August 13, 2009
Since its inception, PVC (DWV) pipe has been the most widely used material for sewer lines. PVC is lightweight, easy to use and resilient. When properly installed, PVC will provide unprecedented years of use and is impervious to root penetration.
Defects found in PVC sewer lines are usually attributed to poor planning or poor workmanship. Applications where ground movement is frequent or severe, PVC may not be suitable and cast iron may be required. Common problems found in PVC applications are typically due to poor installation.
A properly installed PVC sewer line begins with the excavation of a gradually sloped trench. Once excavated, the slope of the trench is corrected using cushion sand or fine sandy loam that is tamped and compacted. The pvc pipe is then installed sloping no less than 1/16th of an inch per linear foot (slope rates differ based upon the size of the pipe). Failure to properly bed the pipe can result in low spots in the pipe itself also known as “bellies”. These low spots will allow sewage to collect and may create drainage problems.
PVC pipe is joined through a chemical process known as solvent welding. A properly installed PVC joint consists of a precisely measured portion of pipe (the pipe is measured to butt flush into the hub of the joint) squarely cut and properly de-burred, and a fitting of similar construction both of which have been properly cleaned with primer and cemented. Any single step, not properly exercised, may cause problems.
Poor craftsmanship can result in weak joints that may separate. An improperly bedded sewer line may cause undue stress on fittings causing them to break. PVC pipe that has not been cut squarely will result in a weak joint which is more susceptible to failure. Furthermore, if the pipe fails to butt flush into the hub, it may create a void where solids can accumulate. It is not uncommon for these poorly constructed joints to break or splinter should a sewer cable catch the edge of the pipe exposed by the void.
Roots should not be an issue in a properly installed PVC sewer line. Stoppages are mainly attributed to abuse or unusual situations. Should stoppages occur frequently, the line should be inspected for defects.