How to Form a Slab Recess Without Damaging the Vapor Barrier

Place a vapor barrier sheet across the soil. Verify that the sheet covers the entire area for the future structure. Use multiple sheets, if necessary. Overlap the vapor barrier's edges so that moisture cannot seep through open gaps.

Cover the vapor barrier sheets with a layer of sand or gravel. The job site's engineer will need to determine the type of sand or gravel needed, based on regional soil composition and weather.

Enclose the entire vapor barrier area with 2-inch by 4-inch planks (2x4s). Lay the wood on its edge, creating a short wall structure for retaining the wet concrete. Nail the wood pieces together at their connection points along the vapor barrier's edge with a hammer.

Enclose the intended recess area with 2x4s, attaching them as directed in Step 3.

Pour concrete into the larger enclosed area until the level reaches just below the wood's top edge.

Pour concrete into the enclosed recess area. Fill the area halfway, as opposed to filling the area completely, as in Step 5.

Allow all the concrete to cure before removing the wood planks. The sand, or gravel, will protect the vapor barrier from any poured concrete damage. The vapor barrier will remain intact and secure once the concrete cures and hardens.