What is a concrete vapor barrier?
A concrete vapor barrier is any material that forestalls 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 doing this. It must dry then stay dry to stop flooring problems.
If you’ve had a problem with a basement floor (or any concrete floor), you realize the type of damage the exact same thing much moisture might cause. Moisture enters concrete in a number of ways, including through the ground, from humidity in the air, and thru leaky plumbing that goes through a slab. Naturally, there’s and also the moisture that has been 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 experience of a source of moisture, you’re going to have issues. This is why a vapor barrier under concrete is vital. Vapor barriers are a great way to keep moisture from engaging in the concrete.
Note: A vapor barrier is not identical to an underlayment. However, you will find underlayments that act as vapor barriers.
Vapor barrier permeability is expressed in perms.
Vapor barriers have varying levels of permeability, expressed in perms. The greater the number, greater permeable the information. Impermeable vapor barriers are the ones using a rating of 0.1 perm or fewer while class II vapor retarders are the ones which has 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. Vapor barriers are less permeable than vapor retarders. In this article, i will be using the term ‘vapor barrier’.
Exactly why is an excessive amount of moisture in concrete a problem?
One word: adhesives. A lot of moisture in concrete is an issue since it could cause pH changes that destroy adhesives. Here’s what goes on.
As moisture makes its way to the outer lining of an layer of concrete, soluble alkalies show up for the ride and raise its surface pH above that relating to flooring adhesives. This causes the adhesives to breakdown and you end up having flooring failures including swelling, bulging, or cupping.
Do you really need a vapor barrier within a concrete slab?
In short, yes. Here’s why.
There’s more often than not water underneath a structure site. It may not be at the surface, but that doesn’t mean it’s not there. This water can progress up through the soil and are available into connection with the base of a concrete floor via capillary action. Capillary action could be stopped by installing something known as a capillary break, a layer of crushed rock which goes between the subgrade as well as the slab.
Capillary breaks do a sufficient 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 concrete slab. Therefore, there must be something underneath the slab that stops vapor moisture from entering.
There is also a vapor barrier for liability reasons because most manufacturers of flooring include vapor barriers or retarders inside their installation guidelines.
How thick should a plastic vapor barrier be?
According to the Help guide to Concrete Floor and Slab Construction created by the American Concrete Institute, a vapor retarder shouldn't be below 10 mils thick. You need an even thicker barrier though if you’re covering material with sharp angles.
Main point here: Vapor barriers must be sufficiently strong in order that they don’t easily puncture. If they do, moisture can get in and that’s what you’re always keeping out.
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