Plumbing 101 – Cast Iron Soil Pipe

Cast Iron Soil Pipe

We are fully aware that quite a number of people around the country will wonder what the heck we are talking about but we thought it was time to talk about cast iron pipe and cast iron fittings. Cast iron pipe and fittings are used in many areas around the country but it’s a fine material and if nothing else this may be a history lesson some day.

Two Kinds of Cast Iron Soil Pipe and Fittings to Choose From

Just to clarify there are two different kinds of cast iron pipe and fittings, hub (bell) and spigot and no-hub soil pipe. No hub soil pipe is much more common than hub and spigot soil pipe. Hub and spigot soil pipe joints are either caulked joints or made with neoprene rubber that are compressed as the pipe enters the hub sealing the joint. No-Hub soil pipe is joined using stainless steel no-hub couplings and gaskets.

Caulked Soil Pipe Joint

When we describe how these joints are made there are some that will think we are talking about pipe used in the early 1900s however just so you know this type of joining method is still used extensively in Chicago even today.

A caulked joint is made with molten lead (We didn’t invent the joining method. It’s nuts) and oakum caulked with caulking irons to make the joint water tight. (Please take a look at the tools listed below.) Lead is available in 5lb ingot and 25lb bars. (Please see a picture of the different types of Oakum and a strand of lead.)

There are two types of oakum used to make plumbing joints.

Brown Oakum

Is hemp fibers that have been soaked in petroleum based pitch to make it water resistant and to protect it from waste water.

Brown Oakum

White Oakum

Some definitions say it is untarred Is hemp fibers but that is only partially true. It is untarred but the fibers are treated with bentonite. Which is a type of drilling mud that swells considerably when exposed to water. It comes slightly damp or moist and when it completely dries out it’s pretty useless. So when the white oakum is exposed to water is expands inside the joint making it water tight. White oakum is the preferred oakum used for hub and spigot cast iron.

White Oakum

The lead is heated on a plumber’s lead furnace (See picture of plumber’s pot and furnace) and poured into the joint with a ladle. Lead should be heated until it is hot enough so that it does not stick to the ladle, but it should never be overheated. Over heating lead will burn it into slag. You will know that the lead is hot enough when the lead no longer sticks to the ladle.

****HOT TIP (Pardon our feeble attempt at humor but it is hot) Be very careful when adding new lead into a pot with molten lead. Lead that has any amount of moisture or that is frozen WILL explode when added to a molten lead pot. Preheat the lead and or cold ladle to evaporate any latent moisture.

Here are the steps to cut and assemble hub and spigot pipe and fittings with yarned and poured joints.

  • Cut the soil to the required length with one of the cutters featured in the pictures below.
  • After the pipe is cut, wipe the hub (bell) and spigot end of the pipe dry and clean it of all foreign particles. Quite often cast iron soil pipe is left outside for storage so the pipe and be damp or frozen in the winter. If there is moisture in the hub molten lead can cause the pipe to split when poured into the joint. In addition any trapped water cause be instantly turned to steam causing a small explosion.
  • Assemble the pipe making sure the pipe and/or fitting is aligned properly. The spigot end of the pipe must go all the way to the bottom of the hub so that the oakum doesn’t push past the the spigot into the pipe.
  • Yarn and pack the oakum into the hub 1” from the top. If you’re using brown oakum you shouldn’t leave any loose fibers protrude into the lead. To remove the stray fibers you can heat the packing iron in the lead pot and burn them away.
  • Pour the molten lead into the vertical soil pipe joint. You must fill the joint with one pour. If you don’t fill it to the top and you try to fill the rest of the joint with another pour the second pour won’t stick to the first and will probably come out while tapping it up.

How Much Lead and Oakum Do I Use?

12oz of virgin lead per inch of diameter of pipe, so 4” diameter soil pipe would require 4lbs of lead. As far as oakum is concerned you use 2”oz for every inch of diameter so for 4” diameter pipe you would use 8oz of oakum.

If you are afraid of moisture in a hub being poured add a couple drops of oil to the oakum. Just a few drops will displace the moisture and allow for a safe pour.

  • On a horizontal soil pipe joints a running rope is used. (A running rope used to be made of asbestos. Asbestos is ridiculously durable but as we all know now is also extremely dangerous if it becomes air born. Now running ropes are made of nylon strands. They look the same but they certainly don’t perform the same. If the nylon becomes too hot it melts and pulls. Most plumbers who have worked with asbestos running ropes wish they had them back.) The running rope is pulled around the pipe and clamped tightly at the top, which forms the “gate” where you pour the molten lead. The rope should be tapped lightly against the hub with the caulking hammer to make sure it fits snugly against the hub so the molten lead will not run out between the hub and the running rope. The lead is then poured into the gate, filling the joint to the top.
  • The running rope is removed after the lead solidifies and the neck of access lead is cut off with a hammer and chisel.
  • After the lead cools in both vertical and horizontal joints the lead is pounded down into the joint with the inside caulking iron around the circumference of the pipe to set the joint. Then the outside caulking iron is used with the caulking hammer around the entire circumference of the joint to finish setting  the lead.

***HOT TIP*** I know there will be old school master plumbers commenting on how you need the right tool for the right job but both the inside and outside of the joint can be pounded down with a packing iron. Most plumbers these day just carry a yarning iron and a packing iron. It does a fine job.

Using Compression Gaskets For a Soil Pipe Joint

In most areas where hub and spigot cast iron is still used compression gaskets are used below ground only. This is a labor issue, some may say that yarned and poured joints are more rigid when hanging above ground but you could beef up the hangers and achieve the same results. Onward….compression gaskets are made from neoprene rubber and made in service weight and in extra heavy (extra heavy cast iron is even more archaic than traditional service weight hub and spigot.soil pipe.) The two types of gaskets are not interchangeable.

Here is how you make a compression soil pipe joint.

  • Clean the hub and spigot so that the are relatively clean of visible dirt and debris.
  • If you are using cut pipe the sharp edge needs to be removed because the edge may catch against the gasket and jam. The edge will not damaged the gasket but it can make it real difficult to join the pipe. You can take the edge off by hitting it with a ball peen hammer or a rasping file.
  • Next you insert the gasket into the hub. Easy right? Not always, here are two ways to get the gasket into the hub.
  • Fold the gasket in half insert the gasket into the hub marking sure the gasket ring will fit into the groove of the pipe and let the gasket unfold itself into the hub.
  • The next method is called the “Bump Gasket Method”. You bump the gasket with the heel of your hand or with something flat like a board until it is fully inserted into the hub.

Preparing the Soil Gasket

Now you’re ready to prepare the gasket and piping for assembly. Using a 2” paint brush apply a thin layer of lubricant around the entire inside circumference of the gasket. Apply lubricant to the end of the pipe being inserted into the gasket.

You can drive the end of the pipe home in one of three ways.

  • If you are doing underground piping you can use a heavy pry bar. You place the pry bar in back of the pipe being installed and push forward until the pipe is inserted fully into the hub.
  • If you are assembling fittings you can use a lead maul to pound the fittings into place. Using lead allows you to give the fittings a pretty good whack without damaging the pipe or fittings.
  • You can use a tool called a “Soil Pipe Puller”. There are a few different styles but they all operate by the same principle. A stirrup goes in back of the hub that the pipe is being inserted into and a chain or jaws are clamped around the pipe. The stirup has a long lever handle on a hinge. The whole contraption is like one big fulcrum. the lever is pull away from the hub pulling the pipe or fitting home.

Assembling a No-Hub Joint

  • Remove the stainless steel jacket from the neoprene gasket. Slide the stainless steel ` sleeve on one side of the pipe being assembled.
  • Apply No-Hub adhesive pipe lube to the ends of the pipe being joined and to the inside of the neoprene gasket. We know that adhesive lube is a bit contradictory but it lubricate upon assembly and when it sets it is rubber adhesive to ensure a good seal.
  • Insert one end of the pipe being installed into the gasket until it hits the separator inside the gasket. Repeat the process for the other piece of pipe. Then slide the stainless steel sleeve over the gasket.
  • Tighten the screw clamps with a torque wrench or other tool for example a 5/16” nut driver, ¼” ratchet with a 5/16” socket or an electric nut driver.

Thanks again for reading from all of us at


  1. We are manufacturing a product DRIPSEAL-PJS-43 (Pipe Joint Sealant) which is used for sealing cast iron pipe joints as substitute of molten lead. It has edge over molten lead in many ways such as cold application, high bonding strength, low labour cost, low transportation, non-toxic and above all, it is highly economical as it cost 70% to 80% economical than molten lead. We would be glad to send more technical details on hearing from anyone.

    1. Thanks for sharing. I just sent an email to you regarding your product. I have never heard of it before but boy am I interested.

      Sean Kavanaugh

    1. An alternative to cast iron? Go with PVC if it’s per code in your municipality. Schedule 40 PVC is super durable, easy to work with and almost corrosion proof.

      Sean K

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