Hey cement folks, need tips on how to prepare the soil for a shop slab.

[Chuck K.]

I am going to attempt to build a 40'x60' metallic shop. The existing 24'x24' 2 car garage is going to be torn down and hauled off first part on next month leaving only the cement slab.

My plans is to remove the top soil around the garage so decomposing grass cannot create any voids. Next haul in enough quality fill dirt to raise the pad ~2' over the existing garage floor feathering it out 4' on all sides to grade.

Set the forms haul in sand, dig beams, will have to find out how many demensions, lay wire mesh and rebar. Anyone dug the beams with a small B/H? Hmm could maybe justify (in my mind anyhow) getting a B/H for the
L3400 .. I have a buddy who is far more knowledgable than me who is going to help.

Is pouring a slab over an existing slab a good idea? I would hate to have to break it all out and haul it off.

Thanks for any advice... Chuck

 

[crbr]

Good luck on your project.

 

[flusher]

I am going to attempt to build a 40'x60' metallic shop. The existing 24'x24' 2 car garage is going to be torn down and hauled off first part on next month leaving only the cement slab.

My plans is to remove the top soil around the garage so decomposing grass cannot create any voids. Next haul in enough quality fill dirt to raise the pad ~2' over the existing garage floor feathering it out 4' on all sides to grade.

Set the forms haul in sand, dig beams, will have to find out how many demensions, lay wire mesh and rebar. Anyone dug the beams with a small B/H? Hmm could maybe justify (in my mind anyhow) getting a B/H for the
L3400 .. I have a buddy who is far more knowledgable than me who is going to help.

Is pouring a slab over an existing slab a good idea? I would hate to have to break it all out and haul it off.

Thanks for any advice... Chuck

Any reason you can't salvage the existing slab and just add on to it to get the size you want?

Compacting fill dirt can be expensive. Need to build up the thickness in layers, and water and roll each layer, etc.

 

[bamatoolmaker]

I asked a concrete man your question awhile back.I was told that you can pour a new floor over an old one.The only thing you need to do is drill holes in your slab and drive in rebar an inch or so below the top of your forms.

 

[BillyP]

Is pouring a slab over an existing slab a good idea? I would hate to have to break it all out and haul it off.

Thanks for any advice... Chuck

If I'm understanding you right the existing slab will be covered with 2' of fill? If that's the case, yes, you can pour a slab over a slab without any problems. You can pour a slab directly over an existing slab as long as you put a thin layer of sand between the two. I went through this several years ago when I poured another slab over my existing carport.

 

[BillyP]

Chuck, there's one thing I'd suggest you do for sure. I don't know how the humidity is where you live but around here a concrete slab can sweat to the point of being sloppy wet. Put some Visqueen (black or clear plastic works too) down for a moisture barrier. The cost is next to nothing but the problem it solves is priceless.

 

[_RaT_]

Chuck, there's one thing I'd suggest you do for sure. I don't know how the humidity is where you live but around here a concrete slab can sweat to the point of being sloppy wet. Put some Visqueen (black or clear plastic works too) down for a moisture barrier. The cost is next to nothing but the problem it solves is priceless.

Vapor barrier a must. Use rebar, forget the wire mesh. Rent a plate compactor to compact the crap out of the fill. A plate compactor is not a plate vibrator. The compactor will weigh 500lbs maybe more and runs on a small diesel. Do it in lifts of about 8" or so. Soil mositure is critical to good compaction. #4 rebar spaced at 2' centers should be fine. Old slab should not be an issue with that much cover over it.

 

[Chuck K.]

Flusher, the old slab has settled and is too low, I am afraid of water coming in during heavy rains this is why I want to go up about 2’

The vapor barrier is definitely going in as I have seen the amount of sweat that can happen because of our high humidity here on the Gulf coast..

I will look into the plate compactor, and maybe even rent a small sheeps foot that is pulled behing the tractor to compact the soil..

Thanks for the input… Chuck