Pipe grouting and no dig repair

Which buried pipes can be repaired without digging

The dividing line is bore. Anything an engineer can get a camera and a packer inside can usually be repaired from within, and that means drainage and other gravity pipework from roughly 100mm upward, whether it is clay, pitch fibre, cast iron or plastic. Below that size there is nothing to work through, so a 15mm or 22mm copper heating pipe in screed and a 25mm or 32mm supply pipe under a drive cannot be lined or grouted at all. Anyone offering to line a domestic water pipe is describing something else.

That does not mean those leaks need a trench across the garden. A supply pipe is replaced rather than repaired, and it can be replaced by driving a new one through the ground from a small pit at each end. A leaking pipe buried in a solid floor inside the house is usually better abandoned and rerouted along an accessible path than chased out of the slab. In both cases the point is the same: the surface stays intact because the work happens below it or around it.

• Drainage under floors, driveways and gardens, sealed or relined from an existing chamber or access point
• Joints and hairline cracks in buried drainage sealed with injected resin grout
• Voids washed out under a slab or a drive filled with grout so the ground stops moving
• Root intrusion and intruding connections cut back with a robotic cutter, then sealed
• External water supply pipes replaced by impact moling or directional drilling, with a pit at each end
• Buried supply and heating pipework rerouted through an accessible run instead of opening a floor

What resin grouting actually does

Grouting is a sealing repair. A packer is winched into the pipe on a camera and positioned across the defect, then inflated so it seals against the pipe wall either side of it. A two part gel, normally an acrylate, is pumped into the space between the packer and the pipe, forced out through the open joint or crack, and pushed into the ground immediately around the pipe. It cures in a few minutes into a collar of set gel bonded to the soil and the outside of the pipe, and the packer is deflated and withdrawn. The bore is left clear.

What that fixes is water passing through the pipe wall in either direction: groundwater getting in and raising the flow, or foul water weeping out and washing the ground away. It is very effective on displaced or open joints in old clay drains, which is the single most common defect under a London garden, and on fine cracking that has not moved.

What it does not do is give the pipe strength back. A grouted joint is a seal, not a structure. Grout will not bridge a missing section, it will not hold a pipe that has lost its round shape, and it will not stop a pipe cracking again if the reason it cracked is that the ground under it is still settling. If someone grouts a defect without establishing why the defect happened, the same repair will be needed again.

The other job grout does is filling voids. A leak that has run for months under a slab or a block paved drive washes fines out of the ground and leaves a hollow. Seal the pipe and leave the hollow and the surface above it keeps dropping, which is how a drive ends up dipping a year after a repair that worked. Where a survey shows a void, filling it matters as much as sealing the pipe.

Grouting is only as good as the survey behind it. A defect that is sealed without the camera footage to show what the pipe looks like either side of it is a guess with resin on it.

Patch lining or a full length liner: which one a drain needs

Where the pipe itself has failed rather than just leaked at a joint, the repair is a liner. A patch liner is a glass fibre mat impregnated with silicate or epoxy resin, wrapped around an inflatable packer and winched into position under the camera. The packer is inflated, which presses the resin soaked mat hard against the pipe wall and squeezes it into the crack, and it is held there while the resin cures. The packer comes out and what is left is a new bonded wall over the damaged length, usually around a metre, a few millimetres thick and effectively a pipe inside the pipe.

A full length liner, the cured in place method, does the same thing over a whole run between two chambers. A felt tube is impregnated with resin, either inverted into the pipe under air or water pressure or winched in and inflated, and cured with hot water, steam or ultraviolet light depending on the liner. It takes the shape of the existing pipe including the bends, and once cured the branches are reopened from the inside with a robotic cutter.

Full lining is the standard answer to pitch fibre, which was used widely in post war London drainage and fails in a recognisable way. It softens, delaminates into layers and deforms from round into an oval, usually worst where a drive runs over it. Patching one spot in a pitch fibre run is wasted work because the whole length is at the same age and in the same condition.

Lining loses a small amount of bore, a few millimetres of wall thickness. On a 100mm foul drain that is irrelevant to how it runs. On smaller pipework, or on a run that was already flat and marginal for fall, it is worth a conversation before committing, because a liner is permanent.

Replacing a supply pipe without digging up the drive

A leaking or undersized water main from the boundary to the house is a replacement job, and there are three ways to do it without a trench. Impact moling launches a pneumatic hammer head from a small pit and drives it through the ground on a set line, towing the new blue MDPE pipe behind it. Directional drilling uses a steerable head tracked from the surface, so the bore can be aimed around known services and brought up exactly where it is wanted. Pipe bursting pulls the new pipe along the existing route while a bursting head splits the old pipe outward into the surrounding ground, which is the option when the old line is the only sensible path.

In practice that means two openings: one near the boundary and the external stopcock, one where the pipe enters the property. Everything between them, block paving, tarmac, lawn or a mature bed, is left alone. Moling needs ground that will take it, so it is ruled out by heavy made ground full of brick rubble, by a route congested with other services, and sometimes by what the survey finds in the first few metres.

The old lead, steel or black alkathene pipe is normally left in the ground, dead and disconnected. That is standard practice and it is worth knowing rather than discovering later. A replacement is also the moment to get the pipe to a sensible diameter and a proper depth, because an undersized or shallow supply is the reason behind a lot of poor flow and frozen pipe calls that get blamed on the boiler. A supply pipe that has split outright rather than weeped is a burst pipe repair and a different order of work, because the water has to be stopped at the stopcock before anybody surveys anything.

Leaks under a solid floor inside the house

Inside the property the no dig techniques above do not apply, because nothing in a domestic hot, cold or heating circuit is big enough to work inside. The realistic choices are to pinpoint the leak and open a small, defined area, or to abandon the buried run and reroute it.

Rerouting is often the better value decision and it is not the one people expect to be offered. Copper laid in screed that has pinholed once has usually been sitting in the same aggressive conditions along its whole length, so the next failure tends to arrive nearby within a couple of years, and each one means opening the same floor again. Running a new leg in a boxed corner, behind the kitchen units, through the ceiling void of the floor below or under a lifted section of a timber floor costs a single disruption instead of a repeating one, and leaves pipework that can be seen and isolated.

Where the floor does have to be opened, the opening should be the size of the repair and no larger, which is what the detection stage is for. That part of the work is leak detection and repair rather than drainage, and the acoustic, thermal and tracer gas equipment it uses is what keeps the opening down to one board or one patch of screed. Cutting exploratory holes across a room because the damp patch is vague is not a method.

Why a CCTV drain survey comes before any repair

For drainage the survey is a CCTV inspection with a self levelling head and a sonde, run from an existing chamber or a rodding eye. The sonde lets the position and depth of a defect be traced and marked on the surface, and the operator logs each defect with its distance from the chamber, so the report describes a specific point rather than a general condition. A dye or water test confirms which run is which where the layout is not obvious, and that matters in a converted house where two flats share a stack.

The footage is what decides between grouting, a patch, a full liner and excavation. A pipe that is cracked but still round takes a liner well. A pipe that has deformed, dropped at a joint into a step, or lost a section will not accept one, and forcing a liner into it produces a repair that fails at the same point. You are entitled to see the recording rather than a summary of it.

For a suspected supply leak the survey is different: isolate at the stopcock and watch the meter, pressure test the section, then use acoustic listening and tracer gas to place the loss along the route. That tells you whether you are replacing the external main or chasing something inside the building, and those are two completely different jobs.

When digging is still the right answer

A good engineer will tell you when the trenchless option is the wrong one. A collapsed pipe, a missing length, a severe deformation, an open joint with a big step in it, or a run that needs a new connection or a new fitting all mean excavation, because there is nothing sound left to line or seal against. So does a drain that keeps failing in the same place because of ground movement, tree roots at the source or a badly made original connection, since lining over that only postpones it.

There are also cases where digging is simply the lighter option. A shallow pipe under a lawn or a gravel path is quicker and less disruptive to expose and replace than it is to survey, clean, line and reinstate, and pretending otherwise to sell a technique is not a service. The honest test is which method leaves the property in a better state for longer, not which one sounds cleverer.

Before any of this, if water is escaping now, close the stopcock and isolate the electricity to any area where water is near a fitting or a socket. Our page on what to do first when water is escaping sets out that order, and an emergency plumber visit comes before a survey rather than after it. Survey work starts once the property is safe.

What the ground looks like after a no dig repair

Reinstatement after no dig work is small because the openings are small. Pits are backfilled and compacted in layers rather than tipped back in, which is what stops a drive dipping over the following winter. Block paving is lifted whole and relaid. Tarmac and concrete are patched, and a patch in either of those will be visible, so that gets said before the work starts rather than at the end. Chambers are left with sound benching and a correctly bedded cover.

Internally, where a floor or a wall has been opened to reach a pipe, boards go back fixed rather than loose, screed is made up and plasterboard is patched and set ready for decoration. Structure that is genuinely wet has to dry before it is closed permanently, because sealing damp in produces mould and lifted flooring months later.

You should finish with a record: the pre works footage, the post works footage of the lined or grouted section, and the position and depth of anything that was repaired. If there is an insurance claim, that is what the insurer asks for. If the property is sold, it is what the buyer's surveyor asks for. It is far easier to hand over than to reconstruct from memory two years on.

The claim and the ownership question

Trenchless work is planned work. It is surveyed, quoted and booked, and it happens after the property is already safe. Water escaping in the house right now is a different sequence entirely and is dealt with by isolating the supply first, so nothing on this page should delay that.

Once the ground is settled, two questions usually decide who pays. The first is the policy. What your insurer means by trace and access is the part of a buildings policy that covers locating a leak and getting to it, as distinct from the repair itself, and no-dig methods tend to sit well with it because the access cost is genuinely low. Read the wording rather than assume, because the definition varies between insurers and some will only pay against a survey that names the defect and its distance from the chamber. That is exactly what a logged CCTV report gives you.

The second is ownership, and in a converted building it is rarely obvious. A stack or a lateral shared with the flat upstairs is not usually the same responsibility as a branch serving only your rooms, which is why who is responsible for a leak in a leasehold flat is a question for the lease and the managing agent rather than for the engineer holding the camera. What we can do is trace the defect, record where it sits relative to the boundary and the chamber, and hand you something factual to argue from. Getting that established before the repair is booked saves the awkward conversation about who commissioned the work.