What material should be taped off to the slab for a moisture test?

Polyethylene is the correct material to be taped off to the slab for a moisture test because it is impermeable to moisture and serves as an effective barrier. In moisture testing, a sheet of polyethylene is often placed directly on the concrete slab and sealed around the edges with tape. This setup allows for an accurate assessment of moisture permeability by trapping moisture that may be present in the concrete underneath the sheet. The test typically involves observing the condensation that may gather on the underside of the polyethylene over a specified period, which informs contractors about the moisture levels in the substrate.

Using materials like vinyl, wood, or cement board for this purpose would not provide the same level of reliability, as they can allow moisture to pass through or may not adequately seal to the slab, thereby skewing the test results. Polyethylene’s characteristics make it the ideal choice for ensuring that moisture levels are measured accurately and effectively.