What is a vapor barrier over concrete?
Concrete Vapor Barrier. A concrete vapor barrier is simply a sheet of polyethylene plastic (Visqueen) placed directly on top of the sub-grade before the concrete floor or slab is poured to help keep moisture from the soil from passing up through the concrete. Many moisture problems associated with interior concrete floors and slabs on grade can ...
Do I need moisture barrier on a concrete slab?
One important decision is whether or not to use a vapor barrier under concrete slab construction. Concrete is permeable, so ground moisture can penetrate upward to the surface. If the pad surface is sealed with an impermeable finish or protected and heated by a permanent structure, it should have a vapor barrier.
Can I use hardibacker over concrete slab?
Yes, you can use this concrete on other surfaces as well. Starting from ceramic tile, wood, LVP, and plywood, you can use the compound on any surface. Hence, you can also use it over a hardibacker and any non-flexible surface. 4. Easy User Interface & No Allergic Reaction. The compound is straightforward to use.
How to install poly vapor barrier?
How to Use Plastic As a Vapor Barrier in the Walls
- Considerations. The standard installation of a plastic vapor barrier is between the studs and the drywall, but there are some exceptions to this.
- Exterior Walls. Warm air inside the home will produce condensation inside the exterior walls wherever it comes into contact with the colder outside air.
- Interior Walls. ...
- Standard Installation Practices. ...
How thick should a vapor barrier be under a concrete slab?
10 milsThe American Concrete Institute's Guide for Concrete Floor and Slab Construction recommends that the thickness of the vapor retarder be at least 10 mils.
Where do you put vapor barrier under a slab?
Most exterior slabs do not need a vapor barrier. ... In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. ... The vapor barrier can be placed under the subbase, if the building is closed in when the dry subbase material is placed.More items...
What plastic do you use under a concrete slab?
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 is the purpose of plastic sheeting under a concrete slab?
The sand layer cannot dry downwards by vapor diffusion because of the plastic sheet—it is a vapor barrier after all. In fact that's why we have it under the slab. We want a vapor barrier under the slab. ** We want to prevent water vapor from coming up from the ground into the concrete slab.
Do you need rebar for 4 inch slab?
For 4” concrete slabs used for driveways and patios, #3 rebar is common. Driveways that will support daily traffic by heavy trucks frequently use 1/2″ or #4 steel bar.
What is the best vapor barrier for a concrete floor?
Polyguard – The Best Prevention Against Water and Vapor Transmission Through Concrete Slabs on Grade. Polyguard Underseal Underslab Membrane and Polyguard TERM Floor Underlayment Barrier.
Is it a good idea to put plastic under concrete?
0:101:02Why a Plastic Vapor Barrier Under Concrete Slab - Mondays with MikeYouTubeStart of suggested clipEnd of suggested clipProducts really on the ground whether it be tile wood vinyl all those things are going to have aMoreProducts really on the ground whether it be tile wood vinyl all those things are going to have a problem if you don't put down a plastic vapor barrier. That's what this is.
Do you need plastic under slab?
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.
Can you pour concrete directly on dirt?
Long story short, yes you can pour concrete over dirt.
What happens if you don't have a vapor barrier?
The short answer is: if your wall doesn't have a vapor retarder, there is no need to worry. Builders worry way too much about vapor diffusion and vapor retarders. It's actually very rare for a building to have a problem caused by vapor diffusion.
Is gravel needed under concrete?
You do need gravel under a concrete slab, footing, or patio. Gravel provides a solid foundation for your concrete as it can be compacted. It also improves drainage, preventing water from pooling beneath the concrete.
Should I put a membrane under concrete?
The concrete, or slab base, should contain a damp-proof membrane (sized to the entire surface area the shed will occupy). This should be inserted below the flags, or 2” below the surface of the concrete slab.
Does vapor barrier go above or below slab insulation?
Notice that the sheet polyethylene “vapor barrier” is located on the top of the rigid insulation between the rigid insulation and the bottom surface of the concrete – in direct contact with the concrete. Do not, and I repeat, do not locate the polyethylene under the insulation as it will keep the insulation wet.
How do you put plastic under a concrete slab?
0:101:02Why a Plastic Vapor Barrier Under Concrete Slab - Mondays with MikeYouTubeStart of suggested clipEnd of suggested clipBut you want to have a six mil plastic. That's code to put down over the slab or I should say theMoreBut you want to have a six mil plastic. That's code to put down over the slab or I should say the dirt. Before you pour your slab. The reason that is is moisture migrates from the dirt up.
How do you install a vapor barrier on a concrete floor?
How to Install a Vapor Barrier on a Concrete FloorSelect the Vapor Barrier. ... Clean Floor and Perimeter Walls. ... Apply Butyl Tape to Walls. ... Unroll and Trim Vapor Barrier Sheets. ... Apply Vapor Barrier Seam Tape. ... Fasten Vapor Barrier to Wall.
How do you install a vapor barrier before pouring concrete?
0:101:15Installing vapor barrier before pouring concrete slab - YouTubeYouTubeStart of suggested clipEnd of suggested clipWe actually tape. So that the pipes can come up in the concrete can surround them. So they don'tMoreWe actually tape. So that the pipes can come up in the concrete can surround them. So they don't just lean back with the plastic on top we actually break these through the vapor barrier.
What is vapor barrier?
First, a vapor barrier provides a consistent, smooth surface for concrete placement teams. This can be a time-saver where the placement team has a predictable surface on the site throughout.
What happens if you don't have a vapor barrier?
Without a vapor barrier, moisture would continually wet the bottom of the slab, as vapor will continuously drive from the high humidity below slab to the relatively low humidity above the slab. Without a vapor barrier in place, a slab that dries from its top surface will be exposed to disproportionate moisture levels in the slab for its entire lifetime. This is a far greater curling threat to the foundation, long-term.
How can a vapor barrier help with radon?
Moisture, however, may be the least of the problems passing through the concrete foundation that can negatively affect the air quality inside your building. Radon, for example, is the second leading cause of lung cancer in the United States, and the leading cause among non-smokers. A below-slab vapor barrier can also help prevent sub-slab radon ingress. Many vapor barriers are synonymous with soil-gas retarders in construction language. When evaluating the performance qualities of vapor barriers as soil-gas retarders, be sure to check the radon diffusion coefficient of the material before you select it. While there are many factors to consider, a general rule of thumb is: the lower the radon diffusion coefficient, the better.
What happens if water vapor is poured through concrete?
Water vapor diffusing through the concrete slab can also lead to deformation and discoloration of the floor covering material, leading to costly repairs or even replacement. The cost of a vapor barrier – installed on the foundation before concrete placement – is far more economical than these nightmare scenarios. 2.
Why do green buildings have vapor barriers?
That’s one reason why most green building codes and best practices include a high-performance vapor barrier in their specifications. A more energy-efficient building is better for the environment and your bottom line. 6. Your floor covering warranty may require it. Always read the fine print.
Why use a high performance vapor barrier?
Floor failures are not. The single most important reason you should use a high-performance vapor barrier is to protect the expensive floor covering in your building.
Can moisture be vapor barriers?
Here’s the problem with that logic: the moment you start putting materials down on the exposed concrete, those items become vapor barriers. Moisture will have a harder time moving through product inventory and its packaging and will instead begin condensing and pool ing on the floor below, in the right (or wrong) conditions. That accumulation of water can destroy sensitive products. Chances are – replacing them will be much more expensive than installing that high-performance vapor barrier in the first place.
What are Vapor Barriers?
All of the problems associated with moisture vapor movement in a concrete slab will go away in time as the slab dries, as long as there is no source of additional water into the slab. Since the most common source is moisture in the ground beneath the slab, the solution is to completely take the ground out of the equation, by sealing the bottom of the slab.
What is the minimum thickness of a vapor barrier?
ACI 302.1, Guide for Concrete Floor and Slab Construction, states that the minimum thickness of an effective vapor barrier is 10 mils. This was verfied by some field studies conducted by Concrete Construction magazine. Thinner plastic can't stand up to the abuse of construction. ASTM E-1745 specifies minimum values for tensile strength and puncture resistance that increase from Class C to Class A.
Why is 6 mil visqueen used under concrete?
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. 6-mil plastic often gets damaged during placement of reinforcement and concrete, ...
How much perms does a vapor retarder have?
For all three classes of vapor retarder, the permeance (a measure of how much vapor can pass through) must be less than 0.3 perms. Most experts today don't think that's low enough, and a few materials have recently become available that have permeance values less than 0.03 perms—some as low as 0.01.
How much does a 15 mil vapor barrier cost?
Typical 8-mil polyethylene sheeting costs 5 to 7 cents per square foot. A 15-mil vapor barrier can be about 25 cents per square foot. Sure, that's an increase, but it's better than a damp, discolored slab.
How to make sure slab is dry?
Bottom line: If you want to make sure your slab on ground gets dry and stays dry, use a vapor barrier.
Why are basement floors like concrete?
One of the reasons those old basement floors were like that was because they had no vapor barrier beneath them, leaving an easy path for water vapor from the soil to migrate into the slab, ...
What can I use for a vapor barrier under concrete?
Most vapor barriers are created using polyethylene or polyolefin sheets that are strong enough ( at least 10 mils thick) to tolerate the kind of heavy construction activity that goes on over concrete subfloors.
Why is a vapor barrier needed under concrete?
This is why a vapor barrier under concrete is essential. Vapor barriers are a way to keep moisture from getting into the concrete. Note: A vapor barrier is not the same as an underlayment. However, there are underlayments that act as vapor barriers. Vapor barrier permeability is expressed in perms.
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.
Why is too much moisture in concrete a problem?
One word: adhesives. Too much moisture in concrete is a problem because it can cause pH changes that destroy adhesives. Here’s what happens.
Where should a vapor barrier be installed?
What type of moisture barrier should be used and where it should be installed is a subject of debate. Some think vapor barriers can cause slabs to curl and that simply pouring concrete directly onto a granular base (gravel, crushed rock, etc.) should be enough. Others see vapor barriers as essential and argue that they prevent adhesive failures, retard the growth of mold and mildew, and even prevent certain noxious gasses from entering a building.
How thick should a vapor retarder be?
According to the Guide to Concrete Floor and Slab Constructionpublished by the American Concrete Institute, a vapor retarder should not be less than 10 mils thick. (A mil is one-thousandth of an inch.) You might need an even thicker barrier though if you’re covering material with sharp angles.
Why do we use vapor barriers?
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 dryto avoid flooring problems. If you’ve ever had a problem with a basement floor (or any concrete floor), you know the kind of damage that too much moisture can cause.
Where should the under slab vapor barrier be located?
From a moisture-protection standpoint, it is my strong belief – reinforced by decades of ACI study and expert opinions – that the under-slab vapor barrier should be located directly below the slab, without the use of a layer of granular fill (sometimes sand) sandwiched between the slab and vapor barrier, often referred to as a “blotter layer.”
What is the permeance rating of below slab vapor barrier?
A below-slab vapor barrier has a permeance rating of less than 0.01 perms to provide exceptional protection against water vapor diffusion. Making sure that vapor barrier meets ASTM E1745 Class A is important as well. To meet Class A specifications, it must also have a minimum tensile strength of 45 lbs/in. and a minimum impact puncture resistance of 2,200 grams, which both demonstrate the membrane’s ability to withstand the construction environment.
Why do we need blotter layers?
Proponents of blotter layers point to its ability to allow bleed water to leave the bottom of the slab, thereby helping to maintain an expected finishing schedule.
Can a blotter layer dry more evenly?
Many designers and contractors may believe that a blotter layer can allow the slab to dry more evenly. This is often true, at least initially, but the potential benefit is often outweighed by the associated costs. Each of the four factors I’ve provided below—intended to help project teams select the location of their under-slab vapor barrier—will also explain the many unintended consequences of a blotter layer that their users may not have considered.
Can moisture sensitive floor coverings be stored in contact with slabs?
Another consideration: even if there’s no possibility for a moisture-sensitive floor covering, will there be moisture-sensitive goods stored in contact with the slab? If so, your answer here is also ‘yes,’ as these goods can be degraded or spoiled by moisture vapor diffusing through the slab – accumulating and condensing on their undersides – as well.
Why do concrete slabs need vapor barriers?
But they have also proven to be beneficial in reducing failures of moisture-sensitive flooring materials, adhesives, and coatings caused by excessive emission of moisture vapor from concrete slabs.
How long does it take for moisture to evaporate from a concrete slab?
The rate that moisture escapes from a slab depends on the concrete w/c, the density of the finish, the ambient conditions above the slab, and the moisture below the slab. One laboratory drying study indicated that 4-in. thick concrete samples, having a w/c=0.50 and sealed from below, required 82 days for the vapor emission rate to reach 3.0 pounds per 1000 square feet per 24 hours. The ambient air above the sample was 73°F and 50% relative humidity. The same concrete not sealed from below required 144 days to reach the same vapor emission rate. Concrete having a w/c=0.40 and sealed from below required 46 days to reach the 3 pound per 1000 square feet per 24 hour vapor emission rate, while the same concrete not sealed from below required 52 days to achieve this rate. This study reinforces the benefit of using concrete having a w/c less than 0.50, and the need to reduce the slab moisture entering from below when moisture-sensitive flooring materials will be installed.
How much fill should I put on a vapor retarder?
Until 2001, the American Concrete Institute (ACI) recommended 4″ of granular fill be placed atop vapor retarders.
Where to put vapor retarder?
Place the vapor retarder on top of the granular material and directly beneath the slab for moisture-sensitive floor covering and coating applications. However, in doing so, recognize that additional attention should be given to the design of reinforcement so that potential curling stresses within the slab are addressed.
How much does it cost to cover concrete floors?
However, the fact that the cost of floor coverings over concrete floor slabs in the U.S. is now estimated at over one billion dollars a year requires that greater attention be given to concerns about moisture within and below these slabs.
Is a low W/C concrete good for a slab?
However, using a concrete with a low w/c alone is often insufficient to satisfy the floor covering industry’s moisture emission requirements. Even after what appears to be sufficient drying of the surface, moisture will redistribute itself once the floor is covered. Without sufficient subslab moisture protection the total moisture in the slab will increase over time, and sawed contraction joints and random cracks will provide passageways for moisture to migrate through the slab. Omitting a vapor retarder may also result in liability for a flooring failure, since its use is often published in guidelines from many flooring manufacturers.
Does a capillary break prevent moisture from reaching the slab?
However, recognize that the capillary break will not prevent moisture from reaching the slab in vapor form.
How long does it take for a slab to dry out?
Slabs that lack under-slab vapor barriers will nearly always have some water vapor emission from water below the slab, and newer slabs, even with vapor barriers, will need time to dry out. Overlay manufacturers typically recommend a moisture vapor emissions rate (MVER) of 3 pounds per 1000 square feet in 24 hours ...
What is the initial preparation of a floor?
The initial preparation of the floor is a critical part of the process. "Some floors are so ugly we have to go in first and chase the cracks and fill them with liquid epoxy," he said. "I keep filling the cracks until I get them full before I put the vapor block on.
Where should vapor barrier be in a slab?
For an under-slab vapor barrier to be most effective, it should be in direct contact with the underside of the slab. (Illustration: courtesy IBACOS)
How thick is a sub slab vapor barrier?
The most obvious best practice is to install a sub-slab vapor barrier in the first place. I recommend a minimum 10-mil-thick polyethy lene material, even if your local building code allows a 6-mil, as it lasts longer and is less prone to punctures.
What is the purpose of a polyethylene vapor barrier between concrete and soil?
A properly selected and installed polyethylene vapor barrier between the slab and the soil effectively keeps ground moisture away from the concrete to mitigate these issues. Anything less (or nothing at all) is a recipe for myriad problems down the road.
What is the best way to prevent concrete from curling?
It will prevent edge curl by slowing the curing rate of the slab enough that all the moisture has time to evaporate through the upper surface.
Why do you put sand between poly and concrete?
Some contractors put a layer of sand between the poly and the concrete to give the slab a chance to dry in both directions; however, moisture inevitably gets trapped in the sand, and once the concrete dries, that moisture will begin transferring hygroscopically to the slab.
How to mitigate soil gas intrusion?
To further mitigate soil gas intrusion, install the vapor barrier over a 4-inch bed of level, compacted gravel before you pour the slab. If you also install a vent stack for soil gas, the gravel will provide a base layer through which air can move laterally toward the stack. In areas where soil gas isn’t a problem, the gravel will still serve as a capillary break to keep moisture at bay.
Can you put vinyl flooring on concrete?
Some builders in desert climates ignore this advice, figuring that they don’t have to worry about under-slab moisture. But whether moisture will be a problem depends in part on the finished floor coverings. For instance, if you apply vinyl flooring directly to the slab, even occasional moisture in markets such as Phoenix can be enough to accelerate the potential for failure between the vinyl and the concrete.
Do air barriers need to be continuous?
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. It’s that Fick’s Law thing.
Does polyethylene need to be protected?
Joe Lstiburek explains it well in this article: https://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems. "The polyethylene does not need protecting.
Do you need to seal polyethylene before placing concrete?
The polyethylene is a vapor barrier, not an air barrier, so there is no need to seal the poly to the foundation wall before placing the concrete. Always place the polyethylene barrier above the insulation. Otherwise you will trap water in the insulation layer, which is bad.
Is polyethylene a vapor barrier?
The damage to the polyethylene is minimal- it's still a vapor barrier even if not air tight. Putting the polyethylene above the foam minimizes the risk of "iceberging", where if concrete gets under a corner of the foam during the pour it floats up, creating a thin spot in the concrete or even sticking out of the top surface.
Causes
Safety
Treatment
Prevention
- The preventative measure most often used to try to circumvent these contact moisture-related challenges is to install a vapor barrier. But what type and where it should be installed has been a subject of much debate. Some feel that vapor barriers contribute to curling in the slab and that simply casting on a granular slab should be sufficient. Others feel a vapor barrier is a critical ele…
Introduction
- Technically, any material that resists moisture passage is a vapor barrier, a term often used interchangeably with a vapor retarder. But very few are true barriers as they still have a low level of permeance, or the ability to let water vapor pass through. This is often expressed as perms that allow for categories of permeability. The degree of permeability that is acceptable may depend …
Use
- Currently, a vapor barrier is typically applied over a layer of granular fill to try to minimize the wicking effect of ground moisture. Of course, if the vapor retarder is penetrated, it will not be effective in preventing moisture migration. Seams must be properly sealed, heavy grade materials must be used where traffic may cause penetration, and the lowest possible grade of permeance …
Mechanism
- It must be noted that this practice, though, causes slower drying times because moisture cannot leave a drying slab through an impermeable sub-layer. With the vapor barrier directly under the slab, moisture then has to move to the surface of the slab and evaporate from there. Placing the vapor barrier under the granular layer let contractors float the concrete sooner and appeared to …
Risks
- Because there are pros and cons to both situations, accurate relative humidity testing is also necessary to be sure slab moisture conditions are ready for the flooring or finish application of choice. Moisture-sensitive adhesives and applications can be just as adversely affected by a moisture level too high in the slab as they can by moisture-wicking problems due to an inadequa…
Preparation
- There is only one chance to make the best vapor barrier choice, and obviously, that is before the slab is poured. For each concrete slab, it is imperative to understand the best vapor barrier choice based on local conditions, recommended guidelines and careful application. With the correct vapor barrier under the slab, and a knowledge of slab moist...