I need to put in a angle iron post, into a concrete block at the end of a driveway. I just checked, blocks are upright and just full of sand and dirt. It rained last night pretty good. Maybe a couple days to dry out? Looking at small amounts of pre mix concrete to use for the sign posts, maybe 6-8" deep. I have local Home Depot and Lowe's. most of the pre mix says it is good for inside and out. I guess this pre mix is most for tile work or repairs.