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How were cast iron pipes joined?

Published in Cast Iron Pipe Joining 2 mins read

Cast iron pipes, particularly drainpipes, were primarily joined using bell-shaped hub-and-spigot joints, which were sealed effectively with molten lead and a rope-like material called oakum.

Understanding the Bell-and-Spigot Joint

The method of joining cast iron pipes was crucial for creating durable and watertight plumbing systems. The predominant technique involved the "hub-and-spigot" joint, a robust and time-tested connection.

Here's how it worked:

  • Spigot End: One end of a pipe (the spigot) was plain and designed to fit into the flared, bell-shaped end of another pipe.
  • Bell (Hub) End: The other end of a pipe (the bell or hub) was wider, with a socket to receive the spigot end of the next pipe.

Once the spigot was inserted into the bell, the space between the two pipes was carefully sealed to prevent leaks.

Sealing Process: Oakum and Molten Lead

The sealing process involved two key materials:

  1. Oakum: This was a rope-like material, often made from hemp or jute fibers, that had been treated with tar or a similar sealant.

    • Purpose: A specific length of oakum was first packed into the joint, around the spigot and inside the bell, using a caulking iron. This created a foundational, somewhat flexible seal and prevented the subsequent molten lead from flowing into the pipe itself.
    • Application: The oakum was driven in firmly, ensuring it created a tight seal against both pipe surfaces.
  2. Molten Lead: After the oakum was in place, molten lead was poured into the remaining space in the bell.

    • Purpose: The hot lead filled the void, solidifying as it cooled to create a very strong, rigid, and leak-proof seal around the oakum and against the iron surfaces.
    • Application: Once cooled, the lead was further compressed and "caulked" with specialized tools to ensure maximum tightness and adhesion, preventing any movement or leaks.

This two-step process created a durable and long-lasting connection suitable for drainage systems, capable of withstanding the pressures and movements of typical plumbing applications for many decades.