Chasing Channels for Water Installation (Concrete)

Good work starts before any machine is switched on. The tradesperson first works out where the outlets for taps, the WC, the washing machine and the kitchen sink will go. From that, they plan the shortest route with as few bends and joints as possible.

1. Turn off and drain the water in the affected part of the home if work is near existing pipes.
2. Scan for hidden services with a detector and compare the results with any drawings, especially for electrical cables, gas and heating pipes.
3. Mark the routes on the wall with a pencil, spirit level or laser, keeping to vertical and horizontal lines only.
4. Cover the floor and furniture with plastic sheeting, seal the doors and set up dust extraction.
5. Cut two parallel lines to the required depth with a wall chaser.
6. Break out the strip of concrete between them with a light breaker or a chisel.
7. Clean out the chase, check its depth and width and remove any loose pieces.

The plumber then lays the pipe in insulating sleeves, fixes it in place and carries out a pressure test before anything is covered. Only once the system holds pressure is the chase filled with cement mortar or a suitable repair compound.

In concrete, the usual tool today is a wall chaser with two diamond blades. It cuts accurately, the depth is set in advance and, with a vacuum connected, it produces much less dust. The wall does not take unnecessary blows, so the surrounding plaster and concrete stay sound.

Cutting by hand with a hammer and chisel, or with a breaker and no pre-cut lines, makes sense only where the chaser will not fit: in corners, behind risers or next to door frames. It is slow, the chase tends to be wider and uneven, and a larger chunk of material often comes away around it and has to be filled.

Why does this matter? A narrow, straight chase is quick to fill, uses little mortar and leaves no bumps under the tiles. A wall that has been broken up has to be repaired over a much larger area.

In many blocks of flats, especially those built from precast concrete panels, most walls and all floor slabs are reinforced concrete. Many internal walls are load-bearing, and the steel reinforcement often sits only a few centimetres below the surface. A deeper chase can easily hit it, and cut reinforcement weakens a panel that also carries the flats above you.

• Only cut into load-bearing walls after a structural engineer has assessed them. Be especially careful with horizontal chases, which weaken a load-bearing wall more than vertical ones.
• Water chases are not cut into ceilings or floor slabs.
• Tell the building management or owners' association before work starts. They often have their own rules for alterations to the structure and for noisy work at certain hours.
• Check with your local building authority whether work on a load-bearing structure needs approval under local building regulations. Do not assume that a simple notification is enough.

If the route through a load-bearing wall cannot be avoided, a common solution is a false wall made of plasterboard or a frame installation system, where the pipes run without any cutting. In a bathroom this is often handy anyway, because a wall-hung WC frame fits inside it.

How demanding the job is, and therefore what it costs, depends on a few things you can look at in advance:

• Wall material: ordinary concrete cuts more easily than hard reinforced concrete with dense steel
• Length and number of chases: every outlet and every branch means another cut and more breaking out
• Depth: larger pipe with insulation needs a deeper and wider chase
• Access: a small bathroom, corners, work around a riser or a furnished home all slow the work down
• Empty rooms: in a home without furniture and old tiles the work is quicker and cleaner
• Unknown services: without drawings, tracing cables and other pipes takes more time

In practice, chases are often cut diagonally to make the route shorter. A few years later someone drills into that wall to put up a shelf and hits the pipe. Vertical and horizontal routes are easy to predict even without a plan.

Another mistake is a chase that is too shallow. The pipe then sticks out, the plaster over it cracks, and cold water pipes can cause condensation. A chase that is too deep weakens the wall for no reason and, in a concrete panel, reaches the reinforcement. A depth of roughly 3 to 5 cm and a width of about 4 to 6 cm are often quoted, but the size always depends on the diameter of the pipe with its insulation and on the wall material.

It is also common for pipes to be covered without a pressure test and without photos. A leaking joint under tiles means breaking open a finished wall. Hot water pipes are best laid in a sleeve so the pipe can move slightly as it heats and cools, which keeps the plaster from cracking.

Finally, safety. Concrete dust contains silica and harms the lungs. Use an FFP2 or FFP3 respirator, safety glasses, ear protection and dust extraction. If a gas pipe is damaged during the work, stop immediately, do not use electrical switches, appliances or naked flames, open the windows, leave the property and call the gas emergency number for your area or 112. Any repair must be done by a qualified, registered gas engineer. If an electrical cable is hit, switch off the circuit breaker and call an electrician.

Before the chases are filled, go through a few points with the tradesperson:

• Chases run only vertically and horizontally along the agreed route
• Depth and width suit the pipe with insulation, and the pipe does not stand proud of the wall anywhere
• The edges of the chases are straight and the surrounding plaster is not loose
• No electrical cable, gas pipe or heating pipe has been damaged
• The structural engineer's advice has been followed in load-bearing walls
• The pipe is fixed, sleeved and has passed a pressure test
• There are photos of the routes showing distances from corners and the floor
• The chases are filled solidly and flush with the surface, ready for plaster or tiles