Concrete Floors - Chime in

[AJP]

100 YO barn may come down one day .. if you think you might rebuild on the same spot then plan for some more footers before you pour. Obviously the right mix , temperature, the time to your site, the curing time and conditions are important - although with a roof already on I imagine it won't dry too quickly. I also am a big fan of running pex for future heating anytime you pour (as well as proper drainage) vibrating is good to get the air out of the mix and settle low slump around the rebar properly.

 

[bkfj40]

If you're talking about a vapor barrier below the slab, that's not true. A vapor barrier below the slab actually inhibits ideal curing because it prevents water from hydrating out the bottom of the slab. Since it can't hydrate out of the bottom it forces the water to hydrate up through the top of slab which results in uneven curing from top to bottom and curling as I mention previously. ACI and any other authority on concrete recommends against using a vapor barrier where you are not applying vapor sensitive floor coverings or slabs in humidity-controlled areas. IMO, a slab in a barn is the poster child case of where not to use a vapor barrier.

Some bad info elsewhere in this thread, but this info is spot on. You get what you pay for. Free advice is worth exactly that. When I did my pole barn/garage floor, I used 6x6-w2.9xw2.9 wwf. I tied the pex to the mesh at 12" o.c. I stopped the mesh at the saw cut joints and used dowel baskets. I went with a 5" slab and took pictures of the pex layout for future use.

To the OP, you never mentioned where you are building. Find a contractor to help or an engineer. Look at what they have designed or placed that is at least 2 years old. I have designed over a million square feet of concrete slabs, but it all comes down to how the contractor puts them in and what the redimix plant supplies.

 

[AJP]

and took pictures of the pex layout for future use

Excellent idea! Using a Ramset when you are not exactly sure where the pex is a crapshoot at best and it is nice to know what zones/loops you're heating without trial and error

 

[bigbrowndog]

If you're talking about a vapor barrier below the slab, that's not true. A vapor barrier below the slab actually inhibits ideal curing because it prevents water from hydrating out the bottom of the slab. Since it can't hydrate out of the bottom it forces the water to hydrate up through the top of slab which results in uneven curing from top to bottom and curling as I mention previously. ACI and any other authority on concrete recommends against using a vapor barrier where you are not applying vapor sensitive floor coverings or slabs in humidity-controlled areas. IMO, a slab in a barn is the poster child case of where not to use a vapor barrier.

Mate, It is a requirement here under the building code where I live, paths, drive ways and garden sheds are exempt. It is also a requirement to tape the joins in the plastic
membrane. Seems you have different ideas over there. As for it not being able to hydrate properly, what stops the sand/ crusher dust /soil absorbing the water from the concrete and changing the cement/water ratio reducing the strength of the mix? cheers

 

[Rookie2]

As for it not being able to hydrate properly, what stops the sand/ crusher dust /soil absorbing the water from the concrete and changing the cement/water ratio reducing the strength of the mix? cheers

Be aware first off that most concrete mixes contain a significant amount more water than is needed for cement hydration. Most residential type mixes probably have a water/cement ratio in excess of 0.55, when it only needs about 0.25 for hydration. The excess water is in order to obtain a certain level of workability for placement.

Having said that, you are correct in that you don't want the water pulled out of the concrete to quickly which is why you put curing compounds, plastic sheeting (burlap sacks in the old days) on the top of the slab to prevent water from evaporating to quick. If you had a hot and dry sub-base it wouldn't be a bad idea to pre-soak it, but at the end of the day it's a contained area once the concrete is poured and not subject to air so it has a limited capacity to pull water out of the mix to quickly IMO. At least I've never heard of this as being a problem.