Painting cast iron pipe - odd covering

Chickereeeee

I am planning to paint an old cast iron vent pipe, which I THINK is original (1926 house) but am confused about the current treatment, and how to paint. It seems to have some sort of grey covering, almost like a wrap, which was then painted black. Where the covering has spit at the bottom, the pipe underneath shows through as perfect black, like new.  Further up, the split shows the pipe has heavily corroded. In other places, the black piant is pealing off, and shows the grey covering beneath. Please see pictures.

Has anybody any ideas?

Section62

Chickereeeee said:

I am planning to paint an old cast iron vent pipe, which I THINK is original (1926 house) but am confused about the current treatment, and how to paint. It seems to have some sort of grey covering, almost like a wrap, which was then painted black. Where the covering has spit at the bottom, the pipe underneath shows through as perfect black, like new.  Further up, the split shows the pipe has heavily corroded. In other places, the black piant is pealing off, and shows the grey covering beneath. Please see pictures.

Has anybody any ideas?

At a guess an earlier layer of black paint has been given a thick coat of grey undercoat, then a layer of black gloss.

In some places the black is debonding from the undercoat and peeling, in other places the undercoat is debonding from the layer below.  It could be poor paint, or could be poor workpersonship.

Test the pipe with a magnet to confirm CI (and rule out asbestos cement) then do your best to remove all areas of flaking paint.  If you want to get a really good finish then consider going back to bare metal using paint stripper (safely).  Beware that there may be lead-containing paint involved.

In some cases CI pipes were coated with one of various combinations of tar-like materials with other substances (including asbestos) so if the underlying material appears to be oily then proceed very carefully.

Don't use heat or power tools to remove the paint.

Chickereeeee

Thanks, yes I guess that is the most likely situation. It just looks weird though - immaculate underneath the grey in some places and awful in others (the rust indicating it is not asbestos cement, except possibky to seal joints?). Maybe a piece was replaced more recently and the whole lot undercoated with something. 

Fully stripping the whole pipe would be a very big job. The pipe is now unused, as far as I can see (nothing now connects to it above ground) but it is not simple to remove as it goes though the soffit and roof. I am thinking about a quick rub down, anti-rust and a couple of coats of Zinsser Allcoat Outdoor. Not immaculate, but hopefully better, lasting a few years until I can decide on removal or not. 

Section62

Chickereeeee said:

Thanks, yes I guess that is the most likely situation. It just looks weird though - immaculate underneath the grey in some places and awful in others (the rust indicating it is not asbestos cement, except possibky to seal joints?). Maybe a piece was replaced more recently and the whole lot undercoated with something.

I think it is likely to be CI, but would always allow for the possibilty the rust marks are from iron/steel brackets or other items which have been attached to the pipe in the past.  These could leave rust stains that make it look like the pipe itself is CI.  The magnet test is almost foolproof.

Chickereeeee said:

Fully stripping the whole pipe would be a very big job. The pipe is now unused, as far as I can see (nothing now connects to it above ground) but it is not simple to remove as it goes though the soffit and roof. I am thinking about a quick rub down, anti-rust and a couple of coats of Zinsser Allcoat Outdoor. Not immaculate, but hopefully better, lasting a few years until I can decide on removal or not. 

Vent pipes don't need to have anything visible connected to them to perform their function of providing ventilation.  In the past accepted practice has included separating the ventilation and drainage functions into separate pipes (as well as separating 'grey' water from sinks and baths from 'foul' water from toilets and urinals) - the use of combined stacks with everything in one pipe is a relatively recent evolution.

Compliance with building regs (and sometimes local byelaws) typically requires ventilation - so best not to remove the pipe before checking the sitution that applies in your circumstances.