Our mailbox post got rotten over fifteen years of being in the ground. The post had to be replaced. @ibt helped me with the project. I dug out the old concrete and prepped the hole for quick dry concrete.
We got a new post at Home Depot and had to cut it as it was a little too long and did not match the other homes. @ibt measured another person's mailbox near by and we set our height to the same as theirs.
Once we measured and cut the pole and got to mixing the quick set concrete. Using a shovel and wheelbarrow works well.
We got the consistancy to our liking mixing water in with the concrete mix. And eventually it was ready to pour into the hole.
Once the mailbox post was placed in the hole with the concrete. We sured it up with stakes and cuts of wood to secure the mailbox post in place and to make sure its level.
We moved the old mailbox over to the new post and it was ready for another decade of use. The mailbox post is pressure treated and was quite heavy. Should repel the weather for many years to come.