There are three grades of pressure-treated lumber. Above ground, contact with ground, and in ground, you can do further research on this on the internet. It is very difficult to get good lumber from Home Depot.
Dock pilings are even more saturated with pressure treating CCA... chromium copper and arsenic. Pressure treating changed to a different compound 10 years ago and drop the arsenic I forget all the particulars anymore.
The best four by fours are Cedar... Eastern red cedar to be more specific. I took down a 60 year old fence made of this. I saved the wood from the fence post and used it to make furniture. It was perfect.
All of this has to do with my soil type conditions. Your soil type may be more or far less harmful to Lumber than mine.
Setting a post. Tamp the bottom as best you can. Set a large flat bottom at the bottom of the hole. Begin back filling the hole with the spoils of the digging. Each 25% of the hole you backfill... verify Plumb and square each 25%. You can adjust plum bye camping the back fill dirt on the opposite side of lean.
IMHO... never dig a hole and fill it with wet concrete then shove a post into the concrete. This method hold water in the concrete recess and rots out the bottom of the post much much faster.
Structurally, concrete is not needed because you have a large-diameter Flat Rock for bearing. The time you save having to drive to the store to buy concrete and either dry bag... or mix would be better spent digging a good deep hole and tampng the bottom of your hole and tamping the dirt as you backfill.
Last edited by CashisKing; 07/24/20.
