Just what is a concrete vapor barrier?

A concrete vapor barrier is any material that forestalls moisture from entering a concrete slab. Vapor barriers are utilized because while fresh concrete flows wet, it’s not designed to stay that way. It requires to 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 understand the sort of damage that too much moisture may cause. Moisture enters concrete in a number of ways, including through the ground, from humidity in mid-air, and through leaky plumbing that goes through a slab. Of course, there’s 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 connection with a source of moisture, you’re gonna have problems. This is why a vapor barrier under concrete is essential. Vapor barriers are a good way to maintain moisture from engaging in the concrete.

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

Vapor barrier permeability is expressed in perms.

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

You’ll hear people with all the terms ‘vapor barrier’ and ‘vapor retarder’ interchangeably. However, as it happens, they aren’t a similar thing. Vapor barriers are less permeable than vapor retarders. In this article, we’ll be while using term ‘vapor barrier’.

Why’s a lot of moisture in concrete a problem?

A word: adhesives. Too much moisture in concrete is a concern as it may cause pH changes that destroy adhesives. Here’s what are the results.

As moisture makes its method to the counter of a concrete slab, soluble alkalies show up for your ride and raise its surface pH above that relating to flooring adhesives. This causes the adhesives to breakdown and you get flooring failures such as swelling, bulging, or cupping.

Do you really need a vapor barrier under a concrete slab?

In short, yes. Here’s why.

There’s typically water underneath a structure site. It might not be near the surface, but that doesn’t mean it’s not there. This water can progress over the soil and are avalable into experience of the base of a concrete floor via capillary action. Capillary action may be stopped by using something called a capillary break, a layer of crushed rock which goes between your subgrade and also the slab.

Capillary breaks do a good 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 ought to be something beneath the slab that prevents 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 within their installation guidelines.

How thick should a plastic vapor barrier be?

In line with the Help guide Concrete Floor and Slab Construction provided by the American Concrete Institute, a vapor retarder should not be under 10 mils thick. You need a good thicker barrier though if you’re covering material with sharp angles.

Bottom line: Vapor barriers need to be sufficiently strong so they don’t easily puncture. If they do, moisture will get in and that’s what you’re trying to keep out.

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