Concrete prep

[Mx391]

My shop is completely built, now I need to work on the prep work to pour concrete. Should have done a lot of the prep work before the shop went up, but I'm a newb.

I rented a skid steer and dug the dirt out to where I will have 4" or more of gravel with 4 or 5" of concrete. Is 4" of rock under concrete sufficient? I live in middle TN so clay is hard as a rock. Will 3/4" rock be ok compacted?

I wish I could post pics, but cant figure it out. Is there a special app I need to post pics off my phone? Thanks.

 

[SCATFEVER]

All of that sounds good, Thats what I will be doing in NY...

But ask a local concrete company for a quote and see what they plan to do.
This is a good free way of getting the way it should be done from a professional

 

[Mx391]

All of that sounds good, Thats what I will be doing in NY...

But ask a local concrete company for a quote and see what they plan to do.
This is a good free way of getting the way it should be done from a professional

I'm not wasting somebodies time just so I can do something myself to save money.

 

[johnnyradiant]

It doesn't hurt to ask a local that specializes in this. You don't have to dangle a carrot you won't be releasing. You can be up front and ask them the same question you posted here. Not everyone will want to have their time wasted but some will give you a simple answer to this question if you're not rude.

 

[Leaflessshadetree]

3/4" Rock with sharp edges and fines will compact nicely (hard clay does as well).
I had a couple inches (or less) of gravel that was my floor for a couple years. The contractor I hired wanted to do the gravel and compacting (pretty cheaply if I recall).
When they came to do it the gravel I had been using was too hard for the skid steer to dig out.

I would also recommend putting a vapor barrier. Are you thinking about insulating under the floor or heating it?

 

[NoPressure]

I'm not wasting somebodies time just so I can do something myself to save money.

Amen. That’s extra ******.

 

[brewchief]

Are you planning on placing the concrete yourself or hiring it out? If hiring someone they may want to do the prep themselves.

Sent from my SM-G965U using Tapatalk

 

[Copymutt]

I’d be real certain that is not expansive clay. That **** is used to split boulders the size of homes. I lost a slab to it.

 

[ConCretin]

As long as it is undisturbed, stable and free or organic material, you can usually place right on native soil. A 4" base layer isn't going to add anything structurally but it can keep the soils underneath from getting all churned up if you get some rain. Since you are under cover, this isn't much of a concern anyway. You'll be fine.

Give my Guide to Floor Slabs below a read for some additional thoughts as you go forward with your slab.

 

[machsnell]

As long as it is undisturbed, stable and free or organic material, you can usually place right on native soil. A 4" base layer isn't going to add anything structurally but it can keep the soils underneath from getting all churned up if you get some rain. Since you are under cover, this isn't much of a concern anyway. You'll be fine.

Give my Guide to Floor Slabs below a read for some additional thoughts as you go forward with your slab.

LL I know you have extensive concrete knowledge in both flat work and structural work. I loved your home build. Just amazing.

Here in Virginia and I assume up north where you are stone is always spec'd under concrete. Why do you suggest that the stone wont add any strength structurally and suggest to pour on directly on existing soils? I was a little surprised.

Not picking a fight just would like to hear your reasoning.

Sent from my SM-G960U using Tapatalk

 

[TractorJeff]

I'm not wasting somebodies time just so I can do something myself to save money.

Isn't that what you are doing here?
asking for advice but not expecting to pay for it?

 

[Lynden]

Here's some good information.

https://www.concretenetwork.com/concrete-subgrades-subbases/ -- other related topics are listed in the left margin

The proper way to design the slab is to have a local soils engineering firm do a soils test. The testing company will probably have a civil engineer on its staff who can design the slab structural section (subgrade+base+slab) and give you specifications for how the slab should be constructed.

 

[matt_i]

I would use the #57 washed stone, 3/4" nominal, rent a plate compactor to get the stone solidified.

Vapor barrier, 6 mil is good, 10 mil is better, overlap seams generously.

Reinforcing steel of your choice, I regard rebar placed on chairs and tied in a grid to be the best, and there's the general wire mesh hooked into place during the pour.

Determine how you'll cure the slab once its just-finished. Wet cure or curing sealer. Very important is to saw cut the control joints the next morning after the pour. 10-12' squares.

Avoid heavy machinery for 28 days and then enjoy.

 

[ConCretin]

LL I know you have extensive concrete knowledge in both flat work and structural work. I loved your home build. Just amazing.

Here in Virginia and I assume up north where you are stone is always spec'd under concrete. Why do you suggest that the stone wont add any strength structurally and suggest to pour on directly on existing soils? I was a little surprised.

Not picking a fight just would like to hear your reasoning.

Sent from my SM-G960U using Tapatalk

No offense taken machsnell. Let me try and clarify. While a thin base layer is often spec'd, it really isn't a structural element. A 4" layer of stone might distribute the load very slightly but a few inches of stone obviously isn't going support loads by itself. It just transfers loads to the soils below.

The primary purpose of adding a thin base layer is to provide a leveling course and to protect the native soils from getting churned up or rutted if it rains. I didn't mean to suggest that the OP pour on existing soils although it is perfectly possible to do so if the conditions are right.

It's more common that the existing sub grade is too low and base material must be added to bring up the grade. It's obviously important that this material be structurally sound but again, mostly in terms of providing uniform support.

it's a common refrain that the base is just as important as the slab, which is true but the base consists of all the soils under the slab - not just an added base layer. A slab doesn't care what kind of material it sits on - just that that material supports it adequately and evenly.

Edit: There are cases where a thin stone base is desirable to add a capillary break if the native soils are very wet.