Almost never the whole floor. A leak under a concrete slab is located from above using tracer gas, acoustic listening and thermal imaging, then one small access hole is opened at the confirmed spot. Where you have trace and access cover, most buildings policies pay to make good that hole afterwards.
You have a damp patch on a solid floor, or a meter that will not stop turning, and someone has said the words “it must be under the concrete”. Your mind goes straight to a breaker, a skip on the drive and a kitchen out of action for a fortnight. So let us answer it properly: no, in most cases you do not have to dig up the floor to find the leak. Any digging happens after the leak has been found, and it is small.
Why the floor is the last thing we open
Water under a slab does not stay where it escaped. It follows the fall of the concrete, tracks along the pipe duct or the damp-proof membrane, and surfaces wherever it finds a weak point in the screed. The wet patch you can see is a symptom, not a location. Break up the floor at the wet patch and you are guessing, often by a metre or more.
That is why underground water leak detection works in the opposite order. First confirm there is a leak. Then narrow it to a pipe run. Then narrow it to a point. Only then does anyone pick up a tool. If you already have the symptom and want to know what it means, our guide to a wet patch on a solid concrete floor covers the early checks.
Step one: prove the leak before anyone touches the slab
If your home is on a water meter, the meter is your best witness. Turn off every tap and appliance, note the reading, and leave it for an hour with nothing running. If the numbers or the small flow indicator have moved, water is escaping somewhere. Then close the internal stopcock and repeat. If the meter stops, the leak is on your side of the stopcock, which for a solid floor usually means a supply pipe buried in or under the slab. If it keeps moving, the leak is on the buried supply between the boundary and the house.
Heating pipes tell a different story. A sealed heating system with a slab leak loses pressure, so the boiler gauge drifts down and needs topping up, and the damp patch may feel slightly warm. That points us at the heating circuit rather than the cold mains.
How the leak is pinpointed through concrete
Three methods do most of the work, and we usually combine them because each one sees something the others miss.
Tracer gas
The pipe is drained and a safe mix of hydrogen and nitrogen is introduced under gentle pressure. Hydrogen is the smallest molecule there is. It escapes at the leak, rises straight up through screed, concrete, tiles and carpet, and a hand-held detector picks it up at the surface. Because it rises almost vertically, the strongest reading sits directly above the fault. This is the method that gives the most confident result on plastic pipe, which makes very little noise when it leaks.
Acoustic listening
Water escaping a pressurised pipe hisses. A ground microphone amplifies that sound through the slab, and the reading peaks over the leak. On longer runs, a correlator with two sensors clamped at either end of the pipe works out the position from the difference in the time the sound takes to reach each one. Copper carries sound well, so acoustic work is often the quickest route on older pipework.
Thermal imaging and moisture mapping
A thermal camera shows temperature differences on the floor surface. A leaking hot pipe leaves a warm plume, a cold mains leak leaves a cool one, and the shape of that plume tells us which way the water is travelling. A calibrated moisture meter then maps how far the damp has spread and where it is heaviest. Neither finds the leak on its own, but together they rule out large areas in minutes and tell us where to concentrate the gas or the microphone.
| Method | Best for | What it cannot do |
|---|---|---|
| Tracer gas | Plastic pipe, pinhole leaks, deep or well-insulated runs | Needs the pipe drained and isolated first |
| Acoustic | Copper and steel, mains-pressure leaks, long supply runs | Struggles with quiet leaks on plastic or under very thick slabs |
| Thermal | Heating and hot water pipes, mapping the spread of damp | Sees the surface effect, not the pipe itself |
What the access hole actually looks like
Once the location is marked, the opening is typically a square of a few hundred millimetres, cut with a disc cutter so the edges are clean, then broken out with a small breaker down to the pipe. On a screeded floor with a plastic duct, the pipe often sits just below the surface and the hole is shallower still. The repair is made and tested, then the hole is backfilled and screeded ready for the floor finish to go back.
Compare that with lifting an entire floor covering and breaking out a strip along the suspected run. A single located hole means one repair, one tile to match, and a room back in use in days rather than weeks.
Some leaks avoid the floor altogether. If the damaged pipe runs from one accessible point to another, it can be cheaper to abandon the buried section and re-route a new pipe around the edge of the room. We tell you when that is the better option.
Cornish floors and why they matter
Cornwall’s housing is a mixture that keeps us on our toes. A modern estate house in Truro or Newquay sits on a poured slab with the supply pipe in a duct through the concrete, and tracer gas works beautifully. A granite or cob cottage near Bodmin might have had a solid floor poured over the original earth floor decades ago, with a copper pipe laid directly in the screed and no drawings anywhere. Extensions often mean a suspended timber floor on one side of a wall and concrete on the other, with the pipe crossing between them.
Our soft, slightly acidic water is gentle on kettles but not on copper. Pinholing in copper laid directly in screed is something we see regularly in the county, particularly where the pipe had no protective sleeve. A pinhole is exactly what tracer gas finds well.
Will the insurer pay to make good the hole?
This is where the fear of the floor usually eases. Most UK buildings policies include trace and access cover, which pays for the cost of finding the leak and for putting right the damage caused by getting to it, including cutting into and reinstating a concrete floor. The limit is often somewhere in the £5,000 to £10,000 range. What the cover does not do is pay to repair the failed pipe itself, and the resulting water damage to the room is normally a separate escape of water claim.
We write our survey up as a report that names the method used, shows the readings and thermal images, and marks the exact position of the leak, because that is what the insurer wants to see before authorising the reinstatement. If you have not claimed before, our guide to what trace and access insurance actually pays for explains the wording, and a plumber who could not find the leak is a common reason people come to us with a claim already open.
What to do before the survey
- Do not dry the patch out. Heaters and dehumidifiers on the wet area make the moisture map harder to read. Ventilate the room, but leave the floor alone.
- Do not lift or cut the floor. A neat, undisturbed floor gives clean thermal and acoustic readings.
- Find the stopcock and the meter. We will need both. If the meter is out at the lane on a long Cornish supply run, tell us so we allow time.
- Note the boiler pressure. Photograph the gauge morning and evening for a couple of days if you suspect a heating leak.
- Tell your insurer. Log the claim before any work so the trace and access element is agreed from the start.
We provide leak detection across Cornwall, and a survey on a solid floor is usually a single visit.
Frequently asked questions
How do you find a water leak under a concrete floor without breaking it up?
We confirm the leak with a meter or pressure test, then locate it from the surface. Tracer gas introduced into the drained pipe rises through the slab above the fault, a ground microphone hears water escaping under pressure, and a thermal camera shows the plume. The floor is only opened at the confirmed point.
How big is the hole you have to make in the floor?
Usually a neat square of a few hundred millimetres, cut with a disc cutter and broken out down to the pipe. On a screeded floor with a shallow duct it can be smaller. Once the pipe is repaired and tested, the hole is backfilled and screeded so the floor finish can be reinstated.
Can you find a leak under tiles or laminate?
Yes. Tracer gas and acoustic readings pass through tiles, laminate, carpet and vinyl, and thermal imaging reads the surface temperature whatever it is made of. We do ask that you leave the covering in place, because an undisturbed floor gives cleaner readings than one that has been partly lifted.
Does insurance cover cutting into a concrete floor to reach a leak?
Most UK buildings policies include trace and access cover, which pays to locate the leak and to reinstate the damage caused by reaching it, including a concrete floor. Limits are often in the £5,000 to £10,000 range. The repair to the failed pipe itself is not covered, so check your own wording.
Is it better to re-route the pipe than to dig?
Sometimes. If the leaking section runs between two accessible points, a new pipe above ground or around the room can be quicker and cheaper than breaking out and reinstating the floor. We tell you at the survey which option makes sense for your floor, your pipe and your insurer.
Find it first, then open one spot
If you suspect a leak under a solid floor anywhere in Cornwall, we will locate it from the surface and mark the exact point before anyone breaks concrete. You get a clear, insurance-ready report to support your trace and access claim.
