Many older homes today were plumbed with cast iron drain pipe before PVC drain pipe was available. Consequently, some of those older drain pipes have begun rusting and need to be repaired. If any part of your drain pipes are cast iron and are rusted, you can repair the rusted section, rather than replacing the entire pipe. Here are 5 steps that will help you accomplish this without creating an expensive replacement project.
Step 1 – Locate a Section of Solid Pipe
Locate a section of pipe that is not rusted. Rust is not always visible on the surface of the pipe. At times, the pipe is rusting beneath a painted surface, so don't assume that because a painted section of pipe doesn't show rust, there is no rust there. If you see paint blisters on the surface, try to peel some of this blistering away and examine the metal beneath the paint for the appearance of rust. Choose a section of good, solid pipe at both ends of the rusted section.
Step 2 – Cut Out the Rusted Pipe Section
Use a reciprocating saw with a metal cutting blade and cut the rusted piece out of the cast iron pipe. Have a helper hold the rusted section in place while you cut, otherwise when the saw severs the old pipe at both ends the pipe is likely to drop. Be sure the power receptacle into which the saw is connected has a GFI (Ground Fault Interrupter) that will handle a short if water from the cut pipe should drain into your saw while you are cutting. Keep in mind that this drain pipe will probably have water and black sludge in it that is likely to drain down onto you and your saw when you open the bottom pipe surface. When you have cut through both ends of the rusted pipe, remove the pipe.
Step 3 – Replace Rusted Pipe with PVC Pipe
Instead of trying to find more cast iron piping to replace the rusted section, connect PVC plastic piping to fill the gap. Measure the space you've cut out of the cast iron pipe, then cut a piece of PVC drain pipe (schedule 40) that will fit snugly into this space. Clean both ends of the new PVC pipe with PVC cleaner, and let the cleaner dry. Be sure you have fittings in place on the pipe, apply PVC glue to the fittings, place the PVC pipe piece into the space from which you removed your rusted pipe, and join the sections. You will need a helper to hold one end of cut iron pipe while you're making the second cut. You'll also need him to hold one end of the PVC pipe while you are connecting the pieces at the other end.
Step 4 – Check and Adjust Fittings
Before the glue has set, check your pipe and fittings to be sure they are all straight and in place. Twist the pipe as you bring the pieces together. This will help seal the joints better.
Step 5 - Connect Joints
Connect joints with a no-hub connector, a rubber connector around which is a steel band with two stainless steel clamps, each with a nut you can use to tighten the clamp.