Our 100-year-old home's basement floor is very thin (1/2"?) concrete. A friend once called it a "rabbit floor", only intended to keep critters from burrowing up into the basement 🙂 It is uneven, cracked in places, and it appears to have been poured directly onto the dirt.
The basement walls are also concrete, about 7' tall (5.5' under grade, 1.5' above). They aren't perfectly smooth and flat; it looks like they may have been poured into trenches dug into the ground, without forms, or perhaps someone simply did a very rough job of skim-coating them in the past…
The basement walls seem strong: the house doesn't show any signs of settling problems over the years.
I want to smooth out the floor and make it nicer. I'm envisioning covering it up with more concrete and/or leveling overlay. I don't intend to finish the basement because it sometimes gets wet in the winter and taking care of the water intrusion is far down on my list of home improvements 🙂
The water issue is seepage from the joints between the basement walls and the floor. It usually is just dampness, but some years I'll get small puddles (a foot or two long) that last a day before drying. As far as I can tell, these puddles are formed by the joint seepage and not from water coming up through the floor. There is a drain along one wall, but never enough standing water to make use of it.
So, my questions:
- Is it OK to pour new concrete over old? Do I need to prep the existing stuff first?
- What thickness of concrete would be appropriate as an overlayer? I don't want the new concrete to break away from the old…
- Should I put some sort of water barrier between them?
- How do I interface the new concrete to the walls? (Expansion joint, etc)
- Is this just a bad idea??
Oh, I forgot to add:
There's a washer/dryer in the basement. Other than that, I'll use it as a shop and for storage.
Best Answer
Get a contractor to take a look at it for sure. But I suggest to you that you will really need to rip out all the old concrete, re-prep the substrate and level it before putting in any new concrete. This will be the only good way to get a decent long lasting floor. Make sure to include heavy gauge wire mesh (5x5 or 6x6 inch grid) and re-bar if called for. When the slab is the proper thickness (3.5 to 4.5 inches) this can really help keep it together in the case cracks develop.
While you have it all opened up you should strongly consider adding drain lines along the bottom of the foundation over to a sump in one corner to help divert water from coming in on your new floor.
The type of patch up fix you asked about is really a waste of money because it is unlikely to last. Especially if you intend to use it for a shop floor.