Replacing a section of cast iron pipe is easier than you think.
Step 1: Cast-iron pipe is very heavy. Before cutting out a section of pipe, secure the plumbing stack or run in place. Wrap rebar tie wire or metal pipe strap above the section of pipe to be cut. Use nails or screws to secure each end of the wire or strap to a nearby joist or header board.
When securing a vertical stack, wrap the wire or strap below a hub or an elbowed section of the pipe to keep the pipe from slipping down.
Step 2: A reciprocating saw with a carbide blade or an angle grinder with a diamond blade will both cut cast-iron pipe, as will a chisel and a hammer. A ratcheting soil pipe cutter is by far the easiest tool to use to cut through cast-iron pipe. Soil pipe cutters can be rented from your local hardware store or rental center.
Step 3: Read the manufacturer’s instructions completely before using the soil pipe cutter.
Step 4: Choose a smooth section of the pipe to cut, preferably 4 inches or more from any hub or joint. Make sure the pipe is free of dirt and debris. Use a stiff wire brush to remove any loose rust.
Step 5: Wrap the cutting chain around the pipe and lock the chain into place per the manufacturer’s instructions.
Step 6: Once the chain is secure and the cutter’s knobs are adjusted properly, use a slow and steady motion to ratchet the chain tight around the cast-iron pipe. As the chain is tightened, the cutting wheels will squeeze into the pipe and the pipe will snap beneath the pressure.
Step 7: Remove as large of a section of the old pipe as possible and replace it with a similar sized piece of PVC pipe.
Step 8: Use rubber couplings with adjustable metal clamps to attach the new section of PVC pipe to each open end of the cast-iron pipe. Fernco makes rubber couplings in several sizes to fit just about any situation. Rubbing a few drops of dish soap on the inside of the couplings will make them slide onto the pipe easier.
Step 9: Once the couplings are in place, tighten the metal clamps. Put away your tools and move on to your next project