Cast-iron pipes can be difficult to work with, but with our help, you'll feel confident in your repairs.

January 26, 2019

To extend or repair cast-iron drainpipe, make the transition to PVC drainpipe. Several types of no-hub fittings are available to join iron and plastic; check local codes to see which are accepted. A no-hub fitting has a neoprene sleeve and clamps that are tightened around the cast-iron pipe and the plastic piece to hold them in place and make a watertight joint. Such fittings are considered a permanent joint.

Cast-iron pipe is heavy, so work carefully and use a helper. Support pipe with clamps and framing before cutting it. Add clamps above and below the new joint or leave the frame permanently in place. If you're confident in your handy skills, follow along with our steps below as we show you how to install a fitting onto a cast-iron drain pipe. 

What You Need

  • Carpentry tools
  • Cast-iron snap cutter or circular saw with metal-cutting blade
  • Felt-tip marker
  • PVC saw or backsaw and miter box or power miter saw
  • Deburring tool
  • Hex screwdriver or torque wrench
  • Riser clamps
  • Plastic pipe or fitting matching cast-iron pipe
  • Banded couplings

Step 1: Steady Pipe

Secure the pipe above and below the point that will be cut so that neither end can fall or move sideways while you work. To be safe build a frame like the one shown here and attach the pipe to it with riser clamps.

Step 2: Cut Pipe

Next to a snap cutter, the quickest way to cut cast iron is with a circular saw equipped with a metal-cutting blade. Wear eye and ear protection. If a circular saw will not reach all the way around, cut all or part with a reciprocating saw equipped with a metal-cutting blade.

Step 3: Prep Pipes

To install a tee or Y, glue two short pieces of pipe to each end of the fitting, making sure the resulting component will fit snugly between the pipes. Slip the no-hub fitting onto each of the cast-iron pipe ends.

Step 4: Install Fitting

Position the fitting or replacement piece between the two cut cast-iron ends and pull the neoprene sleeve over the plastic.

Step 5: Tighten Sleeve

At each joint, slide the neoprene sleeve of the no-hub fitting so it's centered on the joint. Tighten the band nuts using a hex screwdriver. Some codes may require the use of a torque wrench, which will stop tightening when you reach the proper band tightness.

Installing a Saddle-Tee Drain Fitting

Step 1: Cut Hole

If it's approved by your local inspector, a saddle fitting is easier and quicker to install. Cut a roughly circular hole in the cast-iron pipe using a grinder equipped with a metal-cutting blade. The hole should be slightly larger than the opening in the fitting.

Step 2: Neoprene Sheet

Hold a neoprene sheet for the fitting against the hole and trace the outline of the hole. Cut a hole in the sheet that's slightly larger than the hole in the pipe. Squeeze silicone sealant around the hole.

Step 3: Install Saddle-Tee

Position the sheet over the hole and press the plastic fitting over it. Slip a U-clamp around the back of the pipe and slide its threaded ends through the plastic fitting. Screw on the two nuts finger-tight. Attach the other clamp the same way, then tighten all four nuts.


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