I'm trying to determine how much concrete I'll need to set fence posts for a 6ft tall privacy fence. From what I've read these are the parameters I'll be using for each post hole.
Post: 4in x 4in x 8ft
Hole Diameter: 12in
Hole depth: 30in (6in of gravel + 24in for post)
When I calculate the concrete needed, do I use the 30in depth or just the 24in for the part of the post in the ground? At the moment I plan on using 3-50lb bags of sakrete fast drying per hole. Is this too much, too little, or just enough?
Well, I always use fast setting fence post concrete and you put 2" of gravel on the bottom of the hole, then fill the hole 1/3 of the way up with water, dump one bag of fence post concrete and level the post, then hold it that way for 2 minutes and let dry overnight. The reason fence post concrete is different is that it is packaged to be one bag per post based on a 12-18" hole diameter and a 4x4 post, no pre-mixing, fast setting.
I am kind of partial to J. Raefield and J Stewarts methods. Very simple and straight forward. I too think 12" is too much although some deck standards for posts are 12". I plan on using 8" on the three posts I have to dig in my deck rebuild. Hoping the code officer lets me go with 8" vs 12"!? Also I plan on using 8" Sonotubes and filling it to the top of a 48" tube height set in the ground to a depth of between 36" and 42". Which when I did the calculations it became 2 bags per tube or about 3.1 yards of concrete for the three piers I need. It is suggested you have it delivered when its over 2 yards which I feel is less work but worth the extra costs.