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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 employed because while fresh concrete flows wet, it’s not supposed to stay this way. It must dry after which stay dry to prevent flooring problems.

If you’ve ever had a problem with a basement floor (or any concrete floor), you know the type of damage this too much moisture may cause. Moisture enters concrete in a number of ways, including through ground, from humidity in mid-air, and throughout leaky plumbing that passes through a slab. Obviously, there’s even the moisture that was inside 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 resource of moisture, you’re going to have issues. This is why a vapor barrier under concrete is crucial. Vapor barriers are a great way to hold moisture from getting into the concrete.

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

Vapor barrier permeability is expressed in perms.

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

You’ll hear people using the terms ‘vapor barrier’ and ‘vapor retarder’ interchangeably. However, in fact, they aren’t a similar thing. Vapor barriers are less permeable than vapor retarders. In the following paragraphs, we’ll be with all the term ‘vapor barrier’.

How come excessive moisture in concrete a challenge?

A word: adhesives. A lot of moisture in concrete is a dilemma since it may cause pH changes that destroy adhesives. Here’s what are the results.

As moisture makes its method to the top of an concrete slab, soluble alkalies show up for your ride and lift its surface pH above that of flooring adhesives. This makes the adhesives to breakdown and you also end up having flooring failures like swelling, bulging, or cupping.

Do you need a vapor barrier under a concrete slab?

In a word, yes. Here’s why.

There’s almost always water underneath a building site. It might not be close to the surface, however that doesn’t mean it’s not there. This water can move up over the soil and come into connection with the bottom of a concrete floor via capillary action. Capillary action can be stopped by installing something called a capillary break, a layer of crushed rock which goes relating to the subgrade along with the slab.

Capillary breaks do a passable 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 underneath the slab that stops vapor moisture from entering.

You have to a vapor barrier for liability reasons since the majority of manufacturers of flooring include vapor barriers or retarders in their installation guidelines.

How thick should a plastic vapor barrier be?

In line with the Self-help guide to Concrete Floor and Slab Construction authored by the American Concrete Institute, a vapor retarder really should not be below 10 mils thick. You need an even thicker barrier though if you’re covering material with sharp angles.

Net profit: Vapor barriers should be sufficiently strong so they don’t easily puncture. Whenever they do, moisture are certain to get in and that’s what you’re attempting to keep out.

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