Description. Additional Information. Benseal Sodium Bentonite Clay for sealing marginal pond soils. Sold in full pallet of 48 - 50lb bags, 2,400lbs total. One 50lb bag = 0.7 cubic feet. Bentonite is a natural expanding clay sealant that when exposed to moisture can expand 15X or more creating a very effective pond sealant when applied correctly.