Putting down a vapor barrier underneath your concrete slab is very important. In this video, master builder Matt Risinger shows us a job site with the 15 mil vapor barrier installed. The concrete will be poured directly over the vapor barrier. Risinger shows us that already on the site the vapor barrier has dew on it and the importance of that layer is that it will prevent that moisture from coming up through the concrete. Extremely porous, concrete soaks up moisture easily and it will spread out throughout the entire house. Seams are taped, penetrations are sealed. See the tape to get a better feel for how it works.