Should You Put Plastic Under Concrete?

Should you put plastic under concrete slab?

The sand layer cannot dry downwards by vapor diffusion because of the plastic sheet—it is a vapor barrier after all.

In fact that’s why we have it under the slab.

We want a vapor barrier under the slab.

** We want to prevent water vapor from coming up from the ground into the concrete slab..

Do you need a vapor barrier under a 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 below-slab vapor barrier to stop the vapor drive of water upward and into your building envelope.

What mil plastic should be used 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.

Can moisture come up through concrete?

Concrete’s porous nature means that water from under your home can seep up through your concrete floor, making it damp. This can cause issues with mold and mildew, especially if you have carpet or furniture on top of the concrete. … Sealing the concrete can help eliminate the dampness on your floor.

What is the purpose of plastic under concrete?

What is a concrete vapor barrier? 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.

How do you install moisture barrier under concrete slab?

Most exterior slabs do not need a vapor barrier. … In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. … The vapor barrier can be placed under the subbase, if the building is closed in when the dry subbase material is placed.More items…

Can you use spray foam under concrete slab?

Insulating under foundation and basement slabs using SPF (spray polyurethane foam) offers certain advantages over the more common method of using rigid foam board. … Two-pound foam. Only closed-cell SPF can be used in a subslab installation; the open-cell foam does not have adequate compressive strength.

Can you pour concrete directly on dirt?

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

Do you need rebar for 4 inch slab?

No, you do not need rebar for a 4-inch slab of concrete on grade. A 4-inch-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.

What is the best base for concrete?

The base course material, according to ACI 302, “Concrete Floor and Slab Construction,” should be “compactible, easy to trim, granular fill that will remain stable and support construction traffic.” ACI 302 recommends material with 10 to 30% fines (passing the No. 100 sieve) with no clay, silt, or organic materials.

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 type of gravel goes under concrete?

“Six inches of well-graded gravel or crushed stone material properly compacted will give good results,” said Mark Conrardy, a sales engineer manager for Wacker Corp., Menomonee Falls, Wis. When properly compacted, both native soils or imported granular materials can provide good support.