Waste-Pipe Trade-offs

Plastic's light weight means one person can install it alone. But here again, there are tradeoffs. “You always need a two-man crew for cast iron,” says Ballanco. “But using no-hub connectors, two men can install iron in half the time that one man takes to install plastic. So in terms of total man-hours, the two are almost the same. A lot of people don't understand that.”

The no-hub connectors use a flexible synthetic rubber sleeve and metal compression straps. They're reliably leak-proof, but not as rugged as an old-fashioned lead-and-oakum joint. Structurally, no-hub joints are weak points that require support hangers to be located close to each joint. On the other hand, cast iron can span 10 feet between supports, while plastic pipe needs support every 4 feet—but with a lighter-weight hanger. “The cast-iron guys say, ‘We don't need as many hangers,' but then the plastic guys go, ‘Well, our hangers are easier to put in.' And there is truth in both arguments,” observes Ballanco.

Both plastic and cast iron are materials for the ages. “Cast iron, we know, will last for an eternity,” says Ballanco. “There is no denying that. And the plastic guys will tell you, ‘Ours is the stuff that the environmentalists say, when you dig up a dump in a thousand years, will still be there.' So plastic has longevity too.”

But iron's greater strength comes into play when pipes have to be buried. “If you install plastic correctly, you'll have no problem,” says Ballanco, “but it takes more to properly trench plastic than it does cast iron. With cast iron, you can throw basically anything into the trench. With plastic, it has to be a properly bedded trench.” Fill selection is key: “They started out with sand, and then they tried pea gravel. Well, sand didn't work. Pea gravel was terrible, because it moves. Then they found that regular gravel works wonderfully—but it can't have big chunks.”

There's an American Society for Testing and Materials backfill standard for plastic pipe trenches, says Ballanco, but commercial contractors often use gravel. “They don't want to screw around. Home builders typically just say, ‘Okay, keep the big rocks out and start compacting.'”

HANGERS ON: Plastic drainpipe has to be supported at close intervals by approved straps. Iron pipe can span farther between supports, but the heavier iron pipe also requires more substantial support hangers.

Backfilling quality is a particular challenge right next to the foundation. Says Ballanco, “Some plumbing contractors hate the fact that they can't control conditions where the drain exits the foundation. So they use a cast-iron 10-footer at that spot, even if they run everything else with plastic. That's their assurance that the builder can't screw up their installation close to the foundation.”