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Just what concrete vapor barrier?

A concrete vapor barrier is any material that stops moisture from entering a layer of concrete. Vapor barriers are widely-used because while fresh concrete is poured wet, it’s not designed to stay like that. It needs to dry and then stay dry to prevent flooring problems.

If you’ve been able to an issue with a basement floor (or any concrete floor), you know the level of damage that too much moisture may cause. Moisture enters concrete in many different ways, including through the ground, from humidity in mid-air, and through leaky plumbing that goes through a slab. Obviously, there’s 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 exposure to a source of moisture, you’re going to have problems. This is the reason a vapor barrier under concrete is crucial. Vapor barriers are a way to keep moisture from engaging in the concrete.

Note: A vapor barrier isn’t the comparable to an underlayment. However, you’ll find underlayments that become 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 material. Impermeable vapor barriers are the type using a rating of 0.1 perm or less while class II vapor retarders are the ones having a rating higher than 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 the same thing. Vapor barriers are less permeable than vapor retarders. In the following paragraphs, we are while using term ‘vapor barrier’.

Exactly why is an excessive amount of moisture in concrete a difficulty?

One word: adhesives. Excessive moisture in concrete is an issue because it may cause pH changes that destroy adhesives. Here’s how are you affected.

As moisture makes its strategy to the outer lining of an concrete slab, soluble alkalies come along for your ride and lift its surface pH above that of flooring adhesives. This makes the adhesives to breakdown and you get flooring failures for example swelling, bulging, or cupping.

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

In a word, yes. Here’s why.

There’s almost always water underneath a structure site. It may not be close to the surface, however that doesn’t mean it’s not there. This water can progress over the soil and are available into connection with the bottom of a concrete floor via capillary action. Capillary action can be stopped by using something referred to as a capillary break, a layer of crushed rock which goes relating to the subgrade along with the slab.

Capillary breaks do a sufficient 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 ought to be something beneath the slab that stops vapor moisture from entering.

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

How thick should a plastic vapor barrier be?

In accordance with the Guide to Concrete Floor and Slab Construction created by the American Concrete Institute, a vapor retarder shouldn’t be under 10 mils thick. You will need an even thicker barrier though if you’re covering material with sharp angles.

Important thing: Vapor barriers need to be sufficiently strong enough so they really don’t easily puncture. Whenever they do, moisture will get in and that’s what you’re continuing to keep out.

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