Crack in a cast iron drain pipe: fix it or replace it?

A crack in a cast iron drain pipe will not heal, and it usually gets longer. A small crack can be held with a stainless sleeve, but cast iron that has cracked has often rusted thin everywhere, so a sleeve buys time more than it fixes the pipe. The permanent fixes are cutting out the cracked section or lining it. This page sits under our guide to drain vents and slow drains, because a cracked stack often shows up first as a slow drain or a smell.

How do I know the crack is in the cast iron and not somewhere else?

Look for the crack's effects, not the crack. Stains, rust weeps or damp drywall along a stack, a sewer smell that comes and goes, gurgling after a flush, or a wet patch on a garage or crawl space floor all point to a leak in a drain line. A camera or a dye test then shows exactly where.

Cast iron fails in a few typical ways. It rusts from the inside, building scale that narrows the bore and makes drains slow. It rusts through at the bottom of horizontal runs where water sits. And it cracks at a hub or a bend when the house shifts or something heavy hits it.

Three quick checks you can do safely:

• Tap the pipe with a screwdriver handle. A dull thud or flaking rust means thin metal. A ring means sound metal.
• Run a hand light along every exposed run in the garage, crawl space and under sinks.
• Pour a bucket of water into the highest fixture on the stack and watch the lower runs for a drip.

If the crack is below a slab or inside a wall, you cannot see it. A sewer camera inspection is the way to find it.

Can I fix a cracked cast iron drain pipe myself?

You can seal a small, clean crack in an exposed run yourself, and many people do. A stainless repair sleeve with a rubber gasket, or a fiberglass wrap, will stop a drip. It is a temporary repair on a drain that carries no pressure, and it will not stop a long crack from running.

Here is what the repair options look like side by side. The lifespans are rough ranges from published repair guides, not promises.

Before any of these, support the pipe above and below the repair. Cast iron stacks are heavy, and cutting one without hangers in place can drop a whole run.

How do you fix a leaking cast iron drain pipe for good?

The lasting fix is to cut out the damaged length and replace it with new pipe joined by no-hub couplings, or to line the pipe from the inside. Cutting out a section is the usual answer when the crack is in a stretch you can reach. Lining suits long runs where opening walls would cost more than the repair.

Cutting cast iron is its own job. A snap cutter, a chain tool with cutting wheels, is the standard way to get a clean, square cut. Our page on how to cut cast iron drain pipe covers the method and why a grinder is the second choice.

The replacement material is typically plastic, joined to the old iron with shielded transition couplings. Check the rating on each coupling for the job, because a coupling meant for a vent will not do on a buried drain.

In Los Angeles, plumbing work inside a house needs a permit, and work on the sewer lateral outside it can need another. Our sewer line repair page explains the permits and who may do the work. In California, general engineering, plumbing, sanitation system and pipeline contractors may install or repair building sewers, according to the state contractors board.

How long does cast iron drain pipe last?

Cast iron drain pipe is usually quoted at 50 to 100 years, and the real figure depends on the water and the soil around it. Hard water scale builds inside, and wet soil, leaking joints and old repairs rust it from outside. A cracked pipe in a house from the middle of the last century is often near the end.

That is why one crack deserves a wider look. If a camera shows scale and pitting along the rest of the run, patching the crack is spending money on a pipe that will fail again within a few years. If the camera shows a single injury in otherwise sound metal, a sleeve or a section swap makes sense.

Signs that the whole run is worn out:

• More than one leak on the same stack
• Flaking, layered rust on the outside
• Slow drains that return days after cleaning
• A camera showing a rough, narrowed bore

For what a full swap costs, see cast iron drain pipe replacement cost.

What should I do first when I find a crack?

Stop running water to the affected line if the crack is leaking into a wall or floor, and mop up so the damage does not spread. Then photograph the crack, note where it is, and get the line looked at before you choose a repair. A cheap sleeve on the wrong problem costs more than a short inspection.

If the leak is on a line that carries toilet waste, treat the area as unclean. Wear gloves, ventilate, and keep children and pets out. If sewage reached drywall or insulation, that material usually has to come out. Our guide to cleaning up a sewer backup covers that side.

When the crack is on the part of the line outside the house, the owner is responsible for it, according to Los Angeles County Public Works, for the entire length of the lateral, including the stretch under the sidewalk or street.

Should I call a plumber, and what will they do?

Call one when the crack is below a slab, inside a wall, on a stack that serves several floors, or on a line outside the house. Those jobs need a camera, a permit and the right couplings. A plumber will normally camera the line, mark the defect, and give you a written price for sleeve, section swap, lining or replacement.

You can send a quote request and we'll arrange a visit from a local drain cleaner. You get a written price before any work starts, and nothing is done until you agree. The rest of our services are on the LA Drain Works home page.

Questions people ask

How do you repair a crack in a cast iron drain pipe?

For a small crack on an exposed run, clean off the rust, fit a stainless sleeve with a rubber gasket or apply a fiberglass wrap, and test with water. For a longer crack, cut out the section and replace it with new pipe and no-hub couplings. Support the pipe above and below first, or the run can drop.

Is epoxy good enough for a cracked cast iron drain?

Epoxy is a short-term patch. It can seal a pinhole on a drain that carries no pressure, but it adds no strength and will not stop a linear crack from spreading. Published guides put its life at anywhere from a few months to several years. Treat it as a way to buy time while you plan a proper repair.

Is a cracked cast iron pipe an emergency?

It is urgent when it leaks sewage into a wall, a floor or a crawl space, because the damage and the smell grow every day. It is less urgent when it is a hairline crack in an exposed run that is not wet. Either way, plan the repair soon, because cracks tend to lengthen over time.

Can a cracked cast iron pipe be lined instead of replaced?

Often yes, when the pipe is still in place and round. A resin liner is pulled through and cured against the old wall, which seals cracks and joints from the inside. It suits long or buried runs. Heavily collapsed or badly offset pipe may need replacing first. See sewer pipe lining.

Will home insurance pay for a cracked drain pipe?

Policies differ, and wear and tear is commonly excluded, while sudden damage sometimes is covered. Read your policy or ask your insurer before you start repairs, and keep photos and quotes. Our page on sewer line insurance explains how the common endorsements work.