I took out my bathtub to replace a rotted wall behind it, and the drain pipe fell out. (Yes, I unscrewed the drain fitting before removing the tub.) The joint under the concrete slab, where the drain pipe meets the P-trap, is what came apart.

drain pipe and P-trap http://www.bolis.com/albums/projects2014/20140528_130558_bathroom_plumbing.sized.jpg

The P-trap is below the concrete slab, and not right under the tub drain, so it was extended up to the tub drain with two 45-degree elbows. The P-trap is cast iron, and so are the two 45-degree elbows. The pipe nipples joining them are galvanized steel, US 1-1/2 inch NPT.

The P-trap, however, is not threaded, at least not with 1-1/2 NPT threads. It looks like there could be a smaller, finer thread; it might be tub drain fitting threads. Or it might just be my imagination; it is hard to tell with the rust.

It appears that the steel pipe nipple was set into the P-trap and sealed with lead. The lead made sort of a gasket, sitting in a lip or shoulder of the P-trap. The lead ring was peeled up slightly on the left side. I imagine it may have had a small gap with a the P-trap for a long time. I attempted to peel it off with pliers, as you can see, but it is held quite firmly on the right-hand side.

P-trap http://www.bolis.com/albums/projects2014/20140528_130530_bathroom_plumbing.sized.jpg

P-trap http://www.bolis.com/albums/projects2014/20140528_130409_bathroom_plumbing.sized.jpg

This type of connection is used elsewhere in the house. Here is another one nearby, which I think is for a vent stack. lead pipe joint http://www.bolis.com/albums/projects2014/20140528_130510_bathroom_plumbing.sized.jpg

The house was built in 1966, and I assume this is original construction.

I scraped the joints with a knife, and I'm quite certain they are lead. There is no clearance gap between the galvanized drain pipe and the cast-iron P-trap hub. There is no oakum; this is not a bell-and-spigot leaded oakum joint.

So: what's the best way to repair this pipe joint? I have replaced the bottom pipe nipple on the drain pipe with a new one, but how should I reconnect it to the P-trap?

I'm sure I can clean off the old P-trap and set the drain pipe back in place (after I measure and position it carefully to line back up with the tub). How should I reconnect it? I can imagine several alternatives:

  1. Re-melt the lead by heating the cast iron P-trap with a MAPP or acetylene torch
  2. Remove excess lead and pack with epoxy putty
  3. Dig out the P-trap and replace with a threaded one, perhaps in a better location.

I really don't want to replace the P-trap buried under the slab if I can avoid it. I'm leaning towards trying to remelt the lead, but I don't know what pitfalls to avoid.

Advice? Suggestions? Thanks in advance for any help.

  • IMHO, and I'm a guy that knows how to use a torch, this one might be better to deal with by calling a plumber (first verifying that they are an old-school plumber that can deal with making lead joints, not of the "this rubber boot will do it" school.
    – Ecnerwal
    May 28, 2014 at 21:42
  • A lead and oakum cast iron joint continues to be an acceptable way to make up cast iron joints under most codes, though everyone now makes up clamped no-hub joints. Hard to do if you have an existing hub fitting! Melting the lead in place is not a good idea, you cannot be sure everything is fully molten, the surface will look good but you will have a faulty joint. If you do chose to work with molten lead, wear appropriate protective equipment and only handle it in well ventilated areas.
    – bcworkz
    May 29, 2014 at 0:57

3 Answers 3


Re-leading the joint isn't too hard. You will need a slug of lead, a ladle, yarning iron, packing iron, caulking irons, oakum, and torch. The process goes like this:

  • Safety first! Wear thick leather gloves and avoid eating lead particles.
  • Clean the old lead out
  • Using a yarning iron, pack the oakum around the pipe. Repeat this operation until the hub is packed to about 1” from its top. Pack the oakum with a hammer and packing iron to make a bed for the molten lead.
  • Using the plumber’s ladle, carefully pour the molten lead into the joint, as shown in Figure 30. Dip enough lead to fill the joint in one pouring. Allow a minute or two for the molten lead to harden and change incolor from royal blue to a dull grey. Usually, one pound of lead is melted for each inch of pipe size.
  • Caulk the joint first using the outside caulking iron and then the inside caulk ing iron. The first four blows should be struck 90 degrees apart around the joint to set the pipe. Drive the lead down on the oakum and into contact with the spigot surface on one edge and the inner surface of the hub on the other. Use firm but light hammer blows.

The process isn't really hard at all for vertical pipe, but does require some specialized tools. If you have several of these joints in your house, it might be worth the investment!

Yarning irons:

Yarning Irons

Caulking Irons:

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Inside/Outside Caulking Irons:

enter image description here


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Horzontal Pour:

enter image description here

  • 1
    No, this is not an oakum-sealed bell and spigot joint. There is no clearance between the 1-1/2 inch NPT galvanized pipe and the cast-iron hub in which to fit any oakum. The lip around the shoulder on the hub is only about 1/4 inch deep. This is definitely a different sort of joint. (Hmm, shouldn't you at least credit a cut-and-paste from assiniboine.net/user/staff/grimeaulj/… ?)
    – Grunthos
    May 30, 2014 at 15:13
  • I would have just linked to it but linking is frowned upon and for some reason image uploading via url was broken... in any case, could it be that the old nipple was threaded in there and sealed with the lead cap (didn't have teflon paste back then? idk). You could potentially use a smaller diameter nipple, giving you room to use oakum/lead around the pipe.
    – Ethereal
    May 30, 2014 at 16:14

I bought a Neoprene boot which fit around the pipe and the P-trap. It worked.

I packed the gravel back in around it and it held everything securely.

neoprene coupling

  • Wrap anything in ground in plastic and seal it off. Those metal straps will eventually rust and fall apart if exposed to moisture.
    – DMoore
    May 31, 2014 at 3:52
  • They're stainless steel. What sort of plastic do you recommend, and how would you seal it? I would expect duct tape to last shorter than stainless.
    – Grunthos
    May 31, 2014 at 4:01
  • plastic and zip ties
    – DMoore
    May 31, 2014 at 4:17
  • Bands are stainless, but you need to make sure the worm screw is as well. I've seen many with cad plated steel worm screws. Jun 9, 2014 at 22:35

I would:

  • dig out more until you are at solid pipe.
  • cut pipe out there
  • fit with appropriate coupling (something like this)
  • build up with PVC

Also note that during your refill that the area that the coupling is in needs to be packed tight so it doesn't move. I also wrap the couplings in thick plastic and tape each end up to keep moisture off coupling.

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