Cutting Reinforced Concrete Panels (Openings, Windows, Doors) up to 15 cm

This job covers two closely related items. The main difference is the thickness of the concrete. Thickness decides which machine is used, whether a cut from one side is enough and how long the work takes.

• Cutting up to 10 cm mostly applies to thinner panels and partition walls. Typical jobs are a new doorway in a partition, enlarging an existing opening or cutting out an old steel door frame.
• Cutting up to 15 cm is for thicker panels. In panel buildings these are often load-bearing walls, so the structural side needs even more care.

You do not have to guess the thickness. You can measure it at an existing opening, for example next to a door frame. It is also shown in the building's drawings, which the building management usually keeps.

Why does this matter so much? A load-bearing panel carries the weight of the floors above. If an opening is cut without a proper design, cracks can appear, the concrete above the opening can sag and, in the worst case, the stability of part of the building can suffer.

How do you tell a load-bearing wall from a partition? Load-bearing walls are generally thicker and partitions thinner, but thickness alone is not proof. The building drawings and a structural engineer give a reliable answer. If the wall is load-bearing, the engineer sets the size and position of the opening. They usually also specify steel strengthening, such as a frame or a lintel made from steel sections.

In a flat, this is never only your decision. Discuss any change to the load-bearing structure with the building management or owners' association before work starts. Building regulations differ from place to place, so ask your local building authority what kind of approval your change needs. Do not assume that a simple notice is enough. Check before you book the work.

1. The contractor visits the site, checks the panel thickness and, for a load-bearing wall, asks for the structural engineer's design.
2. The opening is marked out precisely on the wall to suit the door or window. A small margin is left so the frame can be fitted.
3. The cutting line is checked for electrical cables, water, gas or heating pipes. Any services are switched off or rerouted.
4. For a load-bearing wall, the ceiling is propped before cutting starts. The steel strengthening is installed as the engineer specifies.
5. The surrounding area is covered with plastic sheeting, and the floor is protected against water and slurry.
6. The panel is wet-cut with a diamond blade. Thicker panels are often cut from both sides, and the two cuts must meet exactly. Holes are sometimes core-drilled in the corners so the saw does not overcut beyond the opening.
7. The cut-out block is split into smaller pieces that can be carried out safely. The pieces must never be allowed to crash onto the floor.
8. Finally, the slurry is removed, the edges are tidied and the waste is taken away.

A hand-held diamond saw is the usual choice in flats. It is mobile, fits into smaller rooms and cuts fairly cleanly with water cooling. A thinner panel up to 10 cm can often be cut from one side. At up to 15 cm, the work is usually done from both sides.

A track-mounted wall saw is used for larger openings and where a perfectly straight edge matters. The rail guides the blade for an accurate cut with less vibration.

Core drilling suits round openings for pipes, cables or ventilation, and the corners of rectangular openings. It is not used to cut a whole doorway.

An angle grinder with a diamond disc is only good for small adjustments and trimming. It does not cut deep, makes a lot of dust and leaves rougher edges.

• Panel thickness. Thicker concrete means slower progress, more blade wear and more need to cut from both sides.
• Load-bearing wall. This adds a structural engineer, propping and fitting the steel strengthening.
• Access. A narrow hallway, an upper floor without a lift or little space around the wall all add time to preparation and to carrying out the pieces.
• Water and power on site. Wet cutting needs a water supply and slurry extraction. If these are missing, another solution has to be found.
• Services in the wall. Moving a cable or pipe is a separate job for a qualified electrician or plumber. Gas pipes must always be handled by a qualified, registered gas engineer.
• Waste. Reinforced concrete is heavy and does not go in household bins. Plan for construction waste removal in line with local rules.

• Cutting without a structural engineer. In practice, people often treat a wall as a partition just because it "looks thin". Putting the damage right is usually far harder than getting an assessment first.
• Inaccurate marking. An opening with no margin for the frame has to be cut again. One that is too large has to be built back up.
• Cut services. Cables and pipes inside a panel cannot be seen from outside, so their routes must be checked beforehand.
• Overcut corners. The blade cuts past the corner of the opening and weakens the panel for no reason. Drilling the corners or finishing them by hand prevents this.
• Dry cutting in an occupied flat. Fine concrete dust gets everywhere and is harmful to health. Wet cutting, or extraction with a suitable filter, is essential.
• Unsupported blocks. A heavy cut-out piece can damage the floor or injure someone if it falls in one go.
• Ignoring the neighbours. Cutting is loud. Let the neighbours know in advance and follow the building's house rules.

Before you accept the work, look at the opening in good light with a spirit level in hand. For a load-bearing wall, it helps to have the structural engineer or a site supervisor there for the handover.

• The opening matches the agreed size and leaves room for the door or window frame
• The edges are plumb and level, checked with a spirit level
• Cuts from both sides meet without a step and there are no overcuts at the corners
• There are no new cracks or broken-off pieces in the panel around the opening
• The steel strengthening is installed as the structural engineer specified
• Nearby services are undamaged and working
• Slurry and dust have been cleaned up and the floor and furniture are undamaged
• The waste has been removed and you have the structural design and any documents the building authority requires