Why do you put plastic under a concrete slab?
Why Do You Put Plastic Under A Concrete Slab? Why do you lay plastic under a concrete slab? Because the plastic sheet acts as a vapor barrier, the sand layer cannot dry downwards via vapor diffusion. This is because the plastic sheet is a vapor barrier. In point of fact, this is the reason why we have it buried under the slab.
How to protect concrete slab from soil?
So, you need to put a vapour and moisture barrier underneath a concrete slab and plastic sheets are a great option. The plastic will prevent moisture from the soil from permeating through a slab. It will also reduce the amount of water wet concrete sucks up from the ground when it is first poured.
Should I put plastic on top of concrete?
The plastic will help keep moisture from coming up, but also to keep the ground from sucking all the water from the concrete. If your contractor is good with concrete then he should have no problems with the finish with plastic. It will hold a little more water, but nothing thats major.
What is the best material to use under a concrete slab?
The most common material used under concrete slabs is polyethylene plastic sheeting with a recommended thickness of 15 millimetres. A vapour barrier should be made of high-performance materials capable of stopping moisture from upward migration.
Why put plastic under concrete?
One contractor says to put plastic under the concrete, it prevents moisture from coming up into the concrete. The other contractor says NO Way, No plastic, holds the water in the concrete during the drying process and can leave webbing like visual affect in finish of concrete. What is correct?
Why use vapor barrier on concrete?
The main reason for vapor barrieers to be used in concrete applications is for things like a basement floor. For example, a floor that will be tiled over, sub floor glued, etc. The moisture coming up from the concrete can weaken the adhesives and cause loose tiles, etc.#N#The drawback to these vapor barriers again is excessive moisture in the curing process. If the mix retains too much moisture, it can lead to delamination of the concrete. I dont think you want the surface of your floor to blister and peel away. There's a lot of variables here, and in theory the vapor barriers sound good. But, check into it toroughly. Ive been doing concrete and been around concrete for a long time, and Ive never seen anyone put plastic under a garage slab around here.
Does plastic hold water?
If your contractor is good with concrete then he should have no problems with the finish with plastic. It will hold a little more water, but nothing thats major.
Can you put poly on concrete after tamping?
Depends on soil conditions. If the soil is sandy type or similar, after tamping the floor area I would put a layer of poly. If you don`t, it will suck the water from the pour and cause problems. There are times in hot weather where wetting the concrete is needed to slow the curing process.
Does concrete need water?
Too much water in the mix dilutes the concrete, and will reduce the strength, possibly causing cracks, peeling, surface ships etc. I would not worry about moisture coming up from the ground damging the concrete. Once its cured, the moisture wont hurt it. Concrete is used on sea walls, piers, drains, sewers, etc. Most important is to get a good mix, some steel in it, 4" minimum on thickness, good weather for the pour, and a good Finisher.
Why does concrete crack when pouring?
Pouring concrete directly onto dirt can cause the pad to crack or shift out of level as the soil underneath settles. Excess ground moisture can also degrade the concrete causing it to fail or crumble, especially if there is any freeze-thaw action. Heavy loads placed on or moving across the concrete can also cause it to fail or crack. Proper site preparation is important when planning a concrete pour.
Where should moisture barrier be placed for concrete?
When preparing for a concrete pour, the vapor retarding barrier should be placed directly below where the concrete will be poured.
How much permeance does concrete have?
Standard concrete has the permeance of 3.2 Perms IMP which will allow ground moisture to wick up through it. A layer of 6-mil poly has the permeability of 0.059 Perms IMP and 10-mil poly 0.3 Perms IMP. The thicker the poly, the better and more durable the barrier. It is interesting to note, though, that 1 mil aluminum foil has the permeance of 0.00 Perms IMP.
How thick should a moisture barrier be?
A moisture retarding barrier needs to have a permeance of 0.06 Perms or less. It should also be at least 6 one-thousandths of an inch thick to withstand punctures and tears during the concrete pour. The IRC identifies 6-mil polyethylene as the minimum acceptable barrier for under concrete, and the ACI states 10-mil poly as their minimum recommended choice.
What is the minimum vapor barrier required for concrete?
Concrete slabs that will be within heated structures must have a vapor barrier. Subsection R506.2.3 of the 2018 IRC states that a minimum of 6-mil polyethylene vapor retarder be used between the concrete and the base course or prepared ground. It also requires seams or joints in the barrier to have a minimum 6” overlap sealed with compatible material.
What is the best material to use for vapor barrier?
A common practice is to use a thin layer of polyethylene (plastic) sheeting as a vapor barrier. The permeable nature of concrete allows ground moisture to penetrate upward to flooring or anything in contact with the concrete.
Why do you need a vapor barrier on a concrete floor?
A vapor barrier under the concrete decreases the amount of moisture that can wick through the concrete and into the living space.
What is on top of concrete before poured?
Before they poured the concrete slab, they installed a layer of plastic sheet on top of the ground ... and of course you can see the rebar on top of the plastic that will reinforce the cement.
Why is plastic liner good?
A plastic liner is good because it will stop some moisture from coming up through the slab... as long as it's the right kind of plastic.#N#The alkali in concrete will eat away at many plastics and disintegrate them over time.
Is plastic good for concrete?
I would think that the plastic is a good idea since it will keep the damp earth below it from effecting the concrete slab above and maybe keep ground moisture from entering the house later on.
Does concrete cure by drying out?
Concrete does not cure by drying out but through a process call hydration. Installing a barrier such as polyethylene below the slab retards the transfer of moisture from the ground to the concrete. Your friend sounds like he has heard an urban legend or he's pulling your leg.
