Concrete floor in barn

[Brno8x57]

I’ve read the guide to concrete floors and have poured a driveway many years ago. I have 2500 square foot horse barn that has been used as a shed for decades. Dirt floor mostly; so lots of dust kicks up. I would lime to turn it into a garage for working on my motorcycles and other projects. Unlikely a car will be in there without making new doors and putting down a 200 foot long driveway of sorts.
With costs these days I want to try and limit $$.
Since it’s a covered barn do I need gravel base layer?
I am planning on a 4 inch pour with 12inch footers.
Should I remove enough base layer so top of slab sits at current floor height? 2x4 wall studs sit fully above floor
Rebar?

 

[ConCretin]

Curious about the 12" footers?

It's hard to say what the new floor elevation should be but the existing floor height seems like the logical place to start.

With regard to base material, this is going to be a bit controversial but if the existing soil is stable, there is no need to replace it. In geotechnical terms, the loads imposed by a residential slab on grade are quite light and even moderate quality materials can easily support them. The base just needs to provide uniform support. It's not a bad idea to have a couple inches of granular material to act as a capillary break but it's not necessary especially of you put down a vapor barrier.

Before you spend money on rebar, it's worthwhile to know what function it performs in a slab. It doesn't make the slab stronger i.e more resistant to cracking under load but it does hold cracks together if and when they occur. It's the same for wire mesh. It's not very cheap insurance.

 

[billconner]

If inside an existing foundation I too don't understand footers.

Clear span over or interior columns?

If the soil is compacted from a lot of years, I agree that gravel base probably not necessary.

I'd certainly want too of slab below underside of sill plate.

Considering a vapor barrier or insulation?

 

[Brno8x57]

Barn isn’t insulted so I was going with no insulation for the floor. Do I need a vapor barrier?

barn is clear span so no columns. One big floor.
So no footers and no rebar is what I’m hearing.

I can remove top 2-4 inches of soil so concrete slab surface is just below horizontal wall plates or just pour on top of current surface so concrete slab will be 4 inches above the current horizontal wall plates?

Is either better?
Any other suggestions

 

[mike93lx]

Barn isn’t insulted so I was going with no insulation for the floor. Do I need a vapor barrier?

barn is clear span so no columns. One big floor.
So no footers and no rebar is what I’m hearing.

I can remove top 2-4 inches of soil so concrete slab surface is just below horizontal wall plates or just pour on top of current surface so concrete slab will be 4 inches above the current horizontal wall plates?

Is either better?
Any other suggestions

Do not put wood in the plane of the concrete and make sure any wood touching it is pressure treated.

 

[ConCretin]

What are the barn walls currently bearing on? Is there an existing foundation? As has been mentioned by others, I'd want the concrete at or below the wall plate.

A vapor barrier blocks water vapor from the soils from migrating through the concrete into the building. While I'm guessing your barn isn't super tight and you probably wouldn't notice the difference, it would help protect metal items stored on the floor. 10 mil poly is relatively inexpensive and effective.

I wasn't trying to talk you out of rebar but since you mentioned trying to minimize cost, I just wanted you to know what you were getting for your money. Welded wire fabric performs the same function for less cost. It's primary disadvantage relative to rebar is that it's less rigid and therefor harder to support. If there are any question about the stability of the base, it might be a good option.

 

[billconner]

Very in favor of vapor barrier in most all cases.

Not recommending it for you but I'm thinking for a slab I should put in to use fiber mesh in place of rebar or welded wire. It would only work if base is stable.

 

[1320stang]

Pics of inside wall of barn? What kind of door openings? Would new slab be at the same elevation at the bottom of door?

My dad built a 80x120 Morton in the 80's with a gravel floor, he poured concrete in sections as he could afford. I'd forget the foundation and just put #3 @ 36" o.c and call it good.