Installing a Vapor Barrier Underneath Concrete Slab

What You'll Need
Metal Scraper
Plastic Vapor Barrier
Screened Gravel
Duct Tape
Utility Knife

Any home that is built on a concrete slab is going to need to have a vapor barrier installed. The vapor barrier covers the ground underneath the concrete slab in order to protect the home from any type of moisture from seeping through the porous concrete and into the home. The vapor barrier is essential to eliminating water damage, mold growth, and in keeping the basement, or ground floor dry. Installation of the vapor barrier is done after the concrete footings and utilities are completed.

Step 1: Prepare Footings for Plastic

The one problem with any type of plastic vapor barrier is that they can rip easily during installation, pouring of slab, or through any downtime between the footing and the pouring. One way to protect the vapor barrier is to scrape the footings to make sure that they are smooth. This is time consuming, but is required for the overall health of the vapor barrier as well as the home. On larger footings, a Bobcat with a steel skid can help to smooth out the rough portions of the footing.

Step 2: Prepare Utilities

Before the actual concrete slab is poured the utilities and plumbing are brought into position. They must be protected from the gravel that will be laid, as well as the concrete when it is poured. Wrap them with plastic and tape. Make sure that they are well covered so nothing will be able to get into the pipes or electrical components.

Step 3: Install Vapor Barrier

The black plastic vapor barrier is the next part of the process. Start at the edge of a footing and roll out the plastic along the length of the home. Tape the plastic in place and place some rocks, or other weighty objects, onto the edges to keep it stationary. As you continue to roll out the vapor barrier, tape the seams together with duct tape. Overlap each of the seams by 6 to 8 inches to make sure that there is coverage under the entire concrete slab. As you are working on the vapor barrier be careful where you step so that there isn't any tears being made in the plastic. If you do tear the plastic, simply tape a new piece over it.

Step 4: Cut Opening for Utilities

As the vapor barrier is being rolled out simply cut small openings in the plastic for the different utilities. A utility knife makes this process very easy. Wrap the plastic around pipes to create a moisture-proof barrier.

Step 5: Install Gravel

As a final part of the process, you want to give the cement slab a firm, compact foundation so there isn't any cracks in the future. Have a load of screened gravel delivered to the area where the foundation is going to go. Spread the gravel on top of the vapor barrier to a 6 inch depth. Make sure there aren't any high spots or bare areas. Rent a compactor and run it over the surface until the gravel is tight and stable.