Just 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 likely to stay that way. It needs to dry then stay dry to stop flooring problems.
If you’ve been able to a problem with a basement floor (or any concrete floor), you understand the sort of damage that as well much moisture can cause. Moisture enters concrete in a number of ways, including via the ground, from humidity in the air, and thru leaky plumbing that goes through a slab. Naturally, there’s the moisture that's in 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 connection with a resource of moisture, you’re planning to have issues. That is why a vapor barrier under concrete is essential. Vapor barriers are a good way to hold moisture from getting into the concrete.
Note: A vapor barrier is not just like an underlayment. However, you can find underlayments that work as vapor barriers.
Vapor barrier permeability is expressed in perms.
Vapor barriers have varying examples of permeability, expressed in perms. The higher the number, the harder permeable the fabric. Impermeable vapor barriers are those using a rating of 0.1 perm or fewer while class II vapor retarders are the types which has a rating higher than 0.1 perm and much less than 1.0 perm.
You’ll hear people while using the terms ‘vapor barrier’ and ‘vapor retarder’ interchangeably. However, strictly speaking, they aren’t the same thing. Vapor barriers are less permeable than vapor retarders. In the following paragraphs, we are while using the term ‘vapor barrier’.
Why is excessive moisture in concrete a difficulty?
A word: adhesives. An excessive amount 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 method to the top of an layer of concrete, soluble alkalies come along for that ride and lift its surface pH above that of flooring adhesives. This causes the adhesives to breakdown and also you end up with flooring failures for example swelling, bulging, or cupping.
Do you need a vapor barrier within layer of concrete?
In a word, yes. Here’s why.
There’s more often than not water underneath a building site. It may not be at the surface, but that doesn’t mean it’s not there. This water can go up from the soil are available into contact with the base of a concrete floor via capillary action. Capillary action can be stopped by installing something called a capillary break, a layer of crushed rock which goes between the subgrade and also the slab.
Capillary breaks do an adequate job of stopping water in the 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 should be something underneath 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 within their installation guidelines.
How thick should a plastic vapor barrier be?
In accordance with the Self-help guide to Concrete Floor and Slab Construction created by the American Concrete Institute, a vapor retarder really should not be lower than 10 mils thick. You need a level thicker barrier though if you’re covering material with sharp angles.
Bottom line: Vapor barriers have to be strong enough so they don’t easily puncture. If they do, moisture are certain to get in and that’s what you’re continuing to keep out.
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