How to Splice a Cast to PVC


Cast iron pipe rusts from the inside out and becomes brittle over time. PVC plastic pipe is among the most common pipe materials used fordrainage, waste and vents. Fernco couplings are rubber boot couplings that fit over existing cast iron pipe, allowing you to adapt the cast iron pipe to PVC. Some local building code enforcement agencies require a licensed plumber to repair and replace cast iron pipe, especially if the cast iron pipe is tied in with municipal drain lines. Fernco couplings, PVC pipe and PVC fittings are available at local home improvement and plumbing supply stores.

Things You'll Need

  • Fernco couplings
  • Tape measure
  • PVC fittings
  • PVC pipe
  • PVC primer
  • PVC glue
  • Marker
  • White chalk
  • Chain pipe cutter
  • Angle grinder
  • Screwdriver
  • No hub torque wrench
  • Silicone caulk
  • Pipe hanger strap
  • Hold a Fernco coupling tight to the hub of a PVC wye or tee fitting and measure the distance between the Fernco hub and the PVC hub with a tape measure. Whether you use a wye or tee fitting depends on where you'll splice the PVC to the cast iron.

  • Cut two lengths of PVC pipe with a PVC handsaw using the measurement taken and prime and glue the lengths into the PVC fitting with PVC primer and heavy duty PVC glue.

  • Measure the length of the PVC fitting and pipe from end to opposite end and add 1/4-inch to the measurement. This allows the PVC pipe and fitting to fit between the two cast pipe ends.

  • Measure and mark the cast iron pipe with a marker or white chalk where the PVC it to be spliced.

  • Cut the cast iron pipe with chain pipe cutters or an angle grinder and remove the section of cast iron pipe.

  • Slide a Fernco coupling completely over both open ends of the cast iron pipe.

  • Place the PVC fitting into the cast iron pipe and slide the Fernco couplings over the ends of the PVC pipe. The Fernco couplings should cover the PVC and cast iron pipe equally.

  • Tighten the metal bands on the Fernco couplings evenly with a screwdriver or No Hub torque wrench, tighten the torque wrench until it clicks. There are two metal bands on each coupling.

  • Apply a bead of silicone caulk to the edges of the Fernco couplings where the couplings meet the PVC and cast iron piping.

  • Fasten pipe hanger straps as close to the Fernco couplings as possible; this will keep the couplings from sagging.

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