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Exactly what is a concrete vapor barrier?

A concrete vapor barrier is any material that forestalls moisture from entering a layer of concrete. Vapor barriers are utilized because while fresh concrete is poured wet, it’s not meant to stay that way. It has to dry after which stay dry in order to avoid flooring problems.

If you’ve been able to an issue with a basement floor (or any concrete floor), you realize the level of damage this too much moisture may cause. Moisture enters concrete in several ways, including through the ground, from humidity in the air, and throughout leaky plumbing that passes through a slab. Needless to say, there’s the moisture which was within the original concrete mixture.

There’s only one-way moisture leaves concrete, though, and that’s via its surface. In case you have a concrete floor that’s in continuous contact with a resource of moisture, you’re gonna have problems. For this reason a vapor barrier under concrete is vital. Vapor barriers are a way to keep moisture from getting yourself into the concrete.

Note: A vapor barrier isn’t the same as an underlayment. However, there are underlayments that act as vapor barriers.

Vapor barrier permeability is expressed in perms.

Vapor barriers have varying examples of permeability, expressed in perms. The larger the number, the harder permeable the pad. Impermeable vapor barriers are the types with a rating of 0.1 perm or fewer while class II vapor retarders are those using a rating higher than 0.1 perm and much less than 1.0 perm.

You’ll hear people while using terms ‘vapor barrier’ and ‘vapor retarder’ interchangeably. However, in fact, they aren’t exactly the same thing. Vapor barriers are less permeable than vapor retarders. In this article, we are while using the term ‘vapor barrier’.

Why’s an excessive amount of moisture in concrete an issue?

A word: adhesives. Excessive moisture in concrete is a concern given it could cause pH changes that destroy adhesives. Here’s what happens.

As moisture makes its way to the counter of the concrete slab, soluble alkalies show up to the ride and lift its surface pH above those of flooring adhesives. This leads to the adhesives to breakdown and you also end up having flooring failures for example swelling, bulging, or cupping.

Do you want a vapor barrier under a layer of concrete?

In short, yes. Here’s why.

There’s usually water underneath a building site. It might not be at the surface, but that doesn’t mean it’s not there. This water can go up with the soil are available into connection with the bottom of a concrete floor via capillary action. Capillary action could be stopped by using something called a capillary break, a layer of crushed rock which goes between your subgrade and also the slab.

Capillary breaks do a good job of stopping water in their liquid state from reaching a slab. However, they can’t stop water in vapor form from reaching and entering a concrete slab. Therefore, there must be something within the slab that forestalls vapor moisture from entering.

There is also a vapor barrier for liability reasons since the majority manufacturers of flooring include vapor barriers or retarders within their installation guidelines.

How thick should a plastic vapor barrier be?

In line with the Help guide Concrete Floor and Slab Construction provided by the American Concrete Institute, a vapor retarder shouldn’t be lower than 10 mils thick. You may want a much thicker barrier though if you’re covering material with sharp angles.

Main point here: Vapor barriers have to be sufficiently strong enough enough in order that they don’t easily puncture. Whenever they do, moisture will get in and that’s what you’re attempting to keep out.

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