OK, my two cents (sense?) worth: You should use coverings that allow the passing through of moisture. The best, if it can be afforded, is geotextile (I don't know the brand names). This is the material that is placed under the gravel of a road bed and used for riverbank stablization. If you are covering a previously sealed layer (clay covered) then I don't know... One local site used hay bales instead of sand bags to fill in excavation pits between seasons. Paul Morrissette [log in to unmask] Collections Technologist Canadian Heritage Professional and Technical Service Centre Winnipeg, Manitoba