Chasing for Gas Pipework (Brickwork)

A good chase starts before anyone switches on a tool. On site, the work usually goes like this:

1. Marking out the route. Following the design or the gas engineer's instructions, the route goes onto the wall with its exact height, branches and connection points for each appliance.
2. Checking the wall. A cable and pipe detector, plus any drawings available, show whether electrics, water or heating pipes run along the route. If an old gas pipe is nearby, the gas engineer must isolate it and make it safe first.
3. Preparing the room. Furniture goes out or under dust sheets, floors get cardboard or protective sheeting, and doors to other rooms are sealed against dust.
4. Cutting the edges. A wall chaser with two diamond blades cuts two parallel lines at the set width and depth. This gives straight edges and stops the surrounding plaster from breaking away.
5. Removing the middle. A breaker or SDS hammer with a flat chisel takes out the material between the cuts.
6. Cleaning and checking. Dust and loose pieces come out of the chase, and the depth, width and straightness are checked. Only then can the gas engineer lay the pipe.

Hand chasing without a machine is mostly used in corners, near the ceiling or around obstacles where the chaser cannot reach. It is slower and the result is less precise.

It looks like the same job, but the wall material decides the tools, the time and the risks.

Brickwork

Solid fired brick chases fairly well. Perforated or hollow blocks, common in newer houses, need more care: the thin walls of the cavities break easily and the chase can suddenly widen. That is why it pays to cut first and chisel second, rather than knocking the chase out with a hammer alone. In older houses the brick is often brittle and the mortar weak, so the work has to be gentler.

Concrete and reinforced concrete

Concrete is much harder. The work is slower, dustier and louder, and without diamond blades it is hardly possible. Most concrete walls also contain steel reinforcement. Nobody should cut through it without a structural engineer's approval, because it weakens the load-bearing structure. In blocks of flats built from concrete panels, chasing load-bearing walls is often restricted, especially horizontal chases. Before chasing concrete in a block of flats, talk to the building management or owners' association, and to a structural engineer if the wall is load-bearing.

A chase is cut for a specific pipe. It should be slightly deeper and wider than the pipe, so the pipe sits without strain, can be fixed with clips and then covered with mortar and plaster. The gas engineer sets the exact size based on the pipe type and diameter. A chase that is deeper than needed weakens the wall, particularly in load-bearing walls and close to windows and doors.

Gas pipes in walls run only horizontally or vertically, never at an angle. Why does this matter? If someone drills a shelf a few years later, they can guess where the pipe runs from the position of the valve or appliance. With a diagonal route, nobody can.

The gas pipe must keep a safe distance from electrical cables, water pipes and other services, as set out in the design, the relevant EN standards and your national gas regulations. Valves and screwed or other removable joints must never be buried in the wall; they have to stay accessible. Many countries also have specific rules on burying gas pipes in walls, for example sleeving or a protective wrap so the pipe is not set solid in the material. Your gas engineer will know what applies where you live.

How demanding the chasing is, and so what it ends up costing, depends on a few things:

• Wall material: concrete and reinforced concrete take far more effort than brick
• Length and shape of the route: a straight run along one wall is simpler than a route with many bends and passes through walls
• Access: working near the ceiling, in corners, behind kitchen units or in a furnished home takes longer
• Surface: if tiles or thick plaster have to come off first, there is extra work
• Clean-up: dust extraction, removing rubble and making good the chases are often agreed separately

An empty room and a clearly marked route save time for everyone. In a block of flats, it is good manners to warn the neighbours in advance, because chasing is loud.

• A diagonal route, or one that simply follows "whatever was easiest", which the inspecting engineer will not accept
• A chase that is too shallow, so the pipe has too little cover and the plaster above it cracks
• A chase that is too deep in a load-bearing wall, cut without asking a structural engineer
• Cut reinforcement in reinforced concrete
• A damaged cable or pipe, because nobody checked the wall before cutting
• Chasing with an angle grinder only, which creates a lot of dust and leaves an uneven depth
• A dirty chase, where clips and mortar do not hold well and sharp edges can damage the pipe

Cutting the chase itself usually needs no special qualification. Installing, connecting, pressure testing and checking the gas pipework, however, may only be done by a qualified, registered gas engineer. So the chases are always cut in agreement with the gas engineer, never "blind" in advance.

Whether your alterations need a notification or a permit depends mainly on whether load-bearing walls are affected and whether the gas installation changes. Do not assume it is fine without asking: check with your local building authority. In a flat, always inform the building management or owners' association as well, because load-bearing walls and shared services do not belong to you alone.

If you smell gas during the work, stop immediately, do not switch any electrical devices on or off, open the windows, leave the property and call your gas emergency number or 112.

Before the gas engineer lays the pipe and the chases are filled, go through these points:

• The route matches the design or the agreement with the gas engineer
• Chases run only horizontally and vertically
• Depth and width are even along the whole length
• Edges are straight and the surrounding plaster is not needlessly broken
• No reinforcement is cut in concrete and no large cavities are broken open in brick
• No other service has been damaged
• Chases are clean of dust and debris
• Rubble is removed and the room is cleaned as agreed
• After the pipe is installed, a pressure test is done and the gas engineer issues a test certificate or safety record