Slab Leaks

for your information:  Slab Leaks

Once detected, be it through high water bills, dampness or wetness on the floor, water coming through the foundation or the settling of the foundation, must be found. Slab leaks occur in two places, either the incoming water line or the sanitary sewer line both of which are imbedded in the foundation of your home. (see Ground Plumbing for more information) Both types of leaks can cause a large amount of damage to the foundation and each source of leaks has its own probable causes..

Slab leaks in the incoming water line are often more destructive as the water is under pressure, the main water line from city runs under the slab and comes up beside the water heater where branches of copper piping go from one area of the house to another supplying hot and cold water to each fixture…Pinhole leaks can occur anywhere along this copper tubing which goes to every fixture in your house. Some common causes are:

  • Shifting of the foundation due to poor design and installation, or drought, causing the piping to move with it , pull apart and begin to leak
  • Water Chemistry – If the water has a certain chemical combination ie. high pH, high suspended solids, low organic matter, aluminum bearing compounds, and free-chloride water, the addition of a water softener can cause a leak in the pipes
  • Electrolysis – All metals have stored energy, based on the energy it took to refine the ore. When different metals come into contact and electric current will flow between to equalize energy stored. If copper pipes and the steel rebar are in contact the resulting electric current will cause pinhole leaks in the copper pipes in your foundation. ( see Corrosion and Maggnesium Anodes for more information on this subject )
  • Water Velocity – If the the water velocity or flow rate is too high for the copper piping used, erosion can occur in the protective coating, creating areas of bare uncoated copper, and a high rate of corrosion. In addition leaks will form at any change of direction or bend in the copper piping as a result of high water velocity.
  • Poor Workmanship evidenced by excessive use of flex, poor soldering, not reaming or kinking the copper can result in leaks in your incoming water lines .

click here for more information on Detecting Water Line Leaks

Slab leaks in the sanitary sewer line only leak when one of the fixtures in your home is used, like flushing a toilet or running a faucet, some common causes are:

  • Shifting of the Foundation – Cast iron and PVC are brittle and will crack and brake with too much shifting of the surrounding foundation
  • Poor Workmanship- Pipes need to be cut straight and true, as an angled cut will not seal properly, each fitting must be secured to the pipe properly with solvent weld, pushed all the way into the fitting and held until the glue sets. Skipping any step causes failure of the joint.
  • Rust – When piping is left in soil that is constantly wet, dissolved minerals such as sulfate and chloride along with large quantities of organic material will act upon the cast iron or galvanized pipe causing breakdown and failure. PVC can be immersed with no effect.
  • Chemicals, solvents, cleaning solutions which we all put down our drains causes break down to occur sooner in cast iron piping than in PVC piping.

Any foundation leak can cause big trouble! Determining the source of a slab leak is an educated technical process of elimination.Your foundation or slab is monolithic, meaning in one piece, and is all tied together with rebar or steel to the beams and piers before the concrete is poured. Embedded in that concrete is the preparatory ground plumbing (click for details) which includes all the pipes that bring water to all your fixtures from the city water system or your well and the sanitary lines that take the waste water out of your home from each fixture. If done properly, most foundations have a fill layer of sand beneath them placed over the existing subsoil. Water seeks the course of least resistance and the lowest spot, and so the water leak travels in that sand layer away from the original site of the leak making locating the source of the leak all the more difficult. If one section of the foundation is compromised by a leak, the whole foundation may be compromised. As the leak goes on undetected, and more water is absorbed by the soil around and under the slab, several dynamics can occur :

  1. Erosion: Where the leak literally washes out the supporting soil
  2. Consolidation of localized pockets of subsoil that produces differential movement
  3. Auto-compaction : the physical removal of supporting contact between soft surface and slab