Breaking Out (Demolition) of Reinforced Concrete Slab up to 12 cm

Concrete handles squeezing very well, and steel handles pulling. Together they form a strong unit that holds together even after the concrete has cracked. That is why reinforced concrete is not just a job for a hammer. The concrete breaks into lumps, but the reinforcement stays in place as a mesh and has to be cut out bit by bit. You end up with two kinds of waste: broken concrete and steel.

A slab up to 12 cm counts as a thin one. In practice this usually means it can be handled with a hand-held demolition breaker, without heavy machinery. It is still heavy, noisy and dusty work, and before anyone starts it has to be clear what job the slab is doing in the building.

The key question is simple: is the slab load-bearing? A ground-bearing floor slab in a garage usually carries nothing above it. A floor slab between storeys, a balcony, or a slab with partition walls standing on it, is part of the structure. In that case a structural engineer has to set out the method: whether and how the structure must be propped temporarily, and in what order the slab can be removed.

• Building authority: work on load-bearing parts of a building normally falls under local building regulations and often needs approval. Check with your local building authority before work starts, and keep the engineer's report ready.
• Flats: in a block of flats, speak to the building management or owners' association first. Floor slabs and balconies are often shared parts of the building.
• Services: find out what runs inside or under the slab. Electricity, water and gas in the work area must be disconnected. Gas work must be done by a qualified, registered gas engineer, and electrical work by a qualified electrician.
• Old floor layers: in older buildings, the tiles or adhesives on top of the slab sometimes contain asbestos. If you suspect it, have a sample tested. Asbestos removal belongs to a licensed specialist firm.

If a gas pipe is damaged during the work despite all precautions, stop immediately. Do not switch any electrical devices on or off, no flames, open windows, leave the area and call your gas supplier's emergency line or the local emergency number (112).

1. Mark out the area to be removed and check the slab thickness with a trial hole or core.
2. For a load-bearing slab, install props as instructed by the structural engineer.
3. Seal off the work area with plastic sheeting and cover windows, doors and air vents.
4. Cut along the edge with a diamond blade so the breaking does not spread into the part that stays.
5. Break the concrete with a demolition breaker in small sections, working from the free edge inwards.
6. Cut the exposed reinforcement bars with an angle grinder or hydraulic shears.
7. Carry out and sort the waste as you go: concrete in one pile, steel in another.
8. Clean up the edges and prepare the base for the next layer.

Where part of the slab is staying, for example when cutting an opening for a staircase or a drain pipe, always cut the edge first. Without a cut, cracks easily run into the remaining slab.

For slabs up to 12 cm, the usual tool is a hand-held electric demolition breaker. It suits flats, cellars and smaller areas where a machine cannot get in and where the work needs to be precise with little vibration.

Machine breaking with a hydraulic breaker on a mini excavator makes sense for larger outdoor areas, such as a terrace or the floor of a large garage. It is faster, but it needs access for the machine and causes stronger vibration.

Diamond cutting is the choice where you need a clean edge or where vibration has to be kept low, for example when cutting an opening in a floor slab. The whole slab can also be cut into blocks and carried out in one piece. Cutting with water also reduces dust a great deal.

How much effort, and therefore time and cost, the job takes depends mainly on these factors:

• Amount of reinforcement: a dense mesh or thick bars slow the work down more than the concrete itself.
• Concrete quality: old, crumbling concrete comes out more easily, while hard concrete takes more time and tools.
• Access: working in a cellar, upstairs or in a tight space means hand work and carrying the rubble out by hand.
• Suspended floor slab: propping, careful work from above and protecting the room below all add time.
• Waste: loading, transport and disposal of concrete at a recycling site or landfill is a big part of the job. The steel can go to a scrap metal dealer.
• Surroundings: an occupied house, neighbours behind the wall and limited hours for noisy work all mean slower progress.

• Breaking without checking whether the slab is load-bearing. With a floor slab or balcony, this can end with part of the structure collapsing.
• Underestimating the reinforcement. Without tools for cutting steel, the work stalls and bars get torn out together with the surrounding concrete.
• No cut along the edge. Cracks spread into the part of the slab that was meant to stay.
• Heavy vibration near other structures. It can crack plaster and the neighbours' tiles, or damage pipes and cables.
• Dust without protection. Concrete dust contains crystalline silica, which harms the lungs. Wear an FFP3 respirator, safety glasses, ear defenders and gloves.
• Mixed waste. Concrete mixed with plastic, timber and steel is harder to hand in for recycling.

• The slab has been removed over the agreed area and the edges are straight and sound
• There are no new cracks in the part of the slab that remains
• Reinforcement at the edges is cut back or left exposed as the structural engineer specified
• Surrounding walls, plaster, pipes and cables are undamaged
• Props under a load-bearing slab stay in place until the structural engineer decides they can come out
• The waste has been taken away and you have a receipt or waste transfer document for it
• The area is cleared of rubble and dust and ready for the next stage