Slab Leak Found. Now: Spot Repair, Reroute, or Tunnel?

Once we have pinpointed a slab leak with the acoustic gear and the pressure tests, the conversation turns to how to fix it. There are three approaches, and we use all of them. Which one is right depends on where the leak is, what the pipe is made of, what is on top of the floor, and whether this is the first leak or the third.

Option one: break through the slab and repair the spot

The direct approach. We cut a section of the slab over the leak, expose the pipe, replace the failed section, and pour the concrete back. The floor covering over that area is removed and has to be replaced afterwards.

It works well when the leak is in an accessible spot, the floor covering is something replaceable such as carpet or a tile you can still match, and the rest of the pipe is in good condition. It is the fastest way to have the water back on. It is a poor choice when the leak is under a kitchen island, a shower or an expensive floor, and it does nothing about the rest of the line.

Option two: reroute the line overhead

Instead of repairing the pipe under the slab, we abandon that run and install a new line through the attic and down the walls to the fixtures it served. Nothing in the floor is touched. The old pipe stays in place, capped off and dry.

This is the approach we recommend most often in Rowlett, Garland and the older parts of Rockwall, where the houses are on the original copper and the leak is the result of decades of clay soil movement working the pipe. A spot repair on a pipe like that fixes one point on a line that will fail at another point in a few years. A reroute retires the whole run. It also means a small amount of drywall repair at the drops rather than a hole in the floor.

The trade-off is that overhead lines in a North Texas attic need to be insulated properly and routed away from the roof deck, because an attic is both very hot in summer and the first place to freeze in winter.

Option three: tunnel under the slab

A crew excavates from outside the foundation, tunnelling beneath the slab to reach the pipe from below. The repair is made and the tunnel is backfilled. The floor and the interior of the house are untouched.

Tunnelling makes sense when the leak is under something that cannot be disturbed and a reroute is not practical, most often on a drain line rather than a supply line, since drains cannot be rerouted overhead. It is the most labor-intensive of the three and takes longest, and on a slab that has been repaired or piered before it needs coordination with whoever did that work.

How we decide, in practice

• Supply leak, first occurrence, accessible location, replaceable floor: spot repair.
• Supply leak, second or later occurrence, or under a kitchen or bath: reroute.
• Drain leak under the slab: tunnel, or spot repair if it is near an exterior wall.
• Widespread pinholing or a house already on its third leak: whole-house repipe, which retires every line at once.

What happens to the foundation

Homeowners worry that cutting the slab or tunnelling under it will weaken the foundation. Done properly, neither does. A slab cut is patched with concrete tied to the existing slab; a tunnel is backfilled and compacted. The larger foundation risk is the leak itself: water under a slab in expansive clay swells the soil unevenly, which is what heaves floors and cracks walls. Getting the water stopped is what protects the foundation, and that argues for acting quickly rather than for any particular method.

Family-owned in Rockwall, licensed and insured, with Rowlett and Dallas County on our daily routes. TX Master Plumber TXM11693. (469) 338-5533.