While modern plumbing relies heavily on no-hub bands, push-to-connect fittings, and PVC or PEX, many people don’t realize that for decades, lead-and-oakum joints were the primary method for sealing cast iron drain lines. This blog will explain how these classic joints were prepared, why lead was the material of choice for drainage, and how the entire process—from melting lead blocks to packing oakum—actually works. You’ll also see why this method, though now uncommon, still shows up occasionally in specialized contexts.
Early Days of Lead in Plumbing
Plumbing with lead is ancient. Romans built entire systems of lead pipes (the word “plumbing” is from the Latin “plumbum,” meaning lead). Up until the mid- to late 20th century, cast iron drain lines were sealed using molten lead poured into the joint after being packed with fibrous oakum. This approach was standard for sewer and drain connections, not for potable water supply. By 1986, lead was banned for drinking water lines in the United States under the Safe Drinking Water Act, but lead in drain lines persisted longer because it isn’t directly contacting your drinking water and is considered less hazardous in that application. Despite the advanced age of this technique, it’s still legal for certain sewer or drain uses, and some plumbers still do it for repairs or specialized projects.
Why Lead and Oakum
Lead has a low melting point, around 621 °F (327 °C). This allows plumbers to easily heat small blocks of lead in a lead pot and pour the molten metal around the pipe’s hub. Oakum is a fibrous rope impregnated with oils or tar that, once tightly packed in, expands with moisture and helps form a seal. These materials combine to create a robust joint that is water- and gas-tight.
• Oakum acts like a gasket. When it gets damp, it swells, helping seal gaps.
• Lead, once poured, cools rapidly and forms a dense metal ring. This ring, hammered or “caulked” with irons, compresses the oakum and creates a permanent lock around the pipe.
• Because cast iron piping often handles drainage or vent lines, some minimal exposure to lead is considered less of a risk. Still, lead dust or fumes are unhealthy, so protective gear is essential.
Equipment Needed for a Lead and Oakum Joint
• Blocks of Lead: Usually sold in rectangular bars or smaller pieces. A typical older plumbing truck would carry a pot full of scraps and newly added bars.
• Oakum: This looks like thick, tarred rope. It can be unraveled into strands if the rope is too thick for the space.
• Melting Pot and Burner: A metal pot (the “lead pot”) to hold the blocks while melting, plus a propane or natural gas burner.
• Ladle: A solid metal ladle for scooping molten lead from the pot and pouring it into the joint.
• Caulking Irons (Inside Iron, Outside Iron, and sometimes a Flat/Set Iron): Each iron has a distinct shape to compress the lead toward either the inside diameter of the pipe, the outer hub side, or flatten it all around for a perfect seal.
• Running Rope (or “running joint rope”): A specialized rope clamp that seals off the bottom of the joint so the molten lead can be poured from above. This rope is then removed after the metal cools.
Step-by-Step: Pouring a Horizontal Joint
Many lead-and-oakum demonstrations show a vertical joint because it’s more common in stacks, but horizontal ones require more skill to avoid leaks.
-
Clean and Prepare
The cast iron hub and the pipe end must be free of debris or dirt. If there’s an old lead joint, it might need chiseling or partial removal. Position the pipe so its spigot end fits snugly into the hub. Some plumbers rig small blocks or braces to keep the alignment perfect. -
Pack the Oakum
Oakum comes as thick, tarry rope. You may unravel or split it if it’s too big for your gap. Wrap the oakum around the spigot inside the hub, pressing it tight. Use a caulking iron and hammer to drive the oakum in place. The goal is to fill the annular space except for about one inch at the hub’s outer edge, leaving room for lead.- Keep checking that the pipe remains centered and your oakum is evenly packed.
- A smaller iron helps push oakum into tight corners.
- If you have lumps or strands protruding, trim or tuck them in neatly.
-
Set the Running Rope
A running rope is a rope clamp that seals off the underside of the hub gap. Place it so you have a neat triangular opening at the top for pouring. Press it firmly, making sure it contacts the cast iron all around, preventing molten lead from running out the bottom of the hub. -
Melt the Lead
In your lead pot, place lead bars or scraps. Fire up your burner to heat it until it liquefies. Skim off any impurities or dross on the surface. Overheating can produce lead fumes, so good ventilation and proper gloves, apron, and eye protection are mandatory. -
Pour the Lead
Fill a ladle with molten lead. Carefully pour into the top of the joint. For a horizontal joint, you may do this in one or two pours. The first pour might fill most of the gap, and a second pour tops it off. Watch for overflow or leaks around the running rope. If done right, the lead won’t spill out.- Never splash water on molten lead; it can create dangerous steam explosions.
- Maintain a steady hand. The lead cools fast, so you must work confidently but without panic.
-
Remove the Rope and Trim Excess
Once the lead solidifies (which doesn’t take long), gently remove the running rope. Any extra lead may form a small triangular protrusion on top. You can tap or cut it off with a cold chisel. -
Caulk the Joint
Using the inside iron, push the lead down toward the pipe. Switch to the outside iron, pushing lead toward the hub. Finally, a flat iron packs it uniformly. These steps compress the lead so it’s locked into place, ensuring no water or sewer gas escapes. Skilled plumbers often spin or mark the hot lead, or place initials on it as a signature of pride.
Why No One Does This Much Anymore
Modern plumbing uses no-hub bands, rubber gaskets, or push-to-connect fittings for cast iron. These methods are:
• Faster and safer (no molten lead or lead fumes).
• Easier to train apprentices.
• Code-friendly in most jurisdictions.
Still, some restoration projects or specialized repairs might call for lead-and-oakum if an existing line is leaded or if the job specs require it for historical accuracy. Some older plumbers keep the skill alive for unique situations.
Safe Handling of Lead
Lead’s toxicity is well-documented. When performing a lead pour:
• Wear gloves, a face mask, and safety glasses.
• Avoid inhaling fumes or lead dust.
• Keep your work area well-ventilated.
• Store leftover lead scraps away from living spaces, preferably in closed metal containers.
• Thoroughly wash your hands and clothes after working to prevent contamination.
Is Lead Allowed Today?
The 1986 Safe Drinking Water Act amendments banned lead for pipes or fittings that carry potable water, but cast iron drain lines for sewer use remain an exception. Because this pipe handles wastewater rather than drinking water, the code still permits lead in certain locales. Always verify local plumbing codes or ask your inspector if lead-and-oakum joints are acceptable.
Comparing Old and New Methods
• Lead and Oakum: Extremely durable, high compressive seal, but time-consuming and hazardous.
• No-Hub Coupling: A rubber sleeve and stainless steel band that clamps over the cast iron spigot and hub. Rapid installation, easy to adjust, but not “classic.”
• Hubless Cast Iron: Eliminates the hub entirely. Joints are made with a neoprene gasket and a metal band.
• Rubber Gasket: Often used in modern bell-and-spigot cast iron—simply push the spigot in. No molten lead required.
Lasting Impact
Many older buildings still have functional lead-and-oakum drains that have held tight for decades or even a century. This testament to craftsmanship shows how a well-done lead joint can be as permanent as the building itself. While professionals rarely do these joints for new construction, understanding them helps you appreciate the evolution of plumbing.
Conclusion
Learning “How Plumbing USED to be Done” with lead-and-oakum joints opens a window into a time when the plumber’s skill with a ladle and a set of irons defined the reliability of an entire drainage system. Although it may not be standard practice anymore, this method remains a fascinating piece of plumbing heritage. If you’re ever restoring a historic property or running into an older cast iron system, knowing the basics of lead-and-oakum can be invaluable. Just be sure to prioritize safety, code compliance, and proper disposal or handling of lead at all times.
