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drh 02-01-2008 11:29 AM

Advice needed - Use ABS or PVC for waste pipe under our basemenst slab?
Hello DIY'ers - would like to turn to you for a third-party opinion here.

We're in the process of lowering our basement floor, and has uncovered some old clay piping that was installed 60+ years ago -- as you can imagine, it's cracked and caving in at spots, so we need to replace.

As you can imagine, I've had many plumbers come in and give me their opinion on what materials to use, and as a result, their prices seem to swing wildly.

Basically - I have one plumber telling me we should use ABS 4" all the way, from the cast iron stack to the city connection, while another tells me ABS is way overkill and that PVC is the material of choice. The price difference between ABS and PVC is quite large. We also need to snap off part of the stack and replace it -- should we use ABS? or PVC?

From the research I've done, I'm seeing that PVC is typically what's used for the waste piping, while ABS is used for floor and toilet drains.

The question is, which one is right? Am I really "better off" using ABS (the plumber tells me is a much better product, it's strong and will not "crack" over time - something PVC will.

Dan in Canada

dyier 02-01-2008 11:48 PM

Different areas use one or the other. Check your local Home Depot or Lowe's plumbing department. What ever they stock the most of in DWV fittings and pipe will tip you off on the approved material in your area. Important: where ever the pipe will come in contact with or pass through concrete shoud be wraped with thin foam wrap! Make sure you have fall, 1/4" per ft fall for 3" or less and 1/8" per ft fall for 4"

Hot's on the left, Colds on the right, and crap flows down hill.

Chris Johnson 02-02-2008 12:21 AM

Dan, Ontario accepted PVC below the slab or grade, once you penetrate the concrete floor into living space you had to go to ABS. You have a cast stack? Careful!! it's heavy, PVC cannot handle the weight or pressure of cast (Normally thin wall (Sch. 40) is what is used in Canada for all those US plumbers reading this). So support that cast iron before cutting it loose or you will be sorry. attach your ABS to it below the slab, make the bend (in ABS) then convert to PVC make sure you have the right fittings and the right glue to transition from ABS to PVC (expensive comes in small quantities).

Watch your cast iron pipe for rot from the inside, you'll know it when you cut it, it'll be soft and not snap too well with a cast iron pipe cutter, I ran into a lot of this in Toronto and you could be replacing more pipe than expected.

DYIER - Add to your list...paydays on Fridays and don't stick your fingers in your mouth

drh 02-02-2008 01:16 PM

Chris, many thanks for the advice - I'm also in Toronto so your advice is especially useful. Yes, we still have a cast stack, which I'm told should be "clamped" above each level of the house. Hence even if we cut it in the basement, the above two floors should hold the weight of the stack in place. Either way, we will additionally brace it from below.

The plan is to use ABS from the clipped portion of the cast stack down to (as you said) the elbow to the slope below grade. From there on in, we plan to use PVC, being extra careful to pack in gravel under and around the pipe so that we don't have movement (especially after we pour).

We plan to replace the cast up to (near) the ceiling of the basement, replacing the rest of the cast as we work our way renovating each floor up. The cast is 70+ years old and will likely be in need of replacement anyway.

Thanks again for the advice!

Marlin 02-03-2008 06:27 AM

Never rely on advice from Home Depot. They sell tons of stuff that isn't approved and the guys working there although sometimes seemingly knowledgeable and willing to help, most of the time have little to no idea what they're talking about. Think about it, why would a plumber be working at Home Depot for $13/hr when they can go out and work as a plumber for $30/hr.
The absolute best thing to do is call the local inspector or building department. They will give you accurate and free information.

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