pouring concrete

[Justin Caradoc]

I live in a 1920's 3-story row house and my current work area is the basement, which is unfinished. I would really like to put a concrete floor in but I am not sure my idea would work. The ceiling is about 7 feet tall but with all the ductwork it makes it 6.5 feet tall in spots. I don

[John B]

Dig out a corner and see where the foundations are, and how deep. You can then make a decision on whether to dig it out 2" or deeper, if you dig it deeper and lower the floor it will give you more headroom

I live in a 300 year old famhouse and the bulding is made of cob (Mud and straw mix rendered) which sits on the ground, no foundations as such, we removed the old wood flooring which was sitting on the earth, dug out at least 6" put in a damp proof membrane and concreted it, This was approved by the building inspector and no more worries about the floor

[Justin Caradoc]

thanks that help :)

[rstegman]

One idea is to leave a foot or two around the edges at the foundation, and then you can dig down till the lowest stoop down spot with the duct work is seven feet with your full thickness concrete.

I am not an engineer, but you might dig trenches to the wall and add supports in one foot sections, for instance, to support the wall and do that under the main rocks, then add more support trenches between until the whole wall all the way around is fully supported.
A third idea, that would require engineer's guidence, would be to put temporary posts all around, and replace the foundation with blocks and concrete.
I think, though, is to leave a step of material near the walls and dig down everywhere else to give you the depth you need.

[ThomasPowers]

Make sure to put in the damp proof membrane under the concrete.

Also if the walls leak you might think of putting in a bit thicker pad and place removable pieces of wood along the wall sloped so they tend toward a sump; When they are removed you have a built in drain keeping water from getting up onto the floor. My parent's house was done that way and they never had any water problems---just don't put things touching the wet walls!

[Sask Mark]

Some exploration to see what nature of the existing footings are would be your best option. Once you know that, you can go from there. There might be a spread footing type of foundation below your basement walls. If this is so, you can dig deeper, but don't undermine the footings.

If you don't have any cracks in the brick and stone walls, you are in quite stable soil conditions and your foundation is solid.

To solve the moisture issues, you can dig down and place a bed of compacted granular. Ideally, you would have a sock-wrapped weeping tile running in a grid pattern at the base of the granular carrying the water to the sewer system. Then place some heavy poly over the granular and pour the concrete over that. Make sure you have an isolation joint between the footins and the slab as you want the slab to float independantly. That way, you won't affect the footings if you get some heave or slump in your slab.

[Steve Sells]

I hate to be the bringer of bad news, but 4 inch is the min reliable thickness to pour, 2 inches wont last. adding mesh helps but you still should have at least a 4 inch thickness

[Paul B]

How deep is it in the ground to start with? How far up the outside walls does the backfil come? There might not ba a footing at all. Dig out a spot and see if there is or not, then we can go from there.

edit: I should have read all the replies first before opening my big keyboard!

[divermike]

As I am a code enforcement officer, I would like to pipe in here, if you take an imaginary line from the bottom of the footing, at 45 degrees downward on both sides of the footing, this is called the cone of compression, this is the soil that the load from the house is distributed into, never, never,never, disturb this soil over large areas, if the footing is deep enough below your current soil level for you to excavate, I would suggest looking into the floating slab drainage system, this is a great system to get rid of moisture. As the other gentleman said, the slab needs to be a minimum 4" to keep from cracking, and this should be properly reinforced. Good luck.