How to prop a floor slab before opening a stair or lift opening

Opening a hole in a floor slab —for a staircase, a service shaft or a lift— is not a demolition like the others: the element being removed was designed to work as part of a continuous slab, and taking it out changes the structural behaviour of what remains around it.

It isn't enough to prop only the area being demolished

Slab demolition removes a slab or part of it, usually to open a stairwell, service shaft or lift opening. The rule that can't be skipped: always work from external supports or by propping the adjoining area, not only the one to be demolished. When part of a slab is removed, the adjacent section may end up working differently from how it was originally designed — the slab around the new opening carries loads that were previously distributed in another way.

Disc cutting: mark the limits before demolishing

Disc or chasing-saw cutting makes a clean pre-break before demolition, so the fracture doesn't spread uncontrollably into adjoining areas. It is especially useful for opening an exact hole in a wall or slab without damaging the rest: first mark out the cut and demolish afterwards inside that line, instead of breaking out by hand with no marked limit, which can crack areas that were meant to stay intact.

Why this isn't a job to improvise

A slab badly propped during demolition, or a fracture that spreads further than expected because the cut wasn't delimited, are among the most expensive faults to correct on site — it isn't just a finish problem, it's a structural safety problem that may require additional reinforcement to put right.

Frequently asked questions

Is it enough to prop only the section of slab I'm going to remove? No: the adjoining area must also be propped, because the slab remaining around the opening works differently from how it was originally designed.

What is cutting with a disc before demolishing by hand for? To mark exactly where the area to be demolished ends, preventing the fracture from spreading uncontrollably into areas that must stay intact.

Can a slab opening be made without a technical project? In most cases no: as a structural element, it requires calculated propping beforehand and, almost always, the approval of a responsible technician.

Conclusion

Propping the adjoining area, not only the one being demolished, and marking the limits with a prior cut before breaking out are two measures that separate a well-executed structural opening from one that compromises the safety of the rest of the slab. In this type of demolition, prior technical care weighs more than speed of execution.