Oakum is made from twisted natural fibers—traditionally hemp or jute—that are impregnated with tar to create a waterproof packing material used for sealing joints in plumbing, marine, and construction work.
Is oakum a hemp?
Oakum isn't exclusively hemp—it can be made from either hemp or jute fibers, both of which are natural plant-based materials.
Back in the day, oakum was literally old ropes unraveled and soaked in tar to make a waterproof sealant. While hemp was the classic choice, jute became way more popular later because it's cheaper. Britannica puts it bluntly: the real star here is the tar, not where the fibers come from.
Where is oakum from?
Oakum fibers come from natural plants like hemp or jute, often grown in places such as India, Bangladesh, or South America, where jute farming is big business.
Those fibers get spun into rope first, then drenched in pine tar (also known as Stockholm tar) to make them water-resistant. Sure, the raw fibers might travel halfway around the world, but oakum itself gets manufactured everywhere—from small workshops to massive industrial plants—for plumbing, marine, and construction jobs.
Does oakum contain asbestos?
Nope, oakum doesn't contain asbestos—it's just plant fibers (hemp or jute) stuck together with tar.
People sometimes mix it up because older insulation or fireproofing materials did contain asbestos, but oakum never did. OSHA gives it a clean bill of health: no asbestos, no special handling needed.
What type of joint uses lead and oakum?
A bell-and-spigot joint uses lead and oakum to make a watertight seal in cast iron or clay pipes.
Here's how it works: one pipe end is tapered (the spigot) and slides into a wider socket (the bell). You stuff oakum into the gap, then pour molten lead over it to lock everything in place. CISPI (Cast Iron Soil Pipe Institute) calls this the gold standard for sanitary sewer systems for over 100 years.
What do plumbers use hemp for?
Plumbers use hemp fiber as thread sealant for metal pipe connections, often called “pipe dope” when mixed with oil or paste.
The hemp swells when it gets wet, which helps stop leaks between threaded joints. It's usually used with pipe joint compound to create a solid seal in water and gas lines. EPA still lists it as an acceptable sealing method in some cases.
Is oakum still used?
Yes, oakum is still used in traditional cast iron pipe joints—especially in older plumbing systems and heritage restorations where modern sealants just won't cut it.
Sure, synthetic sealants have taken over new construction, but oakum remains the top choice for fixing historic buildings or sewer systems that still use bell-and-spigot joints. National Park Service even recommends it for preserving original infrastructure.
What is the cost of oakum?
As of 2026, oakum usually costs between $12 and $35 per pound, depending on whether it's hemp or jute and how well it's treated with tar.
Don't expect to find it in your local hardware store—this stuff is mostly for restoration work these days. A 5-pound coil for small jobs typically runs about $50–$90. Check out suppliers like Global Industrial or specialty plumbing shops for current stock.
What is an oakum picker?
An “oakum picker” was a prisoner or laborer who manually unraveled old ropes into fibrous strands to produce oakum in old-school penal or workhouse settings.
This was brutal, mind-numbing work in Victorian prisons. Charles Dickens didn't hold back in Our Mutual Friend, calling it “torture by twine.” Today, the term lives on as a dark footnote in labor history.
What does the term smoke and oakum mean?
The phrase “it runs like smoke and oakum” means spreading fast—like fire or gossip getting out of control.
This saying dates back to early 1800s England, comparing quick-spreading news to smoke curling upward or oakum fibers unraveling. Phrases.org.uk traces it to fire-prone cities where alarms spread in seconds.
Can I connect PVC to cast iron?
Yes, you can connect PVC to cast iron using a rubber transition coupling with stainless steel clamps, but only if the cast iron is in decent shape.
Start by cutting the cast iron cleanly with a snap cutter or reciprocating saw. Clean both ends, then apply PVC primer and cement to the PVC side before securing the coupling over both materials. IAPMO approves these couplings for drainage systems. If the cast iron is rusted or buried, replacing it might be safer than trying to patch it.
What is used to join cast iron pipes?
Cast iron pipes are joined using lead, cement mortar, rubber gaskets, or mechanical couplings like “No-Hub” bands, depending on the system.
Old-school hub-and-spigot joints rely on lead and oakum or cement mortar. Modern hubless systems use rubber gaskets squeezed by stainless steel bands. CISPI standard 310 covers hubless installations.
How do you fix a leaking cast iron pipe?
To fix a leaking cast iron pipe, shut off the water, clean the area, then apply a two-part epoxy or cast iron repair paste over the leak.
- Turn off the water and drain the system completely.
- Use a wire brush to sand the leaking spot until it's rust- and debris-free.
- Spread the epoxy or paste evenly with a putty knife, making sure to cover the leak completely.
- Let it cure for a full 24 hours before turning the water back on.
For bigger breaks, you might need a stainless steel repair clamp. Family Handyman warns this is only a temporary fix—eventually, you'll want to replace the pipe for good.
What are the two types of cast iron pipe?
Cast iron pipes come in two main types: hub-and-spigot and hubless (also called no-hub), each built for different installation styles.
Hub-and-spigot pipes have a bell-shaped end that fits the spigot of the next pipe. Hubless pipes skip the socket and use external couplings instead. ASTM A74 and CISPI standards cover both types.
What are the three ways to join cast iron pipe?
Cast iron pipes are typically joined by caulked lead and oakum, compression gaskets, or hubless couplings.
Caulked joints involve stuffing oakum into the socket and pouring molten lead over it. Compression gaskets use rubber seals held tight by a mechanical collar. Hubless couplings wrap around the pipe ends with stainless steel bands. PM Engineer says hubless systems are the go-to for modern retrofits.
How is cast iron plumbing connected?
Cast iron plumbing is most commonly connected using lead and oakum in bell-and-spigot joints, where oakum is packed into the joint and sealed with molten lead.
The oakum expands when wet, forming a tight seal, while the lead locks it all in place. This method has been around since Roman times and still works great for underground sewer lines. Smithsonian archives show examples from 19th-century systems still in use today.
