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Cast Iron, and the Slow Loss of Bore

In short

Cast iron corrodes along the invert — the bottom of the pipe, where the flow sits — and the scale it leaves catches everything passing. What presents as a blockage on such a run is often lost bore, which is why clearing it works for a while and then stops working.

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Cast iron is the lateral material that fails least dramatically and gets diagnosed latest, because nothing about it goes wrong on a particular day.

Corrosion runs along the bottom

Waste sits in the invert — the bottom of the pipe — longer than anywhere else, so that is where cast iron corrodes. The metal channels, and scale builds up standing proud of the surface. The result is a pipe with less cross-section than it was laid with, and a rough interior that catches what passes.

Why it reads as a blockage

Everything a homeowner notices — slow drainage, gurgling, a line that needs clearing again — looks like something stuck in the pipe. On cast iron it usually is not. The capacity has gone, and material collects because there is less room for it. Clearing buys time proportional to how much bore is left.

What to ask a contractor

Ask what the bottom of the pipe looks like, and ask them to show you. Ask whether the house side or the yard side is worse, because cast iron was commonly used on the house side with another material beyond the boundary, and the two sections do not fail together.

Why the price can surprise you

A quote for lost bore is not a quote to remove a blockage; there is no blockage. It is a quote to restore capacity, which means lining or replacing a length. If a slow drain comes back priced like major work, this is normally the reason, and the recording will show it — what a survey should show you.

More on the material: cast iron laterals.

Get the run looked at

Tell us your ZIP code and what the drain is doing. We check it against partner coverage and put you through to an independent contractor who works that area. We do not do the work and you are never charged.

Call (866) 857-3202

Before anybody excavates.A camera survey is a different instruction from a repair, and the order matters. Tell us what the drain is doing and we will route you to somebody who covers your area. No charge to you, ever. Anything else the plumbing is doing can be raised on that call too.

Call (866) 857-3202