Exactly what is a concrete vapor barrier?

A concrete vapor barrier is any material that stops moisture from entering a concrete slab. Vapor barriers are used because while fresh concrete flows wet, it’s not supposed to stay this way. It has to dry after which stay dry to prevent flooring problems.

If you’ve ever had an issue with a basement floor (or any concrete floor), you know the level of damage the exact same thing much moisture may cause. Moisture enters concrete in a variety of ways, including through ground, from humidity via a flight, and thru leaky plumbing that goes through a slab. Needless to say, there’s even the moisture that 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 exposure to a source of moisture, you’re likely to have issues. This is why a vapor barrier under concrete is essential. Vapor barriers are a good way to keep moisture from engaging in the concrete.

Note: A vapor barrier is not the comparable to an underlayment. However, you can find underlayments that become vapor barriers.

Vapor barrier permeability is expressed in perms.

Vapor barriers have varying examples of permeability, expressed in perms. The higher the number, the greater permeable the material. Impermeable vapor barriers are the ones using a rating of 0.1 perm or less while class II vapor retarders are the types using a rating more 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, as it happens, they aren’t exactly the same thing. Vapor barriers are less permeable than vapor retarders. On this page, we are with all the term ‘vapor barrier’.

Exactly why is a lot of moisture in concrete a difficulty?

A word: adhesives. A lot of moisture in concrete is a concern because it may cause pH changes that destroy adhesives. Here’s what goes on.

As moisture makes its method to the outer lining of an concrete slab, soluble alkalies arrive for your ride and raise its surface pH above those of flooring adhesives. This will cause the adhesives to breakdown and you also end up getting flooring failures like swelling, bulging, or cupping.

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

In short, yes. Here’s why.

There’s typically water underneath a building site. It may not be near the surface, but that doesn’t mean it’s not there. This water can move up through the soil and are avalable into experience of the bottom of a concrete floor via capillary action. Capillary action can be stopped by using something known as a capillary break, a layer of crushed rock which goes between your subgrade along with the slab.

Capillary breaks do an adequate 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 layer of concrete. Therefore, there must be something under the slab that forestalls vapor moisture from entering.

You might also need a vapor barrier for liability reasons since the majority manufacturers of flooring include vapor barriers or retarders inside their installation guidelines.

How thick should a plastic vapor barrier be?

In line with the Guide to Concrete Floor and Slab Construction created by the American Concrete Institute, a vapor retarder should not be less than 10 mils thick. You need a level thicker barrier though if you’re covering material with sharp angles.

Main point here: Vapor barriers have to be sufficiently strong so they don’t easily puncture. Whenever they do, moisture are certain to get in and that’s what you’re always keeping out.

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