Dry assembled floor screed over expanded clay backfill

I start a job with a laser and a tape measure, not with a delivery of materials. The first two things I need to know are the real drop across the room and what the base underneath is willing to carry. A wet screed that swallows an eighty millimetre difference adds well over a hundred kilograms to every square metre, and on old timber beams or a thin panel slab that weight is not a detail — it is the reason the ceiling below starts to crack. A dry assembled floor solves exactly the same geometry at a fraction of the load, and it does it without a single bucket of water in the flat. That is why I offer it in occupied apartments, in offices that cannot close for three weeks, and on any base where the structural reserve is already spent.

The build-up is simple and it only works if every layer is done honestly. A vapour barrier goes over the base with generous overlaps between sheets and a turn-up onto the walls above the level of the finished floor. Edge tape runs around the whole perimeter, around every pipe penetration and through the door openings — this is the strip that keeps the floating floor from touching the walls, and skimping on it is the single most common reason a dry floor starts talking underfoot a month later. Then the backfill: dry expanded clay granules poured to the marks, levelled along temporary rails set from the laser plane, and compacted so the layer stops moving under weight. I pull the fill bay by bay, lift the rails as I go and fill the grooves behind me.

Sheets go down in two layers, staggered, so that no joint of the upper layer ever sits over a joint of the lower one. Every element is bedded on adhesive and drawn together with self-tapping screws at a fixed spacing, heads sunk flush, seams filled and sanded. Pipework and cable can run inside the backfill in protective conduit — I agree the routes with you first and photograph them before the sheets close everything up. Since nothing has to cure, laminate, vinyl, engineered board or tile can be laid the same day the floor is finished. One room is usually a single day; a flat of sixty to eighty square metres takes three to five working days including setting out, backfill, sheeting and clean-up.

What is included:
— laser survey of the drop and a written build-up thickness for each room;
— vapour barrier with overlaps and wall turn-ups;
— edge tape along walls, columns, pipes and openings;
— expanded clay backfill levelled to beacons and compacted;
— two layers of sheets, staggered, glued and screwed, seams filled;
— conduits for pipes and cable with a photo record before closing;
— removal of debris and a floor handed over ready for the covering.