doechsli

My house was built in the late 50's and has cast iron pipes for the main stack. I have replaced everything but the stack and what is under the basement floor with PVC. I have always kept paint on the exposed portions of the pipe but I have two places that quickly corrode through the paint. Is there any way to repair this to prevent the corrosion from spreading?

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Dennis

nealtw

Cast iron rust is like a scab that protects it from rusting more.

ozone

As mentioned above, rust is a natural occurance for cast iron that is not a problem. If your issue with it is appearance then you could try a product/chemical called "ospho". I have used it many times in the past with great results. Brush or spray it on, (windex type spray bottle will do), let it sit over-night and the rust becomes a hard black paintable substance. I've even used it prior to painting a rusty engine block. The paint held up for as long as I kept the car. Search it on-line and it will explain the chemical reaction. Not all hardwares carry it, but some do.

itiswhatitis1

So if you use it on cast iron sewer line. It will be there as long as you kept the home? Let the other person deal with it.
If there is rust on the cast iron it coming from the inside out. The sewer gas rust the cast out and there nothing you can do than cut it out and replace it. If you get a smell or it start leaking.

nealtw

http://www.hindawi.com/journals/ijc/2011/506501/