Under Slab Plumbing Repair
So now that the plumbing system has been proven to leak, what next? A thorough repair plan should be made in direct correlation with the plumbing leak testing report. If the piping under your foundation is comprised of cast-iron, it’s most likely time to replace your sanitary system with PVC. If the cast-iron system is not replaced, there is a high likelihood that the leak or leaks will continue to get worse. The two most common methods to repair under slab sanitary piping are tunneling under the foundation and breaking through the concrete slab.
Tunneling Under The Slab
Depending on the area of the leak, tunneling may be a cheaper option. For example, if the area where a leak exist is near the perimeter of the foundation, it may be easiest to tunnel under the grade beam for quick access as opposed to breaking through the foundation and creating a mess. The main reason tunneling is utilized for access is to replace entire cast-iron under slab plumbing systems when other methods of access are not an option.
Repairing or replacing under slab sanitary piping by tunneling starts by excavating an access hole near the perimeter of the foundation. After digging the access hole well below the bottom of the perimeter concrete grade beam, the excavation then turns horizontal and proceeds under the foundation. The path and size of the tunnel is configured to allow plumbers to enter and replace the sanitary piping, either leaving it in the original location or rerouting it out from under the footprint of the residence and trenching a new line to connect to the city sewer main or building sewer.
The original sanitary piping is usually cut several inches beneath the bottom of the concrete slab and the new sanitary piping is connected using heavy duty couplers. The new piping must then be hung from the slab to prevent future displacement. After the new piping is installed and properly supported, a hydrostatic test is performed to insure that all of the leaks have been repaired. Finally, the tunnel is ready to be backfilled.
Backfilling the tunnel must be done in such a way as to prevent damaging the new piping. In addition, backfilling of the tunnel should be done in a way that limits the potential for the causing future foundation movement. Backfilling consist of putting back the same soil excavated from beneath the foundation and from within the access hole; hauling off the soil excavated and not utilized. The primary advantages of making under slab piping repairs by tunneling are avoiding the indoor mess associated with construction activities and the opportunity to replace large sections of older, less desirable cast-iron piping. Another advantage sometimes realized in choosing to tunnel instead of break through the floor is saving the expense of replacing damaged floor coverings. The main disadvantage of making under slab piping repairs by tunneling is the high cost. The high costs are a direct result of the intense labor associated with the hand excavating, transporting and backfilling large amounts of soil.
Breaking Through The Slab
Breaking through concrete slabs to modify, repair or replace sanitary piping is a substitute for tunneling in order to save in repair cost. If the flooring will need to be replaced anyways, it’s a great time to get your foundation fixed. Repairing or replacing under slab sanitary piping by removing and replacing concrete begins by accurately locating the piping and the leaks. If possible, carpeting or other flooring is removed for later re-installation and attempts are made to control the messy construction activities. A 3X3 hole is made through the foundation for access to the leak. After the plumbing repairs are completed, a hydro test is performed before covering the work and patching the slab.
The primary advantage of making repairs to the under slab sanitary piping by breaking through the floor instead of tunneling is the enormous cost saving that can be realized in some instances. The cost savings are directly related to the amount of expensive tunneling avoided. The disadvantages of this repair method include the high level of accuracy required in pin-pointing the leaks, the indoor mess associated with construction activities, and the inability to replace large sections of piping as a preventative measure as can be done with tunneling.