Выражение встречается в следующем контексте:
The CONTRACTOR shall take particular care to ensure that the test cubes are stored under uniform conditions throughout the year, including a complete covering of damp sheet or similar approved material constantly sprayed with water while in the moulds and during any transit between Site and laboratory, and including subsequent storage immersed in water kept strictly within the specified temperature range.

Особо интересует перевод "damp sheet", ну, а если кто найдет силы и время для всего абзаца, тому ещё бОльшее спасибо!