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.
Is it OK to 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? Plastic or No plastic????
Can I use polyethylene at the bottom of a concrete slab?
The other potential issue with polyethylene at the bottom of the sandwich below the rigid foam is that the rigid foam can trap water between the poly and rigid foam. This would mean that the concrete slab might not be cured for over a year.
How to avoid cracks in concrete slabs?
There is no way to avoid any cracks. Slab reinforcing should have a minimum top cover of 3/4". But the closer it is to the top the more effective it is at crack control. So I specify that top cover must be no less than 3/4" and no more than 1".
Can you put gravel 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. In this regard, do you need a vapor barrier under a concrete slab?
Do you need a vapor barrier under a concrete slab?
Exterior concrete slabs or those in unheated structures don't require a vapor retarding barrier. However, if the surface will be sealed with an impermeable membrane or product, there should be a vapor barrier under the pad.
What plastic should I use under concrete?
polyethylene (poly)The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil.
What goes underneath a concrete slab?
The base in concrete construction is the layer between the sub-grade (existing soil) and the concrete slab. The base (usually a crushed stone material) acts as a support between the dirt and slab, and ultimately, reduces cracking of the slab.
Is under slab insulation necessary?
Slab insulation is important not only to save on energy bills, but also to improve comfort. Cold concrete slabs are one of the most notorious sources of discomfort in a home. Installing slab insulation around the perimeter of the slab will reduce heat loss and make the slab easier to heat.
Can you pour concrete directly on dirt?
Long story short, yes you can pour concrete over dirt.
Is plastic required under concrete driveway?
Plastic is a moisture barrier generally to stop ingress from beneath the slab. If this is outdoor in an exposed area it probably doesn't matter. I'd probably use plastic if the area is moist with little sun, just to alleviate any algae growth. It's outdoors, north facing, lots of sun.
How do you prepare the ground for a concrete slab?
2:176:18Pouring a concrete slab: Prepare the Ground & Drainage - YouTubeYouTubeStart of suggested clipEnd of suggested clipThe first thing you want to do is bring in a backhoe or a skip loader and scrape off any organicMoreThe first thing you want to do is bring in a backhoe or a skip loader and scrape off any organic material or topsoil from the area where the slab will be poured topsoil.
Can I pour concrete over rock?
Big rocks are not a problem as long as there is uniform concrete coverage and adequate rebar for temperature fluctuations. If the big rocks protrude up above grade and if you have a few in a row, it will weaken the slab. We like things uniform, including the grade, thickness of the concrete, etc.
How much should I fill under a concrete slab?
This ensures that water is taken away from the foundation. The material still needs to be compacted in order to reduce settling that will occur over time. The top 6 to 12 inches of the backfill under the slab should be filled and compacted with well-graded gravel or crushed material.
Should you put Styrofoam under concrete?
Contractors are increasingly called upon to install rigid foam insulation under concrete slabs and on building foundations. Up to one-quarter of a building's energy loss is due to lack of insulation in below-grade areas, including the foundation and under slabs.
What kind of insulation goes under concrete slab?
0:522:56Insulation for Under Concrete Slab - InfraStop® Concrete Pad - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd expansion joints or your typical concrete pour reflective under slab insulation reduces radiantMoreAnd expansion joints or your typical concrete pour reflective under slab insulation reduces radiant heat loss and redirects radiant heat energy back to the living area it saves energy usage and lowers
Why it is unnecessary to insulate under an entire concrete slab on ground?
Installing thermal insulation on below-grade foundation or perimeter walls and under slabs is important because un-insulated concrete provides a thermal and moisture bridge between the heated building interior and the relatively cooler earth surrounding the building, or through exposed slab edges to the outside air.
Do You Need Plastic Under Concrete Driveway?
Concrete is a versatile material that you may use for various purposes, including flooring. Extensive planning is required when preparing to cast a concrete driveway or other construction. A critical choice is whether to install a vapor barrier underneath the concrete driveway or not.
What Are the Characteristics of a Plastic Barrier Used in Construction?
A vapor or plastic barrier is a layer that prevents or slows the entry of moisture vapor. A moisture or vapor retarder is another name for it.
Is Installing a Vapor or Plastic Barrier Under a Concrete Driveway Necessary?
Although concrete may take up to a month to cure entirely, it begins to harden within an hour of pouring and cures entirely within 24 hours, resulting in a firm slab that you can utilize immediately. As a result, whatever you intend to put in or beneath the concrete must be present before pouring.
What Is the Difference in Terms of What Vapor and Moisture Barriers Do?
Vapor or moisture diffusers or retarders are part of a building’s moisture control. A vapor diffuser or retarder helps keep moisture vapor from entering a structure or material. Many commonly call a vapor barrier and a moisture barrier a vapor diffuser or retarder.
What Kind of Vapor Barrier Can I Use Under Concrete?
To be safe, a vapor retarder placed beneath the concrete to prevent moisture movement must have a Class 1 overall score and permeability of 0.06 Perms IMP or lower, according to the code. A Perms IMP score of 0.059, which is roughly 0.06 Perms IMP. Polyethylene was not permitted to be thinner than six mils in 2018.
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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.
Is 5" mesh a good thickness?
5" is plenty of thickness as long as the sub- grade is right and there is mesh.
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.
What goes under a slab of concrete?
Eventually, contractors discovered that it made sense to include a 4-inch-thick layer of crushed stone under the concrete. The crushed stone provides a capillary break that reduces the amount of moisture flowing upward from the damp soil to the permeable concrete.
Why is polyethylene used in concrete?
Concrete contractors learned that a layer of poly helps to keep a slab dry, because it stops upward vapor diffusion from the soil.
Why is crushed stone used in concrete?
Since the crushed stone layer provides a fairly uniform substrate, it also may also reduce the chance that a concrete slab will be poorly supported by random pockets of soft, easily compressible soil .
What are the layers of a building?
According to most building scientists, here’s how the layers should go, from the bottom up: crushed stone; rigid foam; polyethylene; concrete.
Can you put a roof before slab preparation?
the only thing you should matter is to put a roof before doing slab preparation and this solution is also valid with standard foam when you have to fix some pipes on wire mesh, usually the poly end up with a lot of holes in it.
Can you put blotter sand on concrete?
The answer is yes. To understand why, it’s useful to study the history of blotter sand. Beginning in 1989, the American Concrete Institute (ACI) recommended the installation of a 4-inch layer of granular material between a sub-slab vapor retarder and a concrete slab.
Is concrete a good vapour barrier?
Because concrete is an extremely effective vapour barrier, we aren't concerned about vapour from the house condensing on the "cold side" of our insulation against the poly and building up there below the foam (which is why one would normally place poly on the warm side of their insulation a-la walls and roof).
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.
How long does it take for concrete to harden?
Although concrete will take up to a month to fully cure, it begins to harden within an hour of pouring and makes a finished usable solid slab within 24 hours. So, anything you want in or under the concrete needs to be there before the pour. Always check with the local building department or a professional before pouring.
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.
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.
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.
What is a vapor barrier for concrete?
Many moisture problems associated with interior concrete floors and slabs on grade can be minimized or eliminated by installing a vapor barrier under the concrete. A vapor barrier should be used for all concrete floors and slabs that are going to receive an impermeable floor finish like epoxy, laminate, linoleum, ...
What happens when water vapor evaporates from concrete?
Water vapor that passes through the concrete will evaporate if the concrete surface isn't sealed or covered by a material that doesn't allow the concrete to breathe. Floor coverings like linoleum, vinyl tile, wood, carpeting, and epoxies, seal the moisture in the concrete where it eventually causes the floor covering to loosen, blister, or buckle.
