Plumbing – Fix lead joint between cast iron and galvanized steel plumbing pipes

drain-waste-ventleadplumbing

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:

Re-melt the lead by heating the cast iron P-trap with a MAPP or acetylene torch
Remove excess lead and pack with epoxy putty
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.

Best Answer

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