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I think I have a good idea about how to go about this, but wanted to throw it out here to make sure I don't wander down the wrong path. I recently installed a new floor drain. I broke up the concrete in a circle around the old drain, maybe 14-18 inches in diameter. Under 2-3 inches of concrete was gravel and a few more inches down was the clay dirt under the house. Below is a picture generally representing this. There was a 4" PVC pipe running up from the ground where the old drain was attached. I cut off the old drain and solvent welded the new drain (also PVC) onto the end of the pipe. Now I want to fill the hole back in and finish the concrete level with the new drain.

I have a pile of gravel, broken up concrete chunks and dirt which I excavated from the hole to access the pipe. I could put some of this material back in, maybe fill in around it with sand, building up layers of that until I'm about where the concrete begins in the surrounding slab, and then fill that area in with concrete. Does this sound about right? Am I way off?

Also, I welcome any suggestions on what kind of concrete to use (or what to specifically avoid). Once it's dry, I'll be grinding the surface of it (and the entire floor) in order to lay down a sealer or epoxy or something. It am floor drain of picturing.

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If the PVC drain indicates the age of the plumbing and the house, or at least when the slab was installed, there should be a layer of poly acting as a moisture barrier in between the concrete and gravel. Aside from that, all you need is to add the original gravel back into the hole and repair the vapor barrier and finish off the fill with a bag or two of concrete from any local building supply, big box or otherwise. A detail that would be good to do is be sure the hole cut inti the concrete floor is not all undercut. As in, the concrete should not be broken out so the hole is larger the bottom edge of concrete than the concrete at the floor level. A little undercutting is ok, but the concrete you add needs to lock in so it will not settle down away from the original concrete.

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    Lots and lots of compacting of the layer under the concrete is advisable, as is wetting it and compacting again. – Ecnerwal Apr 24 '16 at 15:31
  • Interesting. I had read some suggestions that I SHOULD undercut but your suggestion makes more sense to me. I'm not sure what the PVC indicates other than I think the slab is original to the house (1959) but all the places that PVC comes out of it, there is obvious concrete patching, and I found a disconnected piece of iron pipe in the ground somewhere. In short, I think all the PVC is newer than the slab. Even the concrete I broke to get the drain out was patching work, not original. There does not appear to be a vapor barrier of any kind (this would be visibly obvious, right?). – bubbleking Apr 24 '16 at 16:38
  • I should also add that the basement has a musty smell that matches the smell of the clay in the hole I dug, so I'm pretty sure the source of that is the vapor that permeates the slab and so there must not be a vapor barrier. I did the ASTM D-4263 plastic sheet test to ensure it wasn't heavy loads of vapor (no condensation formed). My plan is to grind the concrete floor of the entire basement and lay down a sealant of some kind to create a vapor/smell barrier. With this in mind, is the poly necessary? Have I misunderstood something? – bubbleking Apr 24 '16 at 16:43
  • If the sealant is for vapor/moisture proofing, since that is type of sealant you propose to do, that will replace the plastic vapor barrier. Try to do a little research on the product you choose to be sure it has a track record or meets the standard for vapor/moisture barrier, and not just to seal it from getting stained from grease/ oil and the like. – Jack Apr 24 '16 at 21:22
  • Thanks for the tip. I've been trying to research for a few months. It's a confusing topic with a lot of products available. I may ask another question soon about this specifically. – bubbleking Apr 25 '16 at 4:07

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