CMU wall over existing slab

[kaisersoze]

The Arch wants to place 10'tall 4" & 6" cmu walls (ungrouted, interior) over an existing 4" slab. I am apprehensive even though the slab pics seem to indicate a decent condition of the slab. Am I being too conservative?

Kaiser

 

[hokie66]

Probably. CMU partitions are often built on existing slabs without adverse affect. The load spreads through the slab, so you will have a strip at least 10 or 12" wide resisting the wall load. You need to make sure the wall is braced at the top, and can span vertically between the slab and top bracing.

 

[SLTA]

Hokie's response assumes that the slab is still fully supported by the earth below it. You'll want to do a test pit at the location of the wall to ensure that the soil hasn't settled away from the slab. You could always cut the slab at that section and pour a new thickened slab under the wall. Yes, it's partition, but it will likely end up taking some of the load, and 10' of wall ain't light, either.

 

[kaisersoze]

Thanks fellas. I think I am going to have them rip out the existing slab, replace with a 5" slab and have them put the cmu on the new slab. Usually I use thickened slabs but there are too many walls if I go with 4" slab and thickened slab, that will just make things difficult in the field.

Kaiser

 

[nhstruct]

I just had a similar situation, Typically I don't like CMU walls on slabs less than 6". We showed on our plans that new hunched slabs at CMU wall locations, but made a note that the contractor to verify the thickness of the existing. slab. basically if we find the slab is about 6" or greater than we will let them dowel into the existing slab rather than but in a hunched slab or a strip footing.