Quikrete Fast-Setting Concrete Mix 50 lb QUIKRETE® Fast-Setting Concrete Mix (No. 1004) is a special blend of fast-setting cements, sand and gravel designed to set hard in approx. 20 to 40 minutes. Sets posts without mixing. Pour dry mix into hole and soak with water.Use for Setting:Fence postsMailbox postsBasketball postsDeck postsLamp postsSwing sets Use for Building:StepsSidewalksConcrete appliance pads