What is a concrete vapor barrier?
A concrete vapor barrier is any material that stops moisture from entering a layer of concrete. Vapor barriers are used because while fresh concrete flows wet, it’s not designed to stay like that. It must dry and then stay dry in order to avoid flooring problems.
If you’ve been able to a problem with a basement floor (or any concrete floor), you realize the sort of damage this too much moisture could cause. Moisture enters concrete in many different ways, including using the ground, from humidity in mid-air, and throughout leaky plumbing that goes through a slab. Naturally, there’s also the moisture that has been from the original concrete mixture.
There’s only one-way moisture leaves concrete, though, and that’s via its surface. When you have a concrete floor that’s in continuous exposure to a resource of moisture, you’re planning to have issues. That is why 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 same as an underlayment. However, there are underlayments that become vapor barriers.
Vapor barrier permeability is expressed in perms.
Vapor barriers have varying levels of permeability, expressed in perms. The higher the number, the harder permeable the pad. Impermeable vapor barriers are the ones with a rating of 0.1 perm or less while class II vapor retarders are those with 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, strictly speaking, they aren’t the same. Vapor barriers are less permeable than vapor retarders. In this post, we will be while using the term ‘vapor barrier’.
Why is an excessive amount of moisture in concrete a problem?
One word: adhesives. Excessive moisture in concrete is a problem given it could cause pH changes that destroy adhesives. Here’s what happens.
As moisture makes its approach to the outer lining of your layer of concrete, soluble alkalies appear for your ride and lift its surface pH above those of flooring adhesives. This will cause the adhesives to breakdown so you end up getting flooring failures such as swelling, bulging, or cupping.
Do you want a vapor barrier with a layer of concrete?
In short, yes. Here’s why.
There’s more often than not water underneath a building site. It might not be close to the surface, however that doesn’t mean it’s not there. This water can progress up through the soil and are avalable into connection with the foot of a concrete floor via capillary action. Capillary action can be stopped by using something called a capillary break, a layer of crushed rock that goes relating to 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 concrete slab. Therefore, there ought to be something within the slab that forestalls vapor moisture from entering.
You have 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 Help guide Concrete Floor and Slab Construction provided by the American Concrete Institute, a vapor retarder really should not be under 10 mils thick. You may want a much thicker barrier though if you’re covering material with sharp angles.
Net profit: Vapor barriers should be strong enough so they really don’t easily puncture. When they do, moisture will get in and that’s what you’re always keeping out.
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