Prestressed rib and block and hollow core slabs are usually classified as 30min fire resistant (CF30), but it is possible to enhance that resistance applying a suitable projected mortar.
In the most recent safety regulations, it is required that structural elements have a minimum fire resistance that in some buildings is incompatible with the use of prestressed rib and block or hollow core slabs.
Given the economic advantage of these structural solutions, it is cheaper in most cases to apply a fire resistant projected mortar on the lower face of the slab. There are products that enhance the fire resistance of the slab to CF60 class, with just 1cm thick mortar layer.
