acoustic floor

First floor Fermacell acoustic flooring system installed.

This weekend we installed the acoustic flooring system by Fermacell throughout the first floor, which essentially creates a floating floor above the 22mm chipboard layer which was installed at the same time as the joists last year.

As described in a previous post this top layer forms an integral part of the whole system necessary for achieving the demanding standard of 45dB Rw airborne noise separation between storeys in the dwelling. It consists of 2 layers of 10mm thick Fermacell pre-bonded together and in turn bonded to a 10mm thick mineral wool layer, which is their '2E32' system. Together these layers arrive in a single board with a stepped profile around two edges, which allows for interlocking.

Starting at the top left corner of the room, the first step is to place a 30mm high x 10mm thick proprietary mineral wool perimeter strip around the edges of the room. As you can see here, due to the shape of the airtightness tape in the corners we had to cut smaller pieces of mineral wool to fit around the corner, and trim the board in a matching shape.

This will all be covered ultimately by the 45mm deep service cavity so will never be visible.

We then worked left to right and down the room, gluing the edges of each board in turn and screwing them together using the special Fermacell flooring screws, which are short versions of their proprietary wall screws to make sure the fixings only go into the bottom of the adjacent board and not the chipboard flooring below for proper acoustic separation. The screws are necessary to keep the boards together while the glue dries. (It is important not to use conventional drywall screws with Fermacell as the density of the board can cause them to break, and as they have a slightly different design they will not necessarily give the guaranteed pull-out strength.)

The glue is supplied in a bottle with a twin nozzle, which when pressed against the side of the board during application keeps each line of glue in the right place.

We cut the boards around the internal partitions, making sure there was 10mm perimeter mineral wool strip around all edges. We had to be neat here as we only have a 12.5mm wall board on these partitions (+ a 2-3mm plaster skim) with a shadow gap detail at the base, so we don’t have much tolerance to play with.

The final floor finishes will be oak parquet flooring stained black throughout the inner box, and a pale grey linoleum elsewhere.