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Concrete Slab Leaks

By: Howard Powell
AMCO Plumbing Service, LLC

History

Many homes built in Southern Nevada and throughout the Southwest, from the mid 70’s through 1999, were constructed on concrete slab foundations. During construction, soft rolled copper water lines were placed in the soil just below the concrete slab floor. Building codes at the time did not permit the use of hard rigid copper, as rigid copper is produced in 10 and 20 foot lengths and no joints, soldered or otherwise were allowed beneath the concrete slab. As a result, only long lengths of soft rolled copper, which is pliable, could be installed. Soft copper, which is easily bent, was rolled out in the soil from fixture to fixture and bent up through the concrete slab. The generally accepted method of installation was to begin at the water meter and roll the soft copper to the shut off valve in the front yard. From there it was rolled out to the water heater location which was generally in the garage and then it would be stubbed up through the concrete and looped from fixture to fixture. At the water heater location, a manifold was installed and both a hot and cold water line were looped throughout the house in the soil from fixture to fixture and left sticking up out of the ground and the new concrete slab was poured over the soft copper. After the house was framed by carpenters, plumbers would install “type M” hard copper piping in the walls and connect it to the soft rolled copper protruding from the slab.
When we refer to concrete slab leaks, it is the soft rolled copper pipe in the soil below the concrete, not actually embedded in the slab of concrete. The copper protruding though the concrete at each fixture location is sleeved in light weight plastic, which is red or blue in color, to designate the hot or cold water line.

Facts

The Copper Institute and the copper manufacturers state that hard copper will last at least 50 years. However, several factors affect soft rolled copper much more aggressively. Conditions that affect the natural processes of pipe deterioration internally are friction, pressure, chemical and abrasive action. Hard mineralized or acidic water with a pH of 7 or less can be very hard on soft copper pipes and, in conjunction with friction and pressure, may result in copper corrosion or pitting. During the construction process, rolled copper is laid out on the ground, just beneath where the concrete slab will be poured. Many other tradesmen are working on top of the copper after installation. Concrete crews install a steel rebar mat directly over the copper which is pulled into the concrete during the pour to reinforce the concrete. This is often the cause of bent, kinked or impinged soft copper.
Erosion corrosion, also known as impingement damage is the combined effect of erosion and corrosion caused by rapidly flowing water under pressure. It is the second most common cause of copper tube failure behind copper corrosion and pitting. Any nicks, kinks, bends or impingements will eventually wear through due to erosion from the rapidly flowing water.
The abrasive action of chemicals and minerals results in internal pipe wall thinning and pitting and will subsequently lead to failure and leaks under the concrete slab. Leaks will generally present on the hot water line due to expansion and contraction of the metal. These leaks normally take about 12 years to develop, but once they begin to leak, the entire pipe is dangerously thin and spot repairs are not the answer. The so-called slab leak, which is actually an underground water leak could typically be discovered by one or all of these indicators, an increased water or gas bill, a hot spot on the floor, a damp or wet area on the floor, hearing running water with all fixtures turned off, running out of hot water quickly or low water pressure at one or more fixtures. Once a slab leak is detected, it must be addressed. Slab leaks are on pressurized water lines and the leak will continue to grow in size discharging large volumes of water into the subsoil causing erosion and possibly settling and cracking of the concrete slab. If water service providers detect an unexplained large increase in water volume usage they will lock off the City meter until appropriate repairs have been made.

Direct Repair

Several repair methods can be employed to correct under-slab water leaks. First, we must locate the leak within 2 feet of the source and determine if it is the hot or cold water line. The most economical method is the direct approach. This requires the removal of the floor covering, i.e. wood, carpet, tile, cabinets and whatever else is in the way. Next, a jack hammer is used to remove approximately 2 feet square of the concrete slab. Once the concrete slab is opened, all standing water is then pumped out and the soil is removed to expose the leaking copper pipe. After the spot repair is completed the concrete must be replaced and all floor covering and other items removed must be restored. This method is a temporary fix and additional leaks on the dangerously thin copper normally develop in a different location, some within months of the original repair due to the increase in pressure. After the first jack hammer repair home owners generally seek a more permanent solution.

Bypass

The next most common method of repair is to bypass only the leaking copper line from its point of origin to its termination point and cut-off the copper to that fixture just above the concrete slab. This method requires cutting out drywall on walls or ceilings and installing a new water line in the walls, ceiling or attic above the floor. This method is a partial fix as it leaves soft copper remaining under the concrete which can rupture again at any time.

Repiping

This method is a permanent fix to the slab leak problem as all soft copper piping under the concrete slab is completely abandoned. This method also requires removing small sections of drywall at several fixture locations and possibly some ceiling locations to install all new hot and cold water lines. Starting at the water heater location and continuing throughout the residence, new hot and cold water lines are installed within the wall and ceiling cavities as necessary to provide a new hot and cold service feed to a fixture or group of fixtures. This method normally requires several days to complete as the drywall must be replaced, taped, textured and repainted after the repiping is completed.