Quick Answer: What Thickness Plastic Under Concrete?

What kind of plastic do you put under concrete?

The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil. All Americover Vapor Barriers are composed of virgin polyolefin resins and offered in 10 mil, 15 mil, and 20 mil.

Should you put plastic under concrete?

A concrete vapor barrier is any material that prevents moisture from entering a concrete slab. Vapor barriers are used because while fresh concrete is poured wet, it’s not supposed to stay that way. It needs to dry and then stay dry to avoid flooring problems. This is why a vapor barrier under concrete is essential.

Do I need a vapor barrier under my concrete slab?

Water vapor will always move from a high relative humidity environment below the building into an area of low relative humidity – even through concrete. That’s why nearly every expert in the concrete industry recommends a belowslab vapor barrier to stop the vapor drive of water upward and into your building envelope.

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What can I use for vapor barrier under concrete?

The use of a vapor barrier (more accurately termed a vapor retarder), having a water vapor permeance of less than 0.3 perm is frequently used to retard the flow of moisture through the slab. These vapor retarders are typically polyethylene or polyolefin sheeting materials.

Do you need rebar for 4 inch slab?

No, you do not need rebar for a 4inch slab of concrete on grade. A 4inch-thick slab cast on the ground and in permanent contact with it will float and rebar is not required. Rebar is recommended on concrete measuring 5 – 6 inches thick.

Can you pour concrete directly on dirt?

Long story short, yes you can pour concrete over dirt.

Is gravel needed under concrete?

Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn’t drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.

Is sand a good base for concrete?

Pour concrete over a solid, well-drained base



of sand or gravel over clay and other poorly draining soils to provide even support.

What kind of insulation goes under slab?

Two of the rigid foam insulations most commonly used below grade and under slabs are expanded polystyrene (EPS) and extruded polystyrene (XPS). Although both are closed cell insulations, they perform very differently over the long term.

Why do they put Styrofoam under concrete?

They reduce the effects of soil movement, decrease the amount of concrete required, and have thermal insular properties making them a cost effective component for any home, building or complex. In traditional slabs, the bottom of the slab uses footings based on concrete beams which require extensive digging.

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Is concrete a vapor barrier?

Lots of vapor moves by air movement, not a heck of a lot of vapor moves by vapor diffusion. The concrete slab is the air barrier, and the ripped and torn and punctured polyethylene sheet is the vapor barrier. It’s that Fick’s Law thing.

Is Tyvek a vapor barrier?

No, DuPont Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.

What type of gravel is used under concrete?

Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) is one of the best base materials for concrete flatwork.

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