Quick Answer: Should You Put Plastic Under Concrete?

How do you prepare the ground before pouring concrete?

Preparation is the most important aspect of pouring a concrete slab.Dig the ground down to the proper depth.

Smooth out the ground with the flat side of a rake so that you have a level surface.

Tamp the ground with a hand tamper or mechanical tamper.

Pour 2 inches of small, rounded gravel for additional drainage needs..

Is Clay a good base for concrete?

The clay can compress under the weight of the concrete, causing the slab to shift or sink over time. It also can leach moisture from the concrete itself, resulting in uneven curing and a brittle base. With proper preparation, however, it’s possible to pour a slab on clay soil without encountering these problems.

What type of gravel goes under concrete?

Backfill beneath concrete flat-work along foundation walls should be accomplished with a granular material that is uniform in size. Some fill materials, such as round stones like pea gravel, tend to be self compacting. “I recommend open-graded granular material be used,” says Tull.

Can moisture come up through concrete?

Moisture Still Present Concrete is porous by nature and, even though the moisture near the surface of the concrete evaporates as it cures, moisture from below the concrete or within the concrete will tend to osmotically migrate up through the concrete capillaries, to escape through the path of least resistance.

Should you put plastic under concrete slab?

Recently, though, research has shown that the old traditional layer of 6-mil Visqueen (polyethylene plastic) under the slab is seldom effective for two main reasons: Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through.

Is a vapor barrier necessary 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 you pour concrete directly on dirt?

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

What is difference between cement and concrete?

What is the difference between cement and concrete? Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement.

Can water come up through a concrete slab?

YES, water around your foundation can come up through the concrete floor and can leave any material on its way soggy and damaged.

What is the best insulation for under a concrete slab?

For under-slab applications, the rigid foam insulation typically should be installed over a gravel base, with a poly vapor diffusion retarder between the gravel and insulation. Additional insulation is applied along the edges of the slab, because that is a primary surface for heat loss.

Do you need wire mesh for 4 inch slab?

No, they do not. Larger projects or slabs may need steel reinforcement to provide support or extra strength. Wired mesh can also help resist cracking. However, not every piece of concrete necessarily requires that extra boost.

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. … Only closed-cell SPF can be used in a subslab installation; the open-cell foam does not have adequate compressive strength.

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.

How many inches of gravel do you need for a concrete slab?

Construct the form with 2×4 or 2×6 lumber and secure in place by wood stakes and deck screws. Excavate the slab area to a depth of about 7 inches, allowing 3 inches for a gravel base and 4 inches for concrete.

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.

What can I use for vapor barrier under concrete?

Use a low permeance vapor retarder to protect floor slabs that will be covered with moisture-sensitive floor coverings, adhesives, and coatings. … Include a capillary break of granular material below the slab. … Consider using concrete having a w/c not greater than 0.45 to hasten slab drying time.More items…

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.

Will concrete cure under dirt?

Assuming that the concrete was mixed in the proper ratio and poured in an acceptable temperature environment, soil backfilling will not harm the curing concrete (assuming no mechanical stresses or insults were done to the curing concrete; that is, no fractures, scours, washouts or chemical exposure).

Is wire mesh better than rebar?

Considering the support constraint, rebar is undoubtedly stronger than wire mesh. Several constructors consider rebar for domestic jobs. For thicker driveways and locations that involve greater traffic, rebar is always a good option to consider.