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

For conducting a moisture test on a concrete slab, the use of polyethylene is standard practice due to its effectiveness in preventing moisture from escaping. Polyethylene is a durable plastic material that acts as an impermeable barrier, which allows for an accurate assessment of the moisture level within the slab. When polyethylene is taped securely to the surface, it traps any moisture that might evaporate from the concrete beneath, creating a controlled environment for the test.

Moreover, polyethylene is widely available and resistant to moisture, making it suitable for this kind of application. It can easily be cut to the required size and shapes, ensuring a good seal for the test duration.

Other materials mentioned in the options may not provide the same level of effectiveness. For example, clear plastic wrap might not be thick enough to prevent moisture loss effectively over an extended testing period. Cardboard would absorb moisture instead of trapping it, which would skew the test results. Wooden boards, while solid, can also absorb moisture or permit it to escape, thereby affecting the integrity of the moisture reading. Therefore, polyethylene is the preferred choice for moisture testing on a slab, ensuring reliable and valid results.