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 utilized because while fresh concrete is poured wet, it’s not supposed to stay this way. It needs to dry and then stay dry in order to avoid flooring problems.

If you’ve ever endured a problem with a basement floor (or any concrete floor), you realize the kind of damage the exact same thing much moisture might cause. Moisture enters concrete in several ways, including through the ground, from humidity up, and throughout leaky plumbing that passes through a slab. Naturally, there’s and also the moisture which was from 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 contact with a source of moisture, you’re gonna have problems. That is why a vapor barrier under concrete is essential. Vapor barriers are a great way to keep moisture from getting into the concrete.

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

Vapor barrier permeability is expressed in perms.

Vapor barriers have varying numbers of permeability, expressed in perms. The better the number, greater permeable the information. Impermeable vapor barriers are the ones which has a rating of 0.1 perm or fewer while class II vapor retarders are the types which has a rating in excess of 0.1 perm much less than 1.0 perm.

You’ll hear people with all 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. On this page, we are while using term ‘vapor barrier’.

Why is an excessive amount of moisture in concrete a challenge?

One word: adhesives. Excessive moisture in concrete is a problem as it may cause pH changes that destroy adhesives. Here’s what happens.

As moisture makes its method to the surface of the layer of concrete, soluble alkalies show up for that ride and lift its surface pH above those of flooring adhesives. This makes the adhesives to breakdown and you get flooring failures such as swelling, bulging, or cupping.

Do you want a vapor barrier within concrete slab?

In a word, yes. Here’s why.

There’s usually 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 are available into experience of the bottom of a concrete floor via capillary action. Capillary action could be stopped by installing something referred to as a capillary break, a layer of crushed rock that goes relating to the subgrade and the slab.

Capillary breaks do a passable 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 needs to be something within the slab that prevents vapor moisture from entering.

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

How thick should a plastic vapor barrier be?

According to the Guide to Concrete Floor and Slab Construction authored by the American Concrete Institute, a vapor retarder should not be less than 10 mils thick. You may want a good thicker barrier though if you’re covering material with sharp angles.

Net profit: Vapor barriers must be strong enough so that they don’t easily puncture. If they do, moisture is certain to get in and that’s what you’re continuing to keep out.

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