BOOM! I STOOD transfixed as it dawned on me that no molten lead remained in the pot. Instead, thousands of steaming dots of lead were strewn about over a fairly wide area of our shop.
One of my jobs as an apprentice was to melt lead drainage lines and lead pans removed from old showers in order to pour pigs for reusing this versatile material — an early version of recycling!The ladle had been exposed to rain during a morning service call because it was in the back open bed of a pickup truck. Plunging it deeply into a full pot of molten lead had caused the immediate change in state from liquid water to steam and a violent expansion 1,700 times in volume, which immediately displaced the molten lead.
In that bygone era, we packed cast-iron joints with oakum and poured molten lead over the oakum along the top 1 in. of the bell-and-spigot joint. Oakum, it was explained to me, created a watertight seal by expanding greatly when wet. The lead was merely the stopper that prevented the oakum from escaping the joint, and the piping created the block along the interior. The oakum had no choice but to expand within a confined space, which prevented liquids from escaping.
Paul Strayer, the journeyman I spent most of my apprenticeship with, laid out the array of packing irons I’d need to purchase and carefully taught me the art of making lead joints. He had me “season” my new joint-runner (a braided rope that was used to keep molten lead contained within joints until it solidified) by submerging it in cutting oil for a week in order to prevent molten lead from attaching itself to the runner.
In spite of skinning my knuckles a time or three and occasionally smacking a finger with my hammer instead of the packing iron, I learned the art.
Why did oakum expand and what in the heck was this oily stuff anyway? And why did it smolder so intensely whenever we melted out an old lead joint? The answers came during a summer’s vacation tour of a maritime museum.
Oakum fibers were mixed with tar in that bygone era and packed into joints between wooden-hulled ship planks to make the seams leak-proof. Oakum fibers come from the bark of the jute plant, which grows in wet tropical locations. It’s easy to envision how oakum made the transition from shipbuilding to utilization in the plumbing trade.
Bentonite clay, a substance derived from volcanic deposits, expands greatly when exposed to moisture and is mixed in with the fibers of the oakum used in packing lead joints. Once the pipe is properly aligned within the bell, oakum is stuffed into the opening with a yarning iron. Successive layers are packed tightly until about an inch below the rim. Along the rim, there’s an annular ring, which is designed to “lock in” the poured lead.
The days of maintaining a full pot of molten lead are long gone, but pouring a lead joint can be accomplished by melting a ladle-full with a hand-held torch. If you’re pouring cast-iron-to-cast-iron joints, gently rock the ladle until the lead no longer clings or curdles along the edges and its surface color begins to darken slightly. If you’re making a transition to plastic, a caulk ferrule should be utilized to withstand the temperature abuse instead of simply stuffing a section of piping into the bell.
For cast- iron-to-plastic joints, continue rocking the molten lead gently until it begins to skin over and then quickly pour the contents into the joint.
As the lead cools, it will contract somewhat. Once it’s cool enough to touch without pain, you’ll need to use a caulking iron to expand the lead within the joint. The caulking irons our local inspectors required had crosshatch marks along their surface, which let them know at a glance we had properly caulked our joints.
I learned the hard way that combined lead/plastic joints had to cool completely and be treated much more gently when caulking!
Paul enjoyed challenging my skills. I can clearly remember the day he had me pour an upside-down lead joint in a 4-in. stack where a 2-in. vent was to be connected using an inverted 4-by-2 wye. Where the lead-runner turned upwards, the open gap was carefully dammed with oakum. Keeping the lead runner tightly clamped and firmly against the pipe’s bell created a channel for molten lead to follow. Superheating the lead ensured it would remain molten long enough to run completely around the circumference and rise up within the joint.
I’d like to say my first few attempts were an immediate success, but the truth is it took more than a few tries before Paul would accept the results. The solidified lead trail leading back up into space was chiseled away and the joint packed.
Working with molten lead is dangerous and should be not be attempted without proper training and safety equipment.
Dave Yates owns F.W. Behler, a contracting company in York, Pa. He can be reached by phone at 717/843-4920 or by e-mail at [email protected].
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