jlawrence42

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?

Jimbob

You friend is right, it's the easiest and cheapest way.

JB

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travelover

I'd agree. If you pour concrete in with no sand, it will be a mess to try to repair, should that ever be necessary. It is not a big job to mix up this much concrete from bagged mix.

glennjanie

Hello JLawerence:
I agree the pipe needs to be resting in and covered with sand, #51 limestone or pea-gravel. This not only protects the pipe from the corrosive effects of the concrete but also keeps the pipe from trying to float up in the concrete. Be careful not to let the water and slurry of the concrete run into the drain; it will plug it up and there is only one way to get it out. Use a plumber's test plug in the drain while the concrete work is going on.
I wish you the highest success with your project.
Glenn