Q.
When it comes to upper floor concrete slabs, the choice will be between a precast or prestressed product made by a specialist company, or a floor that is designed by an engineer.
Ready made systems include hollow core slabs and the beam and block systems that incorporate hollow blocks that improve insulation.
For floors in buildings of cellular construction up to four storeys high, hollow core slabs with finished soffits are usually the best choice. They are quick to erect and don’t have to be propped. If a long, uninterrupted span is needed then it is best to use one of the prestressed systems:
• beam and block,
• panel and topping, or
• hollow core.
The hollow core system is especially suitable for car parks, hospitals and supermarkets.
Another system that is often used in commercial or industrial situations involves a permanent galvanized metal or pre-painted aluminium framework that forms a supporting base for the concrete.
These ready-made floor systems are made by specialist companies and are designed by engineers, and they are all topped with fresh concrete on site. You will either work according to the manufacturer’s installation instructions or according to instructions specified by the consulting engineer on the project.
When an engineer designs a suspended concrete floor that is to be cast on site, he or she will determine the thickness of the slab and the strength of the concrete as well as whatever steel reinforcing is required.
Once concrete has been placed it should be kept moist so that it cures properly. The curing period lasts for five to seven days, and ideally foundation brickwork should only be laid after this period of time.