This was recommended to us- old pipes are rusty and leaky.
Cast iron pipes will last for many years, but they will eventually rust out from the inside out. The use of caustic chemicals to open clogs can accelerate the process. We work on many older homes with cast iron pipes. I never suggest that they be changed just because they are cast iron. I do recommend that they be cleaned out annually to remove built up crud.. I have seen 3" pipes that have not been maintained have only 1" of effective drainage due to build-up. If your pipes are rusting through, or cracked and leaking, it will be wise to change them out. If they are rusted through in some areas the rest is sure to follow. It will cost more in the long run to keep patching then until they totally fail.
Changing over these pipes to fix leaks is fine. Just understand that there are some drawbacks to PVC. The primary one is not using the correct pipe for the job. The PVC pipes you purchase at the big box stores Schedule 40 is ok, for small jobs. But if your changing a main sewer pipe going through the home, you want to purchase a heavy duty PVC Schedule 80 which is thicker. Primary reason is noise. One benefit of cast pipe is that is silences the noise when the water runs through it. The Schedule 40 pipe is noisy. While the thicker 80 works like the cast pipe and keeps the water noise down. While this may not sound real important. You have not been in a new home eating dinner in dining room when someone flushes a toilet on the second floor. Everyone hears it. Cast pipes over time begin to flake off in sections inside the pipe. Quite often you can see this result by seeing tiny rust dots or stains on the outside of the pipe. Once this begins the pipe is more prone to plugging as the interior of the pipe becomes rough and catches paper as its flushed down. When changing them, particularly when the cast runs up the wall, be sure to support these pipes when you remove the damaged section that is lower or below. A lot of weight is combined with these pipes and they can crack easily within the wall if the drop down because of poor support
I HAVE A VERY SMALL LEAK. BUT ONLY WHEN I FLUSH MY FIRST FLOOR TOILET. A SMALL AMMOUNT OF WATER LEAKS ONTO THE BASEMENT FLOOR. I BELIEVE THIS IS THE OUTGOING WATER, WASTE ETC.. THAT GOES OUT THE MAIN 5 INCH PIPES. THE ACTUAL HOLEE IS 1 INCH BY 2 INCHES. THE PIPE ITSELF IS VERY OLD. I ASKED A PLUMBER, BUT HE CANNOT BE TRUSTED. I KNOW THIS. HE SAID THAT ITS A $5000.00 DOLLAR JOB. I KNOW THAT IS NOT TRUE. I ALSO DO MUCH PLUMBING MYSELF ALTHOUGH I AM NOT A PLUMBER. I HAVE CHANGED A GARBAGE DISPOSAL, NO PROBLEM, INSTALLED NEW FAUCETS, NO PROBLEM, AND PUT ALL NEW COPPER PIPES MYSELF. NO PROBLEM. BUT THIS AT THE MAIN SHUT OFF .AROUND NEAR THE GOOSENMECK AND COMPANION WITH PLASTIC COVER. THIS IS IMPORTANT. I DON,T WANT TO MAKE IT WORSE. AND I , AT THIS TIME DO NOT HAVE THE FUNDS TO HAVE A PLUMBER DO IT. AND THATS A FACT. I AM PAYING SKY ROCKETING HOSPITAL AND DOCTOR BILLS. OR TRYING TO ANYWAY. I WAS DIAGNOSED WITH LIVER CANCER 4 WEEKS AGO. CAN ANYONE HELP? THANK YOU IN ADVANCE FOR JUST READING THIS.
I have seen a lot of issues with cast iron plumbing recently. I know it's a pretty common material in the plumbing of older houses, and even some newer ones, though it's rare. If I were you, I would replace it with PVC, as you're much less likely to get cracks, leaks, or rot in plastic. But if you aren't having any issues, there may be other ways to keep the cast iron plumbing if you'd like; Alon above mentioned wrapping them in fiberglass mats and resin, which sounds pretty smart. Hope you get it sorted! http://www.goldcoastplumber.com.au/