What is the minimum concrete thickness when you pour concrete over a newly installed drain pipe?

[wwhitney]

Typical proper build up under an enclosed slab without utilities:

Undisturbed native soil
Coarse gravel layer--no fines--capillary break, flattening
Insulation if required
Vapor barrier, e.g. 6 mil plastic sheeting
Concrete

The practice of putting a layer on top of the vapor barrier is very bad and to be avoided.

Now with DWV in the mix, it should go in one of the first two layers. And you don't want rocks or gravel pressing on the pipe, when things settle or get compacted, a sharp corner could damage or penetrate the pipe. [You also don't want concrete to squeeze the pipe as it shrinks, so you wrap the region of pipe passing through the concrete with a layer of compressible foam.] Plus you don't want to leave voids under the pipe where the pipe ends up unsupported.

So if your native soil has rocks, or won't get well compacted under the pipe, then you use some sand to fill in and cover the pipe. Maybe just 1-2" over the pipe. When your pipe is in the gravel layer, you've got competing interests, as the sand would defeat the capillary break, but protecting the pipe wins out, so you use the sand. The sand also provides a clue to anyone excavating in the future that something is buried there.

Cheers, Wayne

 

[Mini Me]

Thank you for the above, they seem to be in line with these videos
Question: I have some foam left from when I installed my patio door. Is that foam good enough for this application?

 

[Sponsor]

 

[wwhitney]

I would not use spray foam. If the goal is just to avoid pipe crushing, not to create a void for future fittings that the concrete would interfere with, you just want a consistent thin gap. "Sill sealer" is a 3.5" wide or 5.5" wide foam strip used between mudsills and concrete foundations as an air seal. A couple wraps of it would be good.

Cheers, Wayne

 

[Mini Me]

oh OK that is what you meant ? That makes more sense considering the humidity that will be there
I already have a 1/4" of water at the bottom of the hole I dug out for the p-trap.
The hole was OK for a week or two but like three days ago it rained a lot over night here in Toronto and I could see that the dirt got wet
I guess it collected there because of the humidity gradient and because there was excess of humidity in the soil
Would that have been filled with dirt and level I would see no water there ... OK tomorrow I will get some soil to compact around the ptrap in that hole and then add gravel foam and cement. I tested the this afternoon and I have no leaks and the water flows flawlessly from the sing to the drain (no sounds showing that the dry vent we discussed is not working)
thanks a lot for all your advice !!