how to protect and prevent rusting outer sewer line

Old 10-07-23, 01:42 PM
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how to protect and prevent rusting outer sewer line


I went inside my crawl space today to remove a mouse I finally caught with the trap.
I noticed that my sewer line that exists my house have heavy rust and corrosion (see picture).
The vertical pipe (galvanized?) is coming from the bathroom on the first and second floor and the horizontal pipe (copper?) is the sewer line for the kitchen and our master bathroom.
We do get some water coming into our crawl space when we have very heavy rains so I'm guessing that's what caused this rust outside the sewer line.
What is the best measure to add protection and prevent or slow down the rust in the arrow area?
Would you recommend spraying Rust-Oleum cold galvanizing compound spray paint?
Just wondering what are the options to add layer of protection from getting in contact with water and rusting.
Thank you.

Old 10-07-23, 02:01 PM
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Welcome to the forums.

It would take a lot of rust to damage those cast iron fittings
It would also be hard to re-coat all the way around it.

I wouldn't worry about the rust.
I would try to control the water there... if possible.
Old 10-07-23, 08:31 PM
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Thanks Pete.
I am a bit worry about the rust because I can actually scrap off bunch of rusts with my bare hands...
I didn't realize that's cast iron fitting but wouldn't it be better to spray or paint something that either seals from water touching/penetration and/or prevent/slow down the rust than not do anything?
Yes, I do need to control the water from coming into my crawl space but I've been putting it off since water comes in only few times a year during heavy rains for consecutive days.... I do monitor my crawlspace when it rains heavily then pump out any water and run dehumidifier to control humidity..
Old 10-08-23, 04:48 AM
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At this point I don't think it's worth the effort to try and protect the cast iron. Don't forget, the line is possibly cast iron all the way to the sewer main so where do you stop painting? Since the rust is worst on the male side of the connection it's also possible that the connection has a slight leak.
Old 10-08-23, 09:46 AM
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I think rust on the outside of cast pipes is quite common. Pipes generally fail due to corrosion beginning from within, not on their outer surfaces. Rust often forms on the underside of cast iron pipes.

Cast iron pipes under little or no pressure typically do not actively leak. Still, rust is usually a sign that internal corrosion has breached the pipe walls and is normal after about 25 years. The good news is cast iron 'waste drain' pipes will usually last anywhere between 50 and 100 years.
Old 10-17-23, 09:58 AM
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I'm going to the dissenting voice here... from the one picture, it looks like you might have a crack developing, and the rust doesn't look great. If it's not leaking, it'll last another 5-10 years, but IMO, it's on its way out.

Good news is that it won't one day fail. It'll start dripping slowly, then get a bit worse... so you'll have warning and can plan to replace when needed. Once it starts leaking, you'll have easily a year or two to replace it. It's not like a pressurized pipe that's going to 'burst' one day.

The bad news is there's not much you can do about it now. Cleaning it and coating it with a JBWeld or something might get you an extra few months, but it won't help much. Painting it won't help either.

The good news is cast iron 'waste drain' pipes will usually last anywhere between 50 and 100 years.
Based on the galvanized coming into it and the condition of the wye, I'd put it at ~80 years old. At least that's how a lot of houses look around here at that age.

As long as the pipe going out is still solid, it's not a bad repair. But will need to be done somewhat soon.

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