Ethan Clarke
Whether or not to use plastic under a concrete driveway is a question that has been asked for many years, with some arguing that it is unnecessary and even detrimental. Concrete is a porous material that requires extensive planning when preparing to cast a driveway. One of the critical choices is whether to install a vapor barrier, which prevents or slows the entry of moisture. While some argue that plastic under an outdoor concrete slab is unnecessary and may even prolong the time needed to get rid of bleed water, others claim that it helps create a nice, strong pour. Additionally, concrete is mostly water, and without plastic, the water can leach away, causing the concrete to cure incorrectly. To comply with ASTM standards and protect the building project and its occupants, vapor barrier plastic is required under concrete slabs.
Do you need plastic under a concrete driveway?
| Characteristics | Values |
|---|---|
| Purpose | Prevent water loss during curing, protect against decay and cracking, and act as a vapour barrier to protect against environmental damage |
| Requirements | Minimum 6-mil polyethylene vapour retarder, 6-inch overlay of seams or joints, suitable sealing material, thicker poly for better barrier and puncture resistance |
| Recommendations | Use impermeable layer or substance, choose least breathable and most durable material, follow ASTM E1643 guidelines for installation |
| Benefits | Strong concrete pour, protection from moisture, pests, and extreme temperatures, added insulation against heat and cold |
| Considerations | Potential for slip hazard during installation, potential for prolonging time needed to get rid of bleed water, potential for surface de-lamination |
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What You'll Learn
Concrete is porous and needs protection
Concrete is a porous material that requires protection from environmental factors. When preparing to cast a concrete driveway, it is essential to decide whether to install a vapour barrier underneath it. Concrete floors exposed to the outdoors need protection to prevent rainwater from permeating the surface.
A vapour barrier is a layer that prevents or slows the entry of moisture vapour. This protective layer is placed underneath the concrete foundation before it is poured to prevent water vapour from penetrating the concrete subfloor and damaging the main floor of buildings. Failure to install a vapour barrier can lead to flooring damage, including bumps, ridges, or bubbles under the flooring, colour changes due to fading, and mould or mildew growth.
Additionally, concrete needs water to cure correctly. Without a vapour barrier, water can leach away from the concrete, resulting in improper curing and a weakened structure. The vapour barrier also helps protect the building's foundation from environmental damage caused by moisture, pests, and extreme temperatures.
The American Concrete Institute (ACI) recommends using at least 10-mil polyethylene or thicker for vapour retarders under concrete. Thicker poly creates a better barrier and is more puncture-resistant. For smaller residential projects, a product like Pro Crawl Barrier or reinforced plastic sheeting can be effective. It is important to follow ASTM E1643 guidelines when installing a vapour barrier, including overlapping seams and sealing them properly.
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Plastic helps with curing and prevents water loss
Concrete is a porous material that can be used for various purposes, including flooring. When preparing to cast a concrete driveway, it is critical to decide whether to install a vapor barrier underneath. This is because rainwater from the ground can permeate the surface of the concrete. Concrete floors exposed to the outdoors should be sealed to prevent water damage.
A vapor barrier is a layer that prevents or slows the entry of moisture vapor. Vapor retarders under concrete should be at least 10-mil polyethylene or thicker, according to the American Concrete Institute (ACI). Thicker poly creates a better barrier and is more puncture-resistant. Concrete curing covers with polyethylene properties are water-resistant and can resist punctures and tears, making them ideal for concrete curing. They can retain the ideal temperature, allowing concrete to achieve its required strength for durability.
The curing process is a gradual process that prevents cracking. Plastic is placed over the concrete to trap water inside, ensuring gradual curing. The covers can heat up to 110°F and trap moisture and heat, which helps accelerate the curing process. Concrete curing covers are lightweight and provide an effective method for temporary insulation.
In addition to curing concrete, concrete curing covers can also be used for ground and scaffolding covers. They can also be used as insulation at construction sites and reduce heating costs. Concrete is mostly water, and it needs water to cure. If no plastic is used, the water leaches away, and the concrete does not cure correctly.
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Vapor barriers are required for heated structures
Concrete is a porous material that requires extensive planning when preparing to cast a driveway or other construction. One critical choice is whether to install a vapor barrier underneath.
The International Building Code defines a vapor retarder as 1.0 perm or less. Vapor barriers can also double as added insulation, protecting buildings from excess cold and heat. In heating-dominated climates, an interior vapor retarder is useful, while in cooling-dominated climates, an exterior vapor retarder is recommended. Vapor retarders are placed towards the interior, heated side of insulation in the assembly in most parts of North America.
The American Concrete Institute (ACI) recommends that vapor retarders under concrete should be at least 10-mil polyethylene or thicker. The IRC also specifies that a minimum of 6-mil polyethylene vapor retarder must be installed between the concrete and prepped ground for all concrete slabs used in heated structures.
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Plastic can slow the dissipation of bleed water
Concrete is porous, and rainwater from the ground can permeate the surface. Concrete floors exposed to the outdoors should be sealed or protected in some way. One way to do this is to install a vapour barrier, which prevents or slows the entry of moisture vapour.
A vapour barrier is a layer of plastic that goes underneath the concrete. The American Concrete Institute (ACI) recommends that the vapour retarders under concrete should be at least 10-mil polyethylene or thicker. Thicker poly creates a better barrier and is more puncture-resistant.
However, some sources argue that plastic under an outside slab might be a bad idea in certain parts of the world. In areas subject to freeze-thaw cycles, air-entrained concrete should be used. Plastic could prolong the time needed to get rid of bleed water. If the concrete is finished before the bleed water has dissipated, surface de-lamination can occur.
On the other hand, some people argue that plastic helps to get a nice, strong pour, and it is cheap and easy to do. Without plastic, water can leach away, and the concrete will not cure correctly.
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Vapor barriers protect against radon gas
Concrete is a versatile material used for various purposes, including flooring and driveways. When preparing to cast a concrete driveway, one critical choice is whether to install a vapor barrier underneath. A vapor barrier is a layer that prevents or slows the entry of moisture vapor. While vapor barriers are not necessary for all concrete installations, they are essential for certain applications, such as concrete slabs in heated structures.
Vapor barriers are crucial in protecting buildings and their occupants from the harmful effects of radon gas. Radon is a colorless, odorless, and radioactive gas that can enter buildings through small cracks or holes in concrete slabs, posing serious health risks, including lung cancer. Installing a radon vapor barrier with a radon mitigation system helps prevent radon accumulation and protects the building's foundation.
The effectiveness of a vapor barrier in mitigating radon depends on several factors, including its radon diffusion coefficient, durability during installation, and longevity beneath the slab. The American Association of Radon Scientists and Technologists (AARST) and the Environmental Protection Agency (EPA) recommend using a soil-gas retarder, typically a minimum of 6-mil thick polyethylene sheeting, beneath concrete floor slabs. Thicker poly creates a better barrier and is more puncture-resistant.
To ensure the vapor barrier effectively mitigates radon, it must be completely sealed around the foundation and support columns. Additionally, a radon fan drawing air from under the barrier can enhance its effectiveness. While a vapor barrier is a crucial component of radon mitigation, it may not be sufficient on its own for high radon levels. In such cases, additional measures, such as improving crawl space ventilation or installing a ventilation fan, may be necessary.
In summary, vapor barriers play a vital role in protecting against radon gas by slowing down its diffusion and preventing its accumulation in buildings. When combined with other radon mitigation strategies, vapor barriers help create a healthier and safer environment for homeowners.
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Frequently asked questions
No, you don't need to put plastic under an outdoor concrete driveway. In fact, doing so might be a bad idea in areas that experience freezing temperatures. However, if your driveway is enclosed within a heated structure, you should install a vapor barrier.
A vapor barrier is a layer that prevents or slows the entry of moisture vapor.
A vapor barrier protects your driveway from decay and cracking. It also protects the main floor of your building from damage caused by water vapor penetrating the concrete subfloor.
The American Concrete Institute (ACI) recommends using at least 10-mil polyethylene or thicker. Thicker poly creates a better barrier and is more puncture-resistant.
