Hi all... I'm starting my project in a couple weeks and I'm trying to make sure I have all my bases covered.

I will be breaking up some concrete floor and running new drainage beneath it. There are some things I wanted to be sure of:

1) When I run the pipes, it should be sloped so that every foot or so it runs down 1/4" to the ejection pit. Is this correct?

2) I will be putting back the fill I removed then pouring concrete over top. What is the best concrete ix to use? A sand mix or just anything?

3) When I pour, is it ok that I cement right up to all the drains/vents coming out of the floor except for the toilet which I must have some sort of foam to help when I install the flange? What would be recommended here?

4) I sit on an area with springs in the ground and have an average water table. When I pour the concrete to fill the trenches how can I do this to be sure I will not see any leaking of water through the seam (where the new pad meets the old)? Should I maybe pour the new concrete a little lower than the existing pad and "flare" it out so it catches it? My concern is I will either have water leak in or the ground could shift and cause the concrete to lift slightly messing with a rather level floor.

Any help with these questions would be great!

Thanks.

Yes, your pipes should be sloped at 1/4" per foot. Be sure that they are well supported such that the concrete does not cause bends in the pipe.
You should use a concrete mix not a sand mix. If you are using bagged concrete mix, get the high strength. I suggest that you purchase an bag of portland cement. Not a mix, just pure portland cement. The bagged stuff is a little light on the cement part. Throw in a shovel full of cement in each bag of concrete mix as you mix it up. Concrete does not really adhere to other other things. Well, not like glue anyway. I don't think you will have any lifting but you could have water seeping up in the joint. I would mix up some portland cement, just cement, and parge, or coat the sides old concrete with it just ahead of the pour. Pour that area while the parging is still wet. This should give the best waterseal you can get in the joint.

HI Guys!

OK...

1) Correct. 1/4"/ft

2) Concrete mix

3) Correct. Up to the pipes except around toilet pipe.. like you said

4) Do what Harold has suggested... never a bad idea to prewet concrete edges and spread portland cement onto edges before pouring concrete. Adding portland cement to concrete mix can't hurt either!

I usually back cut my trench cuts so that I kind of KEY the new concrete in and under the old floor edges, and I prewet the edges and the ground real good Then feather in so no joint can be seen... use wood float to work concrete first... then when nearly finished, sprinkle a little dry portland cement at edges and finish off with a metal trowel.. the metal will pull moisture to the top and seal edges nicely!

Hope that helps... Mark

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