Filling a hole in my basement floor

[Lucky Recardito]

I live in a 125-year-old house. The basement is unfinished (and will never be finished, at least not by me), but is heavily used for laundry, storage space, and working out.

Basement floor is poured concrete, but it probably started life as dirt. Not sure when the concrete would have been poured, but it's certainly not new. Near the front wall there is a hole in the floor. About 1 foot wide, 2 feet long, 1 foot deep. Bottom of the hole is dirt. Runs along the wall. (Basement walls/foundation are brick.) I assume there was once a coal-burning furnace (or some other part of a coal heating apparatus... maybe storage?) anchored there, but whatever it is is long-gone. It's just a hole. It does not collect water or anything wacky -- just bugs and dirt as far as I can tell. Right now, I have a piece of wood laid over the hole so no one (okay, mostly me) falls into it. But it's part of the area that I use for working out, and the space would be more useful if there wasn't a hole in the floor covered up by a board.

I'm thinking of filling the hole mostly with gravel, and then getting a single bag of some sort of cement to mix up and smooth over the top inch or so. Is this an okay idea? Or a terrible idea? Will this work? Will it cause problems I'm not thinking of? Is there something else I should do instead? If this is an okay idea, recommendations about actual materials? (I know zilch about cement or anything in that realm.)

I'm not at all concerned about it looking nice -- as noted, this is a 125-year-old unfinished basement. And if I'm successful, it'll eventually be covered by horse stall mats or some other type of workout flooring (I just have some carpet remnants down there right now). I literally just want to fill the hole so no one falls in it. Anyone have thoughts for me here?

[lthenderson]

It really depends on where you live, soil types and if there is any movement in the foundation walls relative to the existing concrete. Filling it with mostly gravel and topping it with concrete would be a suitable fix if everything is stationary but with a few caveats. First, I would pour it closer to three inches thick so that if someone were to roll across it with a dolly holding a heavy appliance, you won't crack the concrete. Second, I would put an isolation barrier between it and the outside wall to allow for movement of the foundation without destroying the interior concrete patch.  You can get a small roll of isolation barrier at all DIY type stores.

[dclarke1]

I had a similar thing in my basement. I ended up using the hole as a point to suck the radon out from under the slab and shoot it out the wall with a small radon fan. Not sure if radon is an issue in your area.

Anyway once I had the pipe secured in the area, I poured just plain concrete that you mix up out of a bag. Get it at Home Depot or something. Would work the same if you were just trying to fill the hole up.

I agree with lthenderson that you probably would want it a few inches thick.

Not sure if you are looking for a tight seal at the edges, but if so you may consider concrete with hydraulic cement.

At the end of the day you can't mess it up too bad because if you want to change it you can easily break it out and try again. Well worth trying to do yourself.

[Lucky Recardito]

Thanks, both. This is useful info. I'm in Chicago, with soil that's a mix of midwestern clay and sand (we're about a mile from Lake Michigan). Radon isn't a big concern to my knowledge -- I don't know anyone local with that issue in their house (but interesting thought about using it as a vent...). Basement floor is only about 3 feet below grade. Thanks for the tip on the isolation barrier and cement thickness. I shall continue mulling and hope to knock out this project this summer....

[Fishindude]

I'd fill the whole thing with bag mix concrete and be done with it.   One bag of concrete will fill approx. 1/3 cubic feet of area, so measure length, width, and depth of hole and purchase adequate concrete.
If it exceeds more than a few bags, I'd probably partially fill with some compacted dirt or gravel to save a couple dollars.

[zolotiyeruki]

Standard basement slab thickness is 4", I believe.  If it were me, I'd do 4" of concrete on top of tamped gravel.

[Sanitary Stache]

Your description makes me think of the hole I found in my basement. Mine was mostly covered over with concrete and had just one hatch remaining.  The hatch has a bunch of pipe set in the concrete across it, so it looked like a prison cell.  I was convinced some monster was going to come slinking out of it for a few days, then I calmed down.

Most likely explanation I found was that it was used to provide combustion air to an old coal furnace.

[Lucky Recardito]

TY, all!

(And yes: high probability that a monster lives in that hole when I'm not looking...)