Designed to work with small batches of concrete as a strengthener (increasing strength by up to 23%, the maker says), hardener, and waterproofing agent, Super-Krete’s Concrete Boost reportedly reduces permeability, efflorescence, and freeze/thaw susceptibility. Use it with a ready-mix sack (up to 90 pounds) of any Portland cement–based material. A 12 pack costs $17.85. super-krete.com