Cutting Edge Insights
with Dr. Lee

Dr. Lee on Location – Vapor and Slabs

Concrete is tough so it doesn’t matter what is beneath a slab of it, right?


Concrete has a property of being porous to water in the vapor phase.

If you don’t think about that, you can inadvertently cause mold to grow under a finished floor.

The structure’s occupants may not become ill, but air quality will be affected and the occupiable space will not be a healthy one.

6 mil plastic (0.006 inch thick) is commonly used as a vapor barrier.

Here is an example of a recent project in my world:

Does the vapor barrier need to be continuously sealed to the vapor barrier on either side of it? No – simply get it as close as possible. With vapor control, 99% continuous is 99% effective.

With bulk water control, if I were 99% effective on my 15,000 sq ft building, I’d have a 150 square foot hole in my roof – no good at all!

But vapor is different.

Watch the video below to learn some of the finer points about vapor, slabs, and tying a slab into an existing slab.

Let me know what questions you may have.

Until next time,

Dr. Lee Newton

How A Doctor Learned To Develop Real Estate

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