Which statement is true regarding the use of a 3 inch thick layer of manufactured sand on the vapor retarder?

• A. It is placed on the vapor retarder before concrete placement
• B. It is placed on top of the slab after curing
• C. It is skipped when sulfate exposure is not a concern
• D. It is used only in high humidity environments

Answer: (A)

The key idea is protecting the vapor retarder while creating a stable base for the slab. A 3-inch layer of manufactured sand is placed directly on top of the vapor retarder before the concrete is poured. This sand layer cushions the vapor barrier, reducing the risk of puncture or damage from aggregate, rebar, or equipment during placement, and it provides a smooth, level surface for the concrete to sit on. It also helps establish a consistent thickness and can act as a capillary break beneath the slab, improving moisture control pathways without altering how the concrete cures. Placing the sand after curing would fail to protect the barrier during placement, skipping it when sulfate exposure isn’t a concern misses the protective role it plays regardless of sulfate, and it isn’t about humidity conditions.