Cutting a reinforced concrete panel up to 10 cm thick

In blocks of flats built from precast concrete panels, wall thickness depends on what the wall does. Loadbearing wall panels are usually thicker, often around 14 to 15 cm or more. Thinner panels of roughly 10 cm were common in many building systems as partitions between rooms, beside the kitchen or along the hallway. The exact thickness and the role of the wall vary with the building type and the year it was built, so always check it. A guess is not enough.

Typical reasons people order exactly this job:

• a new doorway in a concrete partition, for example from a bedroom into the kitchen,
• widening an existing opening for a wider door frame or a sliding door,
• a partial opening in the partition for a breakfast bar or serving hatch between kitchen and living room,
• shortening or trimming a precast element, a concrete slab or a balcony panel,
• an opening for ventilation ducts, larger pipes or an access panel.

Why does thickness matter so much? It decides which blade can cut the panel, whether one cut from one side is enough, and how heavy the removed pieces will be. At 10 cm an experienced cutter can still work fairly quickly and cleanly, as long as the room is ready.

The price list has a separate item for panels up to 15 cm. The difference is more than five extra centimetres. It shows in the method, the time and what happens to the removed concrete.

• Depth of cut: a panel up to 10 cm can usually be cut from one side with a handheld diamond saw using a blade of about 350 to 400 mm diameter, which still has some depth to spare. At 15 cm the cutter often has to saw from both sides or use a larger track-mounted wall saw.
• Accuracy: when cutting from both sides, the two cuts must meet exactly in the middle of the wall. With a thin panel and a single pass this problem disappears, and the edges are usually straighter.
• Weight of the pieces: reinforced concrete weighs roughly 2.5 tonnes per cubic metre. One square metre of a 10 cm panel therefore weighs about 250 kg, and at 15 cm about 375 kg. Even a thin panel is cut into smaller pieces, but a thicker one needs more of them.
• Role of the wall: thin panels are more often partitions, thick ones more often loadbearing walls. This is not a fixed rule, but at 15 cm the chance of cutting into the structure is higher, and so are the demands on the structural engineer and on strengthening the opening.
• Time and water: a deeper cut takes longer, uses more water and produces more slurry. At 10 cm the job is shorter and puts less strain on a lived-in flat.

Not sure which item you need? Measure the wall in an existing opening, for example at a door frame, and subtract the plaster or skim coat. What counts is the thickness of the concrete, not of the whole wall with its finishes.

Is the wall loadbearing or not?

This is the first question, and the answer belongs to a structural engineer, not to the cutter or a neighbour. Even a thin panel can carry load or stiffen the building in some systems. The engineer decides whether the opening is possible, how big it may be and whether it needs strengthening, for example with a steel frame. Without this assessment, nobody should cut into a panel in a block of flats.

Building management, owners and the building authority

In a block of flats the wall is part of the shared structure, even though it stands inside your flat. Discuss the work with the building management or owners' association first. They usually ask for drawings or a structural report. Whether your alteration needs approval, a notification or another procedure depends on local building regulations, so check with your local building authority. Do not assume that a simple notice is enough: for openings in panel walls it often is not.

Cables and pipes in the wall

Panels often contain cables, back boxes and sometimes pipes cast into the concrete. Before cutting, the circuit must be switched off and any cables at the cut line rerouted. This work belongs to a qualified electrician. A cable detector helps, but in older buildings it is not fully reliable, so also trace likely cable runs from switches and sockets.

The work area

Before the cutter arrives, you should have:

• a clear space of at least two metres on both sides of the wall,
• floors and furniture covered, ideally with plastic sheeting and rigid boards against falling pieces,
• access to water and power; some saws need a three-phase socket, so ask in advance,
• the opening marked according to the drawings, with the exact sizes of the door frame or steel frame,
• removal of the concrete pieces and slurry arranged,
• neighbours informed, and working hours kept in line with the house rules.

Marking out and measuring in linear metres

The cutter marks the outline of the opening on both sides of the wall following the drawings and checks it with a spirit level or laser. The price is per linear metre of cut, meaning the total length of all cuts. For a doorway 90 cm wide and 200 cm high, that is two vertical cuts of two metres each and one horizontal cut at the top, roughly 4.9 linear metres in total. If the bottom at floor level also needs cutting, another cut is added. Extra cuts that divide the opening into smaller pieces are often counted as well, depending on the agreement, so settle in advance how the cutter will measure.

Propping and securing

If the engineer requires it, temporary props go in above the opening before cutting, or the top part of the steel frame is fitted first. The section being removed is secured so it cannot fall when the last cut is finished. In practice cutters use wedges, spreaders or anchored brackets that hold the piece until it can be lifted out under control.

The cut itself

For a panel up to 10 cm the cut is usually made from one side with a handheld electric or hydraulic saw with a diamond blade. The blade goes through the concrete and the steel mesh in one step. Wet cutting is the normal method: water cools the blade and binds the dust. Where water is not possible, the cut is made dry with an H-class industrial extractor that captures fine silica dust. This dust is harmful to health, so take it seriously even on a short job.

Corners of the opening

A circular blade working from one side cannot cut a sharp right angle without running slightly past the corner. There are two options. The cut can overrun a little at the corner, which is quick but leaves a short slot in the wall. Or the cut stops short of the corner and the corner is finished by hand, with a smaller saw or by core drilling. On loadbearing or structurally sensitive walls the engineer usually will not allow overcuts, so decide this when you place the order.

Cutting into pieces and removal

The area of the opening is cut into pieces that two people can carry safely or move on a trolley. At 10 cm thick, a 50 × 50 cm piece weighs about 60 kg, still manageable for two. Pieces come out one at a time from the top, so none drops onto the floor or someone's feet. Finally the slurry is vacuumed up and the edges cleaned.

The cutting itself is not a job for an amateur. It is a structural alteration that needs proper equipment and dust control. What you can do safely is get the room ready, which shortens the cutter's visit and protects your flat. Leave anything electrical to the electrician.

1. Confirm the structural engineer's approval and the size of the opening in writing.
2. Measure the concrete thickness in an existing opening, without plaster or tiles, and pass it to the cutter.
3. Empty both rooms within at least two metres of the wall.
4. Lay plastic sheeting on the floor, tape the edges and cover it with rigid boards where pieces will come out.
5. Seal doorways to other rooms with sheeting and tape to keep out dust and spray.
6. Check the floor at the base of the wall for gaps where water could run down to the flat below, and tell the cutter about them.
7. Mark the opening lightly in pencil on both sides according to the drawings and the door frame supplier's sizes.
8. Clear a route to the lift or stairs and protect the floors of the common areas if the building management requires it.
9. Arrange a skip or bags for the concrete and confirm who takes away the slurry.

A thin panel is simpler than a thick one, but individual jobs still vary a lot. That affects the time needed and the final cost.

Things that make it easier:

• free access to the wall from both sides and empty rooms,
• an empty flat during renovation, where water and noise do no harm,
• a lift or a low floor, which shortens carrying the pieces out,
• a precisely marked opening and a clear decision on the corners,
• cables already rerouted.

Things that make it harder:

• a lived-in flat, where floors, furniture and neighbouring rooms need careful protection from water and dust,
• dry cutting with extraction, which is slower than wet cutting,
• denser reinforcement, steel inserts in the panel or cast-in frames that slow the blade,
• cuts right next to the ceiling, the floor or a corner, where the saw cannot sit flat,
• corners without overcuts, which have to be finished by hand,
• a high floor with no lift and a long route to the skip,
• ceramic tiles or thick layers on the wall, which must be removed first or cut as well.

Cutting the panel is one step in a chain. If the trades are not coordinated, the opening may sit unsupported for days or work gets done twice.

1. The structural engineer designs the opening and any strengthening.
2. The electrician reroutes cables at the cut line.
3. Strip-out work removes tiles and floor layers if they are in the way.
4. The cutter makes the opening and removes the pieces.
5. A steel fabricator or builder fits the steel frame if the engineer requires one, usually straight after cutting.
6. A plasterer or builder makes good the edges, the door frame goes in, then decorating and flooring follow.

Cutting a doorway in a panel up to 10 cm usually takes a few hours including setup and clean-up. A larger opening or several openings in one flat can take a full day. The concrete itself does not need to dry like plaster, but after wet cutting the walls and floor usually need time to dry before the next trades, especially before gypsum plaster or a timber floor. Adhesive and plaster manufacturers state the maximum moisture content the surface may have.

If the opening is to get a steel frame, have it made to the exact sizes measured after cutting, not to the drawings. There is often a difference of a few millimetres between drawing and reality, and with a frame that matters.

Most problems do not start with the cut itself but before it or just after.

• Cutting without a structural assessment. The wall looks like a partition but carries load. Later, cracks appear above the opening or in neighbouring flats, and the repair is complicated.
• Overcuts at corners where they were not allowed. The slots weaken the corners of the opening, and hairline cracks can run from them.
• A cut cable. A power cut is the minor problem. A short circuit or damage to a neighbouring circuit is worse. Always switch off and reroute cables beforehand.
• An unsecured piece. It falls, damages the parquet or tiles, or injures someone.
• Water in the flat below. During wet cutting, water runs under the wall or through voids in the floor. Careful damming and continuous slurry extraction prevent it.
• Exposed steel left unprotected. Cut bar ends on the edge of the opening rust over time, and the plaster above them cracks or shows rust stains.
• Opening cut to the wrong frame size. The opening is too tight or too wide and the frame has to be packed out. Check the sizes directly with the door supplier.
• A long wait for the frame. If the engineer required strengthening, the opening should not stay without it for long.

Inspect the opening straight after cutting, while the cutter is still there. Any trimming is easy at that point. At handover, check:

• Opening sizes against the drawings and the door frame or steel frame, measured at the top, middle and bottom
• Plumb vertical edges and a level top cut, checked with a spirit level or laser
• Flat cut faces without noticeable steps or broken-out areas
• Corners finished as agreed, with or without overcuts
• No new cracks in the panel, ceiling or adjoining walls
• Condition of the cut reinforcement and agreement on who protects it against corrosion and how
• Undamaged wiring and working circuits once the breakers are switched back on
• Concrete pieces removed, slurry vacuumed and floors clean
• No water leaked to the neighbours, especially the flat below
• A record of the linear metres actually cut that matches the agreed method of measuring