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Just what is a concrete vapor barrier?

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

If you’ve had a problem with a basement floor (or any concrete floor), you realize the type of damage that as well much moisture may cause. Moisture enters concrete in a number of ways, including via the ground, from humidity up, and throughout leaky plumbing that passes through a slab. Naturally, there’s also the moisture which was inside the original concrete mixture.

There’s only one-way moisture leaves concrete, though, and that’s via its surface. For those who have a concrete floor that’s in continuous exposure to an origin of moisture, you’re going to have problems. For this reason a vapor barrier under concrete is vital. Vapor barriers are a great way to hold moisture from getting yourself into the concrete.

Note: A vapor barrier isn’t the comparable to an underlayment. However, you will find underlayments that behave as vapor barriers.

Vapor barrier permeability is expressed in perms.

Vapor barriers have varying levels of permeability, expressed in perms. The better the number, the greater permeable the fabric. Impermeable vapor barriers are those with a rating of 0.1 perm or less while class II vapor retarders are the ones using a rating higher than 0.1 perm and less than 1.0 perm.

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

Why is excessive moisture in concrete an issue?

One word: adhesives. A lot of moisture in concrete is a problem as it can cause pH changes that destroy adhesives. Here’s what are the results.

As moisture makes its strategy to the outer lining of a concrete slab, soluble alkalies come along for that ride and lift its surface pH above those of flooring adhesives. This will cause the adhesives to breakdown and you also end up with flooring failures for example swelling, bulging, or cupping.

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

In short, yes. Here’s why.

There’s almost always water underneath a structure site. It might not be close to the surface, however that doesn’t mean it’s not there. This water can progress up with the soil and are avalable into connection with the foot of a concrete floor via capillary action. Capillary action can be stopped by installing something known as a capillary break, a layer of crushed rock which goes involving the subgrade as well as the slab.

Capillary breaks do an adequate job of stopping water in its 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 under the slab that prevents vapor moisture from entering.

You have to 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 accordance with the Guide to Concrete Floor and Slab Construction published by the American Concrete Institute, a vapor retarder mustn’t be below 10 mils thick. You will need a good thicker barrier though if you’re covering material with sharp angles.

Important thing: Vapor barriers have to be sufficiently strong enough enough in order that they don’t easily puncture. If they do, moisture will get in and that’s what you’re always keeping out.

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