Staining on waste line in basement.


  #1  
Old 12-30-14, 08:16 PM
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Staining on waste line in basement.

The soil stack and main waste line in my basement (old cast iron) has some staining near the joints. It looks like a damp oil stain, although obviously not oil. I am assuming it is typical and not a big deal (is that an ok assumption?)

It has been there as long as I can remember, I just never cared until now since I am looking to paint it. I'm guessing paint wont stick to it in those spots.

Does anyone know what the cause is, if it is a big deal, if I can just paint over it, or how to prepare so I can paint?

Thanks so much and happy new year.
 
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Old 12-31-14, 03:56 AM
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You need to clean the stain the best you can [mainly remove any residue] and them use a solvent based primer. The primer should prevent the stain from bleeding thru your finish paint. The stain should only come back if it is an ongoing leak.
 
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Old 12-31-14, 04:46 PM
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Your first impression that it is an oil stain may very well be true. Bell and spigot cast iron is joined by using a material called oakum packed tightly into the belled end. Oakum is tarred jute fibers and since tar is a petroleum product it IS oily. What you are seeing might just be some of the tar/oil that leaked out prior to having the lead seal poured.

Mark is correct in that you need to wash off as much as possible using a petroleum-based cleaner such as mineral spirits and then priming with something like pigmented shellac. After that you should be able to use any paint as a finish coat.

Now IF you determine that it is an on-going leak then it will require "caulking" the lead seal at the leak point. This entails using a blunt punch and carefully hammering the lead tighter in the joint.
 
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Old 01-05-15, 07:53 AM
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Interesting. I assumed it was kind of residue from the waste that has been flowing for so many decades. But the pipes looks well-sealed and in decent condition, so I guess it is oil.
 
 

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