I'm in the process of laying a concrete slab for the base of a outdoor store with two compartments. One for storing my daughters play equipment and the other for storing chopped wood for the wood burner. I've got a roll of DPC to lay under the blocks, but has anyone got any advice on damp proofing the rest of the slab? I have two ideas. 1. Painting the concrete with bitumen before screeding with a sand cement mixture. 2. Mixing the screed with a waterproofing admix before laying. Any thoughts out there on either method.