How to Replace Cast Iron Pipes With PVC

PVC pipe can be used to replace old damaged cast iron pipes throughout your home.

Older homes used cast iron for plumbing pipes because the material was strong enough to handle the pressurized water often flowing through the systems while being fairly resistant to deterioration. Over time, the cast iron pipes may begin to develop leaks. Rather than replace with more cast iron or another metallic pipe, an easy replacement fix is to use polyvinyl chloride pipe (PVC) instead. All that’s needed is the properly sized coupling between old pipe and new and the correct PVC connecting procedure.

Things You'll Need

• Safety goggles
• 5-gallon bucket
• Black marker
• Tape measure
• Reciprocal saw with diamond-tip blade
• PVC pipes
• Utility knife
• Rubber transition gaskets
• Flat-head screwdriver

Instructions

1. Cut the flow of water to the pipes you intend to replace from the main cutoff in your home. Locate the nearest drain for the pipe and drain as much of the water within the pipe as you can into a 5-gallon bucket, emptying the bucket as necessary.

2. Locate the pipe you wish to replace and place marks on the pipe with a black marker on both sides of the damaged area. Measure the length of the marked area with a tape measure to determine the length of PVC pipe needed as a replacement.

3. Cut through the cast iron pipe at the marked points using a reciprocal saw with a diamond-tip saw blade. Always keep the body of the saw above the pipe to avoid having water spill from the pipe into the saw’s components. Pull away the cut portion of the pipe.

4. Purchase PVC pipes sized to fit the cast iron pipes. Cut the PVC pipe to match the measured length of the removed cast iron pipe. Scrape the pipe ends on both the inside and outside with a utility knife to remove any plastic burrs.

5. Cover both ends of the cast iron pipes with rubber transition gaskets by slipping the ends of the gaskets over the ends of the pipes halfway down the gaskets' length.

6. Place the PVC pipe ends into the other ends of the rubber gaskets attached to the cast iron pipes. You can bend the gaskets and PVC pipes slightly to perform the fitting.

7. Tighten the gaskets into place over the cast iron pipes by tightening the screws holding the metal band around the base of the gaskets. Tighten the other ends of the gaskets around the PVC pipes using the same process.

8. Turn the water back on. Watch the newly joined pipes and feel for leaks. If a leak occurs, turn the water back off and tighten the gaskets further.

Tips & Warnings

• Replace an entire cast iron pipe by making your cuts through the pipe joined with the cast iron pipe, including the pipe coupling, and then attaching a PVC coupling and pipe instead.

• Wear safety goggles when cutting the pipes to avoid injury from pipe slivers.

References

• Pipe Gripes: Replace Old Cast Iron Sewer Pipes with PVC
• Plumbing Help: Replacing Old Metal Drainage Pipes
• Creative Homeowner: Tying into Old Cast Iron