Leaking under a basement sink

[jodieleigh]

Help! Trying to sell my home quick! Noticed a slow steady seepage of water at the base of the hot water supply line coming up through the concrete floor into a basement sink. How do I repair this quickly?[?]

[LazyPup]

It would be very difficult to suggest how to fix the problem without having some additional information.

First of all, if the pipe is a synthetic material (PVC or CPVC) it is doubtful that the pipe is really leaking. In this case it would most likely be ground water under the slab leaching up through the concrete between the edges of the concrete and the pipe wall. In this case you might be able to stop the leak by applying a sealer around the pipe.

If it is a metal pipe such as galvanized iron, brass or copper pipe the problem is most likely resulting from the pipe having by now severely corroded from chemical action between the lime in the concrete and the pipe metal. For this reason the plumbing codes now prohibit any direct contact between concrete and metal pipes. (The Electrical codes also prohibit direct contact between concrete and electrical conduits.) Once a pipe has corroded enough to cause a leak their is a very high risk that even the slightest mechanical stress on the pipe will cause it to break right off at the floor.

Whenever a plumbing pipe is passed through concrete we are required to sleeve the pipe, which means we first install a piece of PVC pipe 2 sizes larger than the desired pipe and extending out at least one inch on either side of the concrete. The desired pipe is then passed through the sleeve and the space between the inner wall of the sleeve and the desired pipe is filled with expansion foam.

In the electrical trade they normally use PVC concrete below grade and transition to metal conduit slightly above the finished floor, or in instances when they must pass a metal conduit through the concrete it is wrapped with PVC tape or sleeved with PVC.

If this is a metal pipe in direct contact with the concrete, while the leak is only apparent at the floor level it is almost a foregone conclusion the the entire section of the pipe in the concrete is by now porous from corrosion.

The only proper way to fix the pipe would be to break out the concrete so you could gain access to the pipe below the level of the concrete. (A basement floor is typically about 4" thick ). Once you are through the concrete you would need to dig a few inches into the dirt under the concrete and make the repair, stubbing s new section of pipe up through the floor.

If it is an older house with galvanized iron pipes you will most likely find a threaded 90 deg elbow slightly below the floor level where you could unscrew the pipe and screw in a new piece of pipe.

If it is copper pipe you would need to cut the pipe and weld a new section on. Notice I stated "weld" rather than "Solder". The plumbing codes prohibit any mechanical joints (Threads or compression fittings) or solder joints below a slab. When running copper under a slab we are required to use wrought copper or hardened bronze fittings and they must be brazed instead of soldering. Normally in new construction all copper lines under slab are run with seamless roll copper pipe.

Once you have the repair made and a new section of pipe stubbed up above the floor, you should then slip a piece of PVC pipe over the stub up, making sure the bottom end of the pipe is in the dirt under the slab and the top end of the PVC should extend about 1 inch above the finished floor, then you can poar concrete in the hole to repair the floor. Sackrete concrete mix is excellant for repairing the concrete. When the concrete has had time to set you then fill the gap between the PVC sleeve and your new pipe with expansion foam.