Well no good deed goes unpunished. Any ideas on how to clean the threads from a cast iron waste stack?
spouse and I tried to help our daughter fix her pedestal sink in her 80 yr old house. The 1 1/2 " galvanized threads for the drain were rusted and broke off. Tried to remove that from the cast iron angle and the pipe crunched down as it was pretty rotten with rust. Then we open the wall in back of the sink and tried to cut the 1 1/2 " galvanized pipe which was after the angle and that pipe was rusted through also and broke off in the cast iron stack leaving pieces in the threads. We called a plumber after trying in vain to get the threads cleaned with a wire brush and picking at the pieces of pipe. Over the phone, the plumber indicated he might have to open the whole wall to replace the main stack if he can't "freshen" the threads. Any ideas on how to avoid that would be appreciated.

Do you have a picture of the remaining broken piece/fitting? Is the stack galvanized or cast iron? If the stack is in ok shape and the only issue is the stuck threads, opening just enough of the wall to replace the fitting should work instead of opening the whole wall.

Don't have a pic at this time. The waste stack is 4" cast iron. The threads in question are the the ones in the 4" stack that accepts the 1 1/2 galvanized pipe. Some of the rusted pieces of the old galvanized pipe are stuck in the threads. The sink was wet vented to the stack via the 1 1/2 galvanized. The run was only about 2 1/2 feet total to through the wall.

you will need an NPT 1-1/2" tap to 'chase the threads'

the 'plumber' you called should have one

you will also need the proper tool to 'drive' the tap

they are large and EXPENSIVE



==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

We faced the same in our 1917 four square that we renovated in NY. We ripped the band aid off so to speak and replaced the cast iron stack with PVC. Not sure what the condition of the house is, or what stage the reno is in, but if the pipe was in that bad shape at that sink it's just as bad everywhere else. Yes, you can pay a plumber (licensed/bonded/insured ONLY) to chase the threads with a 1.5" pipe tap but the money you spend there might be better invested in replacing the whole stack. Yes it's a pain but it's not going to get any better.

Think there is any chance of chasing the threads with a large wrench driving the tap? I found the tap for $34 online. The rest of the stack seems ok, and the run from the tub to the stack was no problem before. The galvanized was replace with PVC with no problems encountered with the stack. Oh to elucidate the previous tub run was performed by a licensed plumber and is the same one we called this time. He can't get to it until a week from Friday.



Edited 2 times.

All right -- I'll bite -

Bernabeu,

Please educate me - What is the proper tool to "Drive" the tap ?

At the risk of embarrassing myself....I've just used an adjustable wrench to drive my large pipe taps. So far no problems.

or



whatever drive tool + 12 point socket works

one can always try a 1" drive ratchet and appropriate 12 point socket to reach threads in a wall

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Use a hacksaw blade or= and slicing into the inside of the galvanized make 2 cuts about 1/2" apart, stopping cutting just as the threads start to show. Then with a small chisel or= knock out the small wedge you cut. Use the chisel on the edge of the remaining to start to fold it in. Prying and twisting with pliers lets you get the rest out, often easily.

Thanks Bernabeu.

Never knew the proper name for that tool.

i have forgotten the 'proper' name

'Armstrong Stock' is the usual 'call'

like channel locks instead of 'adjustable slip joint pliers'



==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



Edited 1 times.

I know the tool as a tap wrench or tap handle. Another consideration if using a tap for this project is that you would probably need a bottoming tap.

nope ....... standard NPT tap will suffice for 'chasing' as there IS clearance behind/beyond the (F)NPT threads


ps. never ever heard of a NPT bottoming tap

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



Edited 1 times.

The 1 1/2" bottoming tap I have may be a tap modified by one of my grandfather's machinist buddies, but I never use it. I make two cuts, chisel out the wedge, fold in the remaining chunk of nipple then pull it. We will have to agree to disagree on all that. It makes no sense to me for a homeowner to buy that tap and a holder (even assuming there is room to spin it) when the job can be done with a hacksaw blade with a rag handle, a beat up old screwdriver, a hammer and pliers. The threads inside the fitting can normally be cleaned up with a wire brush. But, that is me.

me too

absolutely correct method to remove a 'broken' threaded 'stub' from a fitting


i agree, just like i stated to the OP, it is not cost effective for the typical HO to try a 1-1/2 tap


however, 'sometimes', one needs to 'chase' a (F)NPT after removing a 'stub' and wire brushing the threads


THEN


one would be wise to hire an actual plumber


(who may rightfully recommend entire stack replacement)

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Quote

Think there is any chance of chasing the threads with a large wrench driving the tap? I found the tap for $34 online. The rest of the stack seems ok, and the run from the tub to the stack was no problem before. The galvanized was replace with PVC with no problems encountered with the stack. Oh to elucidate the previous tub run was performed by a licensed plumber and is the same one we called this time. He can't get to it until a week from Friday.

YES, you can turn the tap using whatever tool you want PROVIDING you keep the tap 'straight' and you have sufficient OOMPH - remember: you are merely 'chasing' the EXISTING threads from which you have REMOVED the broken 'stub' of the previous pipe


You can NOT, repeat NOT, use the tap to remove an actual 'stub' of a broken pipe from a fitting - you CAN use the tap to 'dress' the fitting AFTER the stub is removed.

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Spouse here. In this particular case there wasn't a stub left sticking out, just the rusted remains of the galvanized pipe in the threads and because of the placement and nearness to a 2X6 stud, no room the use a pick, screwdriver or anything else to get to the pieces. So we did get the tap ($35) and using a 3/4" ratchet, extension, and very large 6 point socket, and heavy oil (all items we already have for working on farm machinery) hubby was able to chase the threads clean. Yea!!! Put in a 6" galvanized stub with plenty of pipe dope and transitioned to PVC with a mission coupling. Tested for leaks and closed up the wall. Saved our daughter several hundred dollars I am positive. I'm sure this fix will last for enough time (at least ten years) that she will eventually sell the house and the next owner will have the headache of replacing the cast iron stack, which I am sure will need to be done at sometime in the future. Thanks to all for your comments and wisdom. We wouldn't have tried it without all the input. This site has been a blessing for us with our projects, this one included. Bless you all.



Edited 1 times.

Quote

..... and using a 3/4" ratchet, extension, and very large 6 point socket, and heavy oil (all items we already have for working on farm machinery) hubby was able to chase the threads clean.

good work


you actually HAD the 'proper' tools (except the tap itself)



not practical for the 'typical' DIYer

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Totally agree. Most people won't have the other stuff also. So hiring the plumber would be the cheapest option.

it was easy showing a farmer how to plumb ..................

now for the miracle:


teach me to farm ............................



==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I guess farmers aren't your everyday DIYer's. As for teaching somebody how to farm, I wish I knew! Our lives hang on the whim of weather.