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jlawrence42 07-11-2007 01:04 PM

Shower and its sub-floor?
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I am planning to build a shower in my downstairs bathroom (see first attached picture). The floor of the bathroom is built on a slab foundation. When I pulled out the old shower, it exposed the plumbing beneath (see second attached picture). As I hope you can see, there is a hole in the slab with a PVC trap that runs into a cast iron pipe. The cast iron then disappears into the slab towards the main waste pipe.

My first question is - what should I do with the hole in the slab? I assume that I want to make a solid, flat sub-floor since the books I have all show a base layer of plywood beneath the shower. A friend suggested that I should pour sand over the plumbing and then fill the rest with concrete. Any thoughts?

agedpaver 07-12-2007 03:47 PM

Hello jl42. I'm not a plumber by any means but I am gathering info on adding plumbing in a basement preferably under my slab. I don't think sand is the way to go here, I have read in another article in this forum that you should use (I believe it was referred to) a "sleave". Sounded to me like a barrier to keep your pipes from being pulled apart by the concrete as it cures. I'm pretty sure you would want to fill that hole with concrete, otherwise you may run intomoisture problems down the road especially since it is a bathroom. Let me know what you find out as you go, I'll be using a concrete saw to get into my plumbing here when it gets underway.

jlawrence42 07-16-2007 10:41 AM

a sleave?
Thanks for the reply. Any idea what constitutes this "sleave"? I looked around the forum and couldn't find the reference. Am I somehow wrapping the pipes in plastic? I'm not exactly sure how I would go about this. Anyone else know?

buick8 07-17-2007 09:04 PM

Hi, it is common for these openings to be left in concrete slabs under tubs and showers for the plumbing drains. It won't hurt anything as long as no support is needed for whatever fixture is over it: tub, shower, etc. Once though little digging animals moles or whatever piled a lot of dirt under my bath tub and I had to remove a wall panel to clean it out. Otherwise it makes it easier for the plumber to align the drain when installing the fixture, as it is not easy (even possible?) to locate the drain pipe perfectly in the concrete slab so it will be in exactly the right place it needs to be. Hope this helps you.

Daryl in Nanoose 07-18-2007 07:04 AM

What kind of shower are you putting in, All tile including base, acrylic, ??

jlawrence42 07-18-2007 11:42 AM

Is pouring concrete a good idea?
Thanks for the replies. I am planning on building my own shower with a plywood subfloor over the concrete slab, then putting down tar paper, metal lath, mortar and the appropriate membranes as recommended in my Black & Decker book. I would then tile the base and the walls (over cementboard).

My feeling is that it seems better to me to protect the underside plumbing (p-trap and drain as shown in pictures) with concrete. I found the previously recommended "drain sleeve" (item #84667) at my local Lowe's.

Are there other opinions as to whether or not I should pour concrete? Can I just put a thicker plywood base over that gaping hole and leave it open underneath as I build the shower above? That just doesn't seem right since I won't be able to access the plumbing down there anyway once the shower is built.


agedpaver 07-23-2007 08:26 AM

I'd be uneasy about using plywood under a shower stall just because of the moisture risk. Seems to me that using plywood would be running the long term risk of rotting out and to repair it in the future would be a pain. Going with the concrete will save the worry and difficult repair since it would mean tearing out the shower and basically re-doing it all over again.

Square Eye 07-24-2007 06:47 PM

You could form up a slab as if you were making a mold
and make a base out of concrete that could be layed over the plumbing.
Much like an A/C pad for a compressor unit.

This would eliminate the swelling and rotting problems associated with plywood. AND, it would still be removeable the same as the plywood.

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