If you’re buying a home built before 1970 there’s a good chance your drain
waste system is made of cast iron. Opinions vary about the functionality and
durability of cast iron. You’ll have to separate fact from fiction, shut out the noise,
and make a smart decision about your future or existing home.
Cast iron plumbing has been in use for hundreds of years because it’s so
durable, and because it also does a great job of insulating noisy running
water. So why the bad rap? It’s all in the chemistry.
When cast iron pipes carry waste hydrogen sulfide gasses are created. When
these gasses oxidize, corrosive sulfuric acid is created, rusting the pipes from the
inside out. The rust flakes within the pipe can gather in one location and restrict
the flow of water: slow drainage is often the first indication of a problem, and
homeowners may find themselves calling the plumber every six months to clear
out the pipe.
If the pipes are located below the slab inspecting them will be difficult. Hire an
experienced, licensed plumber to insert a Borescope into the drain to view the
interior of the pipe.
If the home is built on piers and beams spot repairs can be tempting. Why not
just replace the few feet of pipe where the problem is? This isn’t recommended.
It’s difficult to get a licensed professional to warranty their work unless all of the
antiquated pipes are replaced. Spot repairs to the pipes can expose the
foundation system (if they leak again) to excessive, undetected moisture which
could cause unwanted settlement.
So keep cast iron piping or cast it out? Older cast iron waste pipes should be
judged on a case-by-case basis. First hire an experienced home inspector to
collect information about the drain waste system’s performance. Ask your home
inspector to do a visual inspection of the pipes if possible. If your inspector is any
good at all he to she will flood test several sinks and tubs to identify slow
But slow drainage can be related to other problems and may not indicate
damaged cast iron pipes, so your second step is to hire a licensed professional
plumber to evaluate the interior and when possible the exterior of the pipes.
Failure to replace or line the damaged pipes may result in more headaches down
Know the facts, know your home, and know your options. And don’t get it
checked, get it double-checked.