How to Replace a Deck Post
If you have a rotten or damaged post supporting your porch or deck, it needs to be replaced. The first step is to remove the old post. Once that is done, you can set a new post in concrete to ensure that your porch or deck doesn’t sag.
Always use pressure-treated wood for replacement posts and set them in concrete poured over a gravel base, to keep water away from the bottom and sides of the post. The gravel will drain the water away from the bottom of the post and the concrete will buffer it from water-soaked soil.
There are two ways to put concrete into a post hole; the traditional method is to use wet concrete — a combination of Redi-Mix and water. After you add the water to the Redi-Mix and work the water in, you haul it with a wheelbarrow to the post hole. Then you pour in the wet concrete. The second method, described below, is much easier because you’ll be pouring dry Redi-Mix into the hole, which is already filled with water. It’s a lot faster than the old method and isn’t such backbreaking work.
Whether you have several posts or just one, the easiest and cheapest concrete comes in bags of Redi-Mix concrete. They're available in different-sized bags and have the sand, gravel, and cement already mixed together. You add water to the mix to make concrete, mixing it in a tub or child’s swimming pool, and use a wheelbarrow to haul the wet concrete to the post hole.
Here’s how to set posts using the dry-mix method. You need gravel, one or more bags of premixed concrete — depending on how many posts you are replacing — water, and the posts. To set the posts:
Pour at least 4 inches of gravel into the bottom quarter of each hole.
The gravel serves as a drainage area so the post doesn’t sit in water when it rains.
Set the post in the gravel in the hole and line it up with other posts.
Make sure the bottom of the post, at ground level, is in line with the other posts.
Add dry premixed concrete until the hole is half full and then add water up to the top of the hole.
Some water will soak in or run off, the rest will get the concrete wet. You won’t have to add any more water.
Level the post as you want it.
Add dry premixed concrete until the hole is full.
The concrete displaces excess water so you may see some more water running out of the hole.
Using a trowel, smooth out the surface and slope the concrete down toward the ground.
That allows water to flow right off without standing against the wood.