer regarded as bothersome , without incurring excessive building costs.

Installation of Floating Floor Finishes

Prior to the application of the floor finish, water-repellent paper is placed over the insulating layer and border strips are fastened on the plaster walls and rising masonry to prevent transmission of the sound to the adjacent rooms. Border strips are generally made of fiber board.

A determining factor for the sound reduction quality of a fiber board is its inherent elasticity, which affords a cushioning effect. The applicable measuring unit is the "dynamic stiffness" which determines the quality of the sound reduction material for the protection against impact sound with respect to a floating floor finish.

It is important to point out in this connection that a perlite fill installed under a floating finish cannot be judged according to its dynamic stiffness. Although a perlite fill does not have any significant inherent elasticity, it does provide satisfactory sound attenuation improvement values under the floating floor finishes. In a perlite fill, the destruction of the sound energy and thus the lessened transmission of sound is essentially accomplished by friction on the contact surfaces of the individual grains of perlite.

A level-surfaced perlite fill cannot be directly walked on. It must be covered with sturdy corrugated paper or soft fiberboard made of wood fiber, prior to applying the water-repellent paper and subsequently the floor finish. Most of the floor finishes laid over a sound-insulating base consists of cement as the bonding agent and sand as aggregate. The thickness of the floor finish depends on the thickness and springiness of the insulating layer.

When the first floating floor finishes were installed in Germany, it was thought that such a thin concrete plate of a floor finish had to he reinforced under all circumstances with steel, in order to prevent it breaking or tearing. Nowadays it is recognized that this is not necessary. None of the cement floating floor finishes applied today arc reinforced. The only important factors are the correct composition of cement and aggregate material as well as exact processing according to the instructions in DIN 4109.

The thickness of a floating cement floor finish is only 35mm to 45mm. Such a floor finish can nevertheless withstand all loads occurring in apartments and office buildings. In addition to cement floor finishes, floating anhydrite and asphalt floor finishes are widely used.

Besides asphalt floor finishes, other dry floating floor constructions have gained in importance during the last few years such as large tongued and grooved chipboard sheets, manufactured in 16mm and 22mm thickness; and finished parquet components which are put together on multi-tiered soft fiber boards. These prefabricated floor constructions require a complete level base and an equalization of height; both of these conditions are fulfilled by perlite loose fill.

With a floating floor finish, the sound insulation is always present as an integral part of the structure. Sound insulation can be improved even further by a suitable floor covering.

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed.  Your supplier may be able to provide you with more precise data.  Certain compositions or processes involving perlite may be the subject of patents.
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