Filigree slab composite floor slabs

A filigree floor is a composite slab: the thin precast plank, over 5 cm thick, arrives on site with the bottom reinforcement and lattice girders already in place, acts as permanent formwork, and the structural topping is cast on site. The plank is up to 2.50 m wide and up to 12 m long, the finished floor 14–40 cm deep, the concrete up to class C35/45. At 5 cm thickness the element weighs about 125 kg/m², and the bearing on the wall is 20 mm.

Every floor is drawn and calculated individually in our own design office, in line with the project specification and the structural requirements. Ceiling services — light points, speakers, ventilation and cable outlets — are integrated into the slab at the factory, together with empty conduits or provisions for later installation. Every insert is recorded in the technical documentation and, where necessary, allowed for structurally.

A clash monitoring system picks up conflicts between disciplines before production, not on the building site. Computer-controlled placement of the service inserts in the mould ensures accurate positioning.

In enquiries it appears as a reinforced concrete floor, ready-made concrete floors or a precast concrete floor. Filigree is the name of the technology in which the precast slab acts compositely with the topping cast on site.

Floor elements are covered by Declaration of Performance 03/26 and produced under Factory Production Control.

DoP 03/26 · Factory Production Control

A filigree slab is made of two layers created in different places. The lower one is a precast plate over 5 cm thick with the bottom reinforcement cast in and lattice girders projecting above it. The upper one is the structural topping poured on site, which fills the space between the girders and bonds with the plate into a single load-bearing section.

The lattice girder does two jobs at once. It transfers shear between the precast unit and the topping so both layers act as one element, and at the same time it stiffens the thin plate for transport and installation.

The underside comes out of the mould smooth and, once installed, forms the finished ceiling — ready for thin-coat plaster or wallpaper, with no levelling coat. That is what sets a filigree slab apart from a cast in place floor, where the soffit has to be levelled after striking the formwork.

Because the full section only exists once the topping has cured, the plate needs propping until composite action is reached. A solid floor slab does not — you will find the comparison of both technologies in the section above.

Element width is up to 2.50 m and length up to 12 m. The upper limit is set by transport rather than by the technology — an oversize load can be moved, but it changes the delivery cost and needs a route agreement, so we plan how the floor plan is divided into plates together with the transport envelope.

Precast thickness starts above 5 cm, and the total floor thickness falls between 14 and 40 cm. The exact value follows from the span, the structural scheme and the imposed load — we set it in the calculation for the particular floor, not from a catalogue.

At a precast thickness of 5 cm the plate weighs about 125 kg/m². That figure translates directly into crane selection and into how many units fit on a lorry, which is why we state it explicitly.

Service openings, penetrations and recesses are formed in the mould. The condition is that they appear in the documentation before production — drilling a finished plate cuts the bottom reinforcement, which here is the main load-bearing steel.

The standard bearing of the plate on a wall is 20 mm. The value is small because the floor ultimately works as a composite element — the final connection with the structure is formed after the top reinforcement is laid and the topping poured.

The sequence of works is fixed: set the props, lay the plates, place the top and support reinforcement, then pour the topping. Props are struck only once the topping has reached the required strength.

The bearing detail, the support reinforcement and the junctions with the remaining structure are set in the shop drawings. Every floor is drawn and calculated individually, so the bearing detail follows the structural scheme of that particular plan rather than a standard solution.

Manufacturing tolerances for the plate and the rules for its acceptance are covered on a separate page — deviations for floor plates in composite systems follow EN 13747.

The reinforcement table on this page covers slab spans from 2 to 8 m at imposed loads from 1 to 9 kN/m². This is the range in which the filigree slab works in residential, office and industrial buildings; larger bays are split into several plates with joint reinforcement.

The total thickness is not read from a catalogue. Whether the slab ends up 18, 22 or 30 cm thick depends at the same time on the span, the imposed load, the layout of permanent supports and the permissible deflection. We calculate this for every floor plan in our own design office and state it in the shop drawings together with the spacing of temporary props.

For the most common residential cases, i.e. spans of 4.5–6 m at 2–3 kN/m², the estimated total reinforcement from the table is 18–22 kg per plate, of which 6–7 kg is already in the precast element. The rest is top, support and ring-beam reinforcement placed on site before the topping.

The filigree slab is not the answer to every situation. It needs crane access, room for temporary props and a wet stage in the schedule. On plans fragmented into many small, irregular bays the advantage of precasting shrinks, and a solid slab that needs no propping after laying is worth considering.

We are a manufacturer, not a dealer: filigree plates are designed, produced and delivered from a single plant in Międzyrzecz, western Poland, about a hundred kilometres from the German border. Every slab is created as a model in Tekla Structures, from which the shop drawings, the laying plan and the reinforcement schedules are generated.

We deliver to sites across Poland and to Germany, the Czech Republic, Slovakia, Denmark and Sweden, within a radius of nearly 1,000 km from the plant, using regular external hauliers. Twenty to fifty trailer loads leave the plant every day, depending on how many sites are in the erection phase.

A plate up to 12 m long needs abnormal-load transport, shown in the offer as a separate item next to production and erection. Plates travel in laying order, numbered according to the plan, and go from the trailer straight onto the props; storing a thin plate on site means an extra lift and a risk of cracking.

Under our terms of contract, delivery guidelines are agreed three weeks before the date, and unloading takes up to two hours from the vehicle entering the site. We prepare a quotation from plans and sections usually within about a week, and changes to the plate layout are possible until the shop drawings are approved.

Composite slabs work wherever speed and a ready ceiling surface matter.

Precast elements are not priced from a per-metre price list — every element is designed for a specific project, and the difference between two projects of the same floor area can reach several tens of percent. So instead of a rate, we explain what actually determines the figure in your offer.

We prepare a quote within about a week of receiving complete documentation: dimensioned floor plans, sections, elevations and the site location with a postcode. The offer covers production, transport and installation — each item is priced separately, so you can see where there is room for savings.

The questions investors and contractors ask most often. Yours is not here? Write to us — we'll give you a straight answer.

Sections and connection details to scale — the same drawings that go into the technical catalogue. Numbers on the drawing refer to the list beside it.

Technical catalogue, installation manual, declaration of performance and FPC certificate — what design and handover call for.

Send us dimensioned floor plans, sections and elevations — we will prepare an element selection, a schedule and a quote. Preparing a quote takes around a week on average. We deliver and install across Poland as well as in Germany, Czechia, Slovakia, Denmark and Sweden.