Filigree originally refers to an art technique in which fine metal wires are formed into an openwork pattern. In construction the term is used mainly for the filigree concrete slab (also called wide-slab or half-slab): a prefab concrete slab only a few centimetres thick, with reinforcement and a protruding lattice girder, completed on site with cast-in-place concrete.
Filigree in construction
Filigree slab (wide slab)
- Lower face of precast concrete (50–70 mm thick)
- Steel lattice girder on top
- Protruding reinforcement at the upper face
- Topping concrete poured on site
- Ends up as a monolithic floor
Filigree wall (double wall)
- Thin precast shell with reinforcement
- Two shells with a cavity between
- In-situ core poured on site
Advantages of the filigree system
- Fast execution — no full formwork required
- Smooth soffit — no plastering needed underneath
- Dimensionally stable — produced in controlled factory conditions
- Flexible design — easily tailored to any plan
- Material efficient — combines precast and in-situ
Application
Filigree slabs are widely used in:
- Residential construction — floors for apartments and houses
- Commercial buildings — offices, schools, hospitals
- Industrial buildings — production and storage halls
- Car parks — upper-level decks
- Roofs — as a load-distributing layer
When placed, the filigree slab rests temporarily on props until the topping concrete has reached sufficient strength. The lattice girder provides both stiffness for transport and placement, and shear connection between precast and in-situ concrete.
Filigree as art
In smithing and goldsmithing, filigree is a centuries-old technique in which fine gold or silver wires are soldered into flowers, scrolls and patterns. In architecture this ornamental form appears in:
- Wrought-iron gates around palaces and churches
- Balcony railings in Art Nouveau buildings
- Stained glass with fine lead lines
Related terms
- Wide slab
- Precast
- Concrete
- Hollow-core slab
- Lattice girder
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.