Quick Answer: Should You Put Plastic Under A Concrete Slab?

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 gravel 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.

Can you pour concrete over dirt?

With proper preparation, however, it’s possible to pour a slab on clay soil without encountering these problems. Clear and level the area where you plan to pour the concrete slab. … Create a barrier between the concrete and the soil by pouring a 2-inch to 4-inch layer of sand or gravel into the bottom of the frame.

Why is my concrete floor always wet?

There are a couple of reasons why your garage floor may be getting wet. The most common is condensation — AKA sweating garage floor. When relatively warm, moist air comes in contact with a very cool concrete slab, the cold temperature of the concrete will cause the air that comes in contact with it to cool.

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.

Can water come up through a concrete slab?

The easiest way for water to leak through concrete is to come in through any cracks in the floor. Ignoring cracks in your concrete floor—even those as small as 1/8 inch wide—is like inviting water into your home. … These materials come pre-mixed or in concrete-like form that must be mixed with water.

How do I reduce moisture in my concrete floor?

Methods Used to Stop Moisture in Concrete FloorsLow-permeance Vapor Barrier or Retarder. A Low-permeance vapor Barrier or retarder can effectively keep below-slab moisture from reaching the flooring system. … Allow Natural Drying of Concrete Slab. … Keep Excavation Free of Water.

How do I know if my concrete floor has moisture?

Spread out each plastic square flat over a dry area of concrete. Tape along all four edges of the square with duct tape or other waterproof tape. Firmly press the tape to create a moisture-tight seal with the plastic and concrete. Use as many squares as needed to test all the main areas that may get flooring.

Should I insulate under my concrete slab?

Creating an insulation layer and a vapor barrier between the concrete slab and the ground beneath it is the best practice in insulating basement floors. The insulation barrier will help keep warm air in, and the vapor barrier will keep unwanted moisture out.

Should you put Styrofoam under concrete?

Putting styrofoam under the slab is fairly common here. If the base is preped and tamped properly, and the correct concrete and wire is used, you will crack no more or less than you would without the foam.

What is the purpose of a vapor barrier under concrete slab?

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 do you put under a concrete slab?

Just scrape off the sod and topsoil and add gravel fill if needed. If you have clay or loam soil, you should remove enough to allow a 6- to 8-in. layer of compacted gravel under the new concrete.

What kind of insulation should I use under concrete floor?

Insulating a solid ground floor below the ground bearing concrete slab can be done using either PIR insulation boards or EPS insulation boards. EPS can be a cost-effective alternative to PIR for floor insulation, and the same thermal performance can be achieved with increased thickness.

What is the best base for 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.

Is a vapor barrier necessary under a concrete slab?

Actually, no. Air barriers need to be continuous and free from holes, but vapor barriers do not need to be. 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.