Should You Put Plastic Under Concrete?

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 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.

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

4 inchesA hand tamper is sufficient for packing gravel, but a plate compactor makes the job much easier, especially when preparing a large area such as a patio. Excavate the soil to a depth of 8 inches, allowing 4 inches for the gravel base and 4 inches for the concrete slab.

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 best to put under concrete?

Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.

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.

Can you put a vapor barrier over concrete?

Therefore, in high-humidity areas, moisture will move to a relatively low-humidity area, even through concrete. Therefore, because concrete is porous, it’s a good idea to install a vapor barrier over your concrete subfloor before installing your flooring.

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.

How do you prepare the ground for a concrete garage floor?

Good ground preparation starts with removing the topsoil. Then, if the soil has not previously been “disturbed” (i.e., dug up), a four-inch layer (minimum) of gravel or stone should be added. (Soil that has been dug up before should be compacted.) The gravel or stone also needs to be compacted.

Is quikrete as strong as regular concrete?

Quikrete fast setting concrete is just as strong as regular concrete. Concrete gets its strength from a chemical reaction that occurs over time during curing. After it’s had time to cure, which usually take 28 days to complete, Quikrete can reach strengths up to 5000 psi.

Can you pour concrete on plastic?

You can build a framework around the concrete slab with lumber, PVC pipes, or rebar to hold the plastic sheeting. Another method to prevent discoloration is to place dry straw directly onto the concrete, then put the plastic on top of it. Wet the concrete, then place the plastic sheeting over it.

Can you pour concrete directly on dirt?

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

What is the purpose of 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.

Can I use pea gravel under concrete?

If you use pea gravel beneath a patio, take a few simple steps to ensure the stability of the base before setting your surface stones, pavers or bricks. Click to see full answer. … It should be ok to pour concrete over your gravel walk although you might want to give the concrete a little more depth along the sides.

How many bags of concrete do I need for a 10×20 slab?

A 60-pound bag yields . 017 cubic yards, and an 80-pound bag yields . 022 cubic yards. For a 10 x 10 slab, you would need 77 60-pound bags or 60 80-pound bags.

How strong is 2 inches of concrete?

How strong is 2 inches of concrete? A common bag of concrete, for example, may have a compression strength of 4,000 psi, based on a thickness of 2 inches after it has set for 28 days. Other concrete may have a compression strength of only 550 psi.

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.

What is the hardest concrete mix?

A strong concrete mix would be something like 1:3:5 (Cement, Sand, Coarse Gravel). In this case, both the sand and gravel are the aggregate.