Hi Howard,

We would not suggest using Postcrete for this project as there is no guaranteed compressive strength. It is ideal for fence posts and smaller applications such as small gateposts and rotary lines however not to support sheds or similar structures. In this instance we would suggest our Multi Purpose Concrete or High Strength Concrete. Both are ready to use however not quick setting like Postcrete (normally 2 -3 hours)

The size of the hole is dependent on the posts but would suggest narrow and deep with approx 25% of the post below ground.