Leak Under a Concrete Floor? Find It Through the Slab

Many houses built after the war, and most extensions since, have a solid concrete ground floor. Heating pipes were laid straight into the screed, sometimes in copper with no sleeve, and the cold supply pipe was often run under the hall floor. Decades of contact with cement and damp slowly corrode copper, and ground movement strains the joints. When a pipe in a screed fails, the water has nowhere to go but into the concrete and the ground below. The first signs are often a boiler losing pressure, a bill that has risen, or a floor that feels warm or damp in one place.

Finding a leak under concrete is a matter of using methods that read through the slab. The acoustic ground microphone picks up the sound a pressurised leak makes as water forces its way through the concrete and the ground. We move it across the floor in a grid and the reading peaks over the leak. For heating pipes, the thermal imaging camera shows the warm line of the pipe run and the spread of heat where hot water is escaping. The exact route to open is visible before any tools come out. A moisture meter confirms how far the water has travelled under the finish.

Where the pipe is plastic, deep, or too quiet to hear, we drain it and introduce a hydrogen and nitrogen tracer gas. Hydrogen is the lightest gas there is and rises through screed, concrete and floor coverings. The Variotec detector finds where it surfaces. This is a leak detection method and has nothing to do with gas safety. Nitrogen pressure tests on each circuit tell us which pipe to concentrate on. Underfloor heating loops can be isolated at the manifold one at a time, so the leaking loop is identified before the floor is touched.

Once the leak is pinpointed we mark the slab, photograph the location and write it into the report with the readings and thermal images. If you want the repair done, we cut one small opening by hand at the mark and expose the pipe. We repair it in copper or barrier pipe and leave the opening ready for making good. Trace and access cover on most buildings policies pays for locating the leak and reinstating the floor. Escape of water cover deals with the damage the water has caused. We keep those costs separate in the report and will speak to the claims handler if that helps.