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Some Guy

wrote:

going to use 10 treated 4x6 posts as foundation for 10x12 shed.....

4 x 6 posts?

Are they square? Do you mean 4 x 4 or 6 x 6 posts?

So you're not going to have a poured concrete pad or floor for this
shed?

guy at menards sugested coating with tar to extend life.

He might mean creosote. Paint the in-ground portion with creosote
(several coats) - let it dry in the sun between coats.

sounded like good idea to me...

I've done it. Wood posts (6" x 6") set into 1-foot diam. concrete posts
(piers) set 4 feet in the ground.

also building inspector guy advised me not to concrete posts
in ground or frost will be problem.....dig holes 48" then
concrete in bottom of hole and posts sit on the concrete...
.sound OK? Thanks

What is the frost line in your area? 4 feet is about the deepest you
need to go in northern US and Canada except possibly Alaska.

You can do 10" holes (12" if necessary), get cardboard sono-tubes, set
your creosote-painted posts in the holes and then pour concrete. Have
the top of the concrete come to at least 2" above grade - 6" is better.
Throw some 1/2" rebar into the concrete (2 or 3 pieces, each one 4-ft
long). That will make it indestructable.

Mix the concrete properly. NOT TOO SOUPY. USE AS LITTLE WATER AS YOU
CAN. CLEAN SAND AND CLEAN 1/2" CRUSHED STONE.

Use a tamper (or rent a vibrator) to properly place the concrete
(important when you minimize the water content).

All concrete shrinks when it cures. The more water you use, the more it
shrinks. A concrete pier shrinking around a wood post will result in
cracks radiating from the corners of wood post. The rebar will help
hold the pier together if that happens.

The concrete will also protect the wood post from rotting. But only if
you properly mix and place the concrete. If you just throw some cement,
sand and stone in the hole (or the pre-mixed concrete stuff) and pour
some water on it, you'll just end up with ****.