I'm building a large deck, supported by posts planted in the yard, and I'm going in the direction of 6x6 treated posts (the entire deck and railing system is pressure treated, to be stained later).
My question is "What is the best way to anchor wood posts in a post hole?" I've heard that setting them in concrete doesn't work: the acid in the concrete causes the wood to break down, allowing water to penetrate, causing rot and decay.
Back on the farm, Dad taught me to set fence posts by placing a shovel-full (or two) of smaller stones in the bottom of the hole, then the post, and then only use dirt, fill the hole, tamping it tight all the way up. Would this method work for a large deck?
I am also interested in your opinions about cedar v. pressure treated posts. Which lasts longer?
Jacob, it's always better to put them up on something like a Simpson CB66 (column base for a 6X6) which is set on a raised concrete footing. The footing has to be sized for the weight it will carry. My average footings under the ground are 18 to 24" wide, and 18" deep.
If you need to put them into the ground for lateral resistance, then, put them in concrete, slope the top of the concrtete so that it sheds water away from the wood, and wrap this point with copper, which will stop the rot. If you do it this way make sure you make the bottom of the hole wide enough to act as a footing .. maybe 18", depending on the load the post will carry, and have at least 8" of concrete under the post.
Pressure treated is better, and put an un-cut factory end down rather than a cut end (no preservative).
If you're using the new ACQ pressure treated, make sure you use all stainless steel hardware and fasteners.
You know, I never put deck support posts into the ground. I only do this for pergolas, arbors and such, and then only in certain situations. Sorry to mis-lead you. A deck needs proper footings, specifically designed for your conditions.
If you use concrete footing and live in an area with any frost at all be sure to use Sonotubes or other cardboard forms because concrete in a hole has a rough enough surface the frost will grab the sides and push it up.
I normally use a 12" hole and pour dry ready-mix in the hole or drop a pre-formed concrete "cookie" in the bottom of the hole and tamp the dirt down around the post. I tend to set a lot of posts to carry the load since my posts come up for the railing also. But I'm thinking about pouring piers like joe but I've never had a problem with the way I've been using