Plumbing question?

[Bill Morgan]

Not sure if this is appropriate forum. But, I need to move a shower drain line in a concrete slab. I have read that the p trap should be left in a dap out. This dap out appears to be a boxed opening left in the concrete and then houses trap plumbing. I'm unclear as to whether this void would then be filled with concrete to provide a solid surface and seal the slab back up? It seams this would be the case as it would be a moisture barrier as well as for gases(ie radon). Anyone have experience in this?
Thanks
Bill

[Mike Cutler]

Bill

I can't answer your question, but I might point you to two websites that will.

First is Terry Love's Plumbing Forum.
Second is John Bridge's Tiling Forum.

Both sites have a lot of threads about P-traps in a concrete floor, and shower restoration/renovation/replacement projects.

[David G Baker]

I have a basement and the area underneath my bathroom is sand and I am going to leave it that way because if I ever have a leak the water will drain down into the sand rather than into the rest of my basement. I would not fill the area with concrete because at some point every plumbing fixture in a home is going to require some maintenance, this includes "P" traps. If you are really concerned about Radon do the Radon test.

[Troy Donson]

Bill, I'm not a licensed plumber but was a plumber's laborer for 3 years...

You need to cut out and leave a hole around the p-trap at least 4-6 inches in all directions and then after you do your rough in, fill the hole with gravel.

The reason is is that you want the pipes to be able to move and not break when the concrete stays in one place and the ground settles in another direction. Some swear by using concrete foam wrap to cushion the pipes and pour concrete over them, but...

I helped rehab 408 naval housing units at Camp Pendleton which included ALL NEW p-traps at every drain. I personally cut out over 900 old p-traps and even with open areas to move in, the old p-traps got severely stressed from earth movement. The federal inspector actually would measure how much the new ones were "in the clear" before we dropped tubs and shower pans... Plus it gave us some "wiggle room" when dropping the tub/pan. Easier to recut and reinstall some elbows and not have to jackhammer because "Well, it was lined up yesterday when we poured..." That's why it's called "rough in".

I was never worried about radon issues due to the fact that tubs and pans were "caulked and sealed" to the vapor barrier/floor and we had inspectors from our shop, the military and the fed all running around with various black boxes measuring every thing imaginable...


Hope this helps and sorry about being long winded...

Troy