Uneven basement floor

[lzr1621]

Hi,
Are bowing or sagging in basement floor any indication of a foundation problem or other structural problems? I was shown a 1925 house where all residential floors look level, but the basement floor has bowing or sagging as you walk along its long side (i.e. as you walk parallel to the beams). I was advised elsewhere that basement floor is poured at a different time, so it should not be related to structure, I want, experts, your opinion on this.

 

[BAretired]

Basement floors are normally grade slabs which are separate from the building foundation. Grade slabs may heave if the subsoil swells due to an increase in moisture content; alternatively, they may settle if the subsoil has not been adequately compacted, is eroded or dries and shrinks. Uneven basement floors are usually not an indication of foundation problems.

BA

 

[Tmoose]

What is the foundation wall construction?
Are the walls visible, and crack free?

Some tapping with a hunk of 4X4 or a hammer may reveal a thin floor's hollowness due to settled subsoil.

 

[oldestguy]

One problem that may or may not have occurred, but probably not for an older house. That possible problem is erosion of soil through open graded stone as part of a drain system to drain away ground water usually via drains near the foundation. Open graded stone is gravel, about one stone size only, with large void spaces. That situation does not filter out soil as water may pass going through it on its way to a sump pump. In these cases floors may settle and nearby foundations also can settle. One obvious sign of this is when a large delta forms at the discharge of water from a sump pump. Proper filtering the the water by not only with a filter on the pipe, but also using the proper drain material around the pipe and wherever water is collected, as under floors. Even today architects and some engineers think that open graded stone backfill and underfloor fill is the way to go. Carrying any amount of water that may also erode soil can have these installations fail early on. That proper filter for most soil types is ASTM C-33 concrete fine aggregate (concrete sand).

 

[lzr1621]

Hi, BAretired and Tmoose,
Thanks for your input. The foundation walls are masonry, the basement is finished, so I can't see cracks if any, but I presume there must be cracks in the floor since solid concrete slag must be flat, am I correct? Can the issue with basement floor/subsoil present a problem other than annoyance?
LR

 

[BAretired]

If the slab movement is recent, there could be a problem and it should be investigated. If the movement occurred years ago and has not moved recently, it is unlikely to present a future problem other than annoyance.

BA

 

[lzr1621]

Thanks

 

[HouseBoy]

"solid concrete slag must be flat"
If by that comment you mean that concrete must be flat because it is placed while fluid, that is not correct. A concrete basement slab that was placed in a house in 1920s is often very uneven so, current "out of level" or uneven conditions might be misleading.
Also, I find that cinders were often used for basement slab leveling back in the day.

It's tough to say without seeing more but I would not normally expect that an uneven concrete basement floor alone is a sign of a foundation problem. Usually I'd expect to find distress in the floor above. With that said, I often find that interior footings in houses of that age are sometimes substantially undersized (or practical non-existent) and THAT will lead to uneven conditions but they should materialize in the floors above.