Weird Concrete

[MiketheEngineer]

Scenario -

Old house - at least 70 years - still has some knob & tube wiring

While excavating for an addition - back foundation wall about 7' tall was exposed. House appears in good shape - no wall cracks, etc.

Concrete foundation wall looks like a real "lean" mix of cement and 1'' to 2'' rock about 8'' thick and 7' tall and might have just been packed into place. Possibly - no water was used.

Bottom half - you can literally pick the rock out with your finger. You could go through it with a claw hammer in a few minutes. Top half that was above grade looks like it was covered with a cement over coat. Not sure what is behind that.

On the inside (basement) - it appears that an extra stem wall wall about 6'' thick and 4' tall was poured. Why - I do not know.

My questions:

Any idea what I am looking at....

Any suggestions on repairs other than repouring the whole wall - which is what I have already suggested.

Thanks for any help...

 

[JAE]

Can you post some pictures? See the Step 3 below the submit box via Engineering.com.

 

[msquared48]

If there is no observable distress in the existing wall, why not just extend the foundation for the addition down locally as needed so the wall sees no additional lateral load.

If the existing wall sees more vertical load, you might want to pour a new wall next to it and bear on that if possible to avoid having to remove the existing.

Mike McCann
McCann Engineering

 

[MiketheEngineer]

Thanks for the help

No pictures available.

And yes we have discuessed pouring a sister wall next to it to carry a minimal load from the addition. Probably the cheaper solution although I worry a bit about the future.

 

[rday]

Mike,

The extra interior stem wall sounds like something I've seen when basments have been retrofitted to older homes, usually without engineering.

I would imagine the entire wall is as youe descibe with the coating applied to the visible portions.

Where is the house?

 

[MiketheEngineer]

Midwest - St. Louis

 

[dik]

Old rubble stone walls were often held together with mortar that had differing hydraulic properties. Some poor mortar without proper additives/impurities had little or no hydraulic cement and over the decades this material has leached out, basically leaving the lime and little or no strength.

Dik

 

[MiketheEngineer]

Sounds like DIK might have something there.

It looks like concrete - but you can pick it apart with your fingers.

Since we are pouring an addition anyway - customer likes the idea of a "full" basement. So - we are going to replace the wall with columns and beams.. Pretty simple and cheap. Just wonder what is happening in the other three walls??

 

[dik]

Very likely they have used the same mortar... best to take a gander.

Dik

 

[DRC1]

The top may have been a previous repair - dry packed concrete. Cement ans asand mixed, a touch of water and then packed inot the repair area. It is commonly used in underpinning, although I have never heard of such a thick layer. Sounds like a neat project.