Slab/Foundation Questions

[Shuck Grass]

I recently tore my shop down, I left the slab. It was a traditional stick build so to say. My new building is a prefabricated metal building. I am raising the elevation of the new slab 3’. My new building is the same size as the old. I was planning on pouring footer over the existing footers and hauling in sand over old slab and getting the compaction as required. Basically encapsulating the old slab. Is this the best way to do it, or remove the old slab and start fresh? Open to any ideas. Thanks

[ericm]

I’m an S.E. and have used a similar design on several projects. I’d recommend punching some holes in the old slab to avoid trapping water and using an angular aggregate (limestone preferably) in lieu of the sand.

[Dave A]

Was the footer and slab poured together or do you have block on top of footer and the slab poured inside the block ?

[Rip Bass]

I have plumbed up a ton of slab houses with the plumbing in the floor. That said, the very best,hardest fill I’ve seen is compacted screenings. I can’t help with the pouring question.

[Shuck Grass]

Was the footer and slab poured together or do you have block on top of footer and the slab poured inside the block ?

Original slab was poured together.

[ECobb91]

I’m an S.E. and have used a similar design on several projects. I’d recommend punching some holes in the old slab to avoid trapping water and using an angular aggregate (limestone preferably) in lieu of the sand.

this. I’m not a structural engineer but a highway engineer. It’s very hard if not nearly impossible to get proper compaction with sand. We can’t even meet compaction requirements using sand on simple sidewalk jobs. All sand is good for is drainage. But any vibration moves and shifts the sand so your bedding material will fail over time. As stated above go with angular stone (I.e. subbase material or crusher run used for sidewalks and roadway bedding). angular stone will lock into place during compaction. Also use water when compacting to keep the dust down and it helps get the fine material between the angular stone to fill voids. You also don’t want rounded stone or river cobble as they also don’t lock into place. Think of the parable of the man who built his house on sand. Same concept but with construction in mind.

[Dave A]

I'm no engineer but i'd say go ahead and pour your footers with at least two rows of rebar drilled into original footer about a foot apart and with 3 rows going horizontal making a cage. Not sure why it would be necessary to fill between footers, if i understand correctly the building will be sitting on the footer. Also i wouldn't use anything less than 3500 psi concrete.

[bhjr.]

Washed 57-67 stone over old slab and you're good to go. This type of stone needs no compaction and will bear the load.