Structures in reinforced or pre-stressed concrete and flooring in masonry and concrete are already cast and laid or supplied already sized for the fire-resistance rating required when the building is constructed. This sizing is obtained by ensuring an adequate concrete cover to act as insulation for the inner metal component. If the building is subject to a change of use or an increase in the fire load and in other situations, a fire-resistance rating higher than that previously required may be necessary. In such situations this can be achieved by increasing the thickness of the concrete cover, adding some layers of concrete, or by the use of passive fire-protection systems. This also applies to concrete and masonry flooring.
Protective coatings for reinforced and pre-stressed concrete structures are normally divided, according to their application, into intumescent paint, spray plasters and covering panels.
The choice of protective system to apply in the various situations planned for, takes many different factors into account, for example architectural needs, economic factors, environmental conditions, and the fire-resistance rating prescribed for the building.
In particular, reactive paints and varnishes when applied look just like normal paint or varnish and they do not alter the appearance and the geometry of the structural elements to which they are applied. In the event of fire however, as the temperature rises, they react chemically, changing into a carbonaceous foam with excellent thermal insulation properties, whose thickness swells to 80/100 times that of the original coating, acting as an effective temporary protective barrier.