Things You'll Need
Drill with mixing paddle
Galvanized post base
Galvanized post top bracket
Deck post (same size as existing)
Sonotube same diameter of the existing footing hole
10D joist hanger nails
Heavy-duty floor jack
Building a deck can require a large monetary investment. A properly constructed deck should provide years, if not decades, of useful service. They sometimes can require repair, and a common repair -- especially in northern climates -- is removing and replacing the concrete footings. If improperly mixed and poured, concrete can become brittle and crack due to frost and ground movement. Crumbling footings causes decks to sag and sink. Footings can be replaced to restore your deck to a level -- and safe -- condition.
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Place some scrap lumber under a floor jack, then cut a post that will fit between the floor jack and the beam of the deck. Remove the nails that attach the existing post to the post base and jack up the deck until it is level.
Put scrap lumber down under the base of the post jack, then extend the post jack until it is touching the bottom of the deck beam. Lower the floor jack until the post jack is supporting the weight of the deck. Remove the nails securing the existing post to the beam and take out the beam. The weight of the deck at this location is now supported by the post jack.
Break up the old footing with a jackhammer and remove the pieces from the hole by hand and with a post-hole digger. Keep breaking up the concrete a little at a time and remove the concrete until all of the concrete is out of the footing hole.
Put the new sonotube into the footing hole. Mix new concrete in the proportions specified on the bag and pour it into the sonotube, filling it to the top. Let the concrete cure for at least one day.
Install a new galvanized post base to the new concrete footing with a concrete anchor.
Recheck that the deck is level, then measure from the post base to the bottom of the deck beam where the new post will attach. Level the deck with the floor jack if necessary.
Cut a new deck post to the length you measured in the previous step. Install the post in the post base with 10D joist hanger nails, then attach the top of the post to the beam with a new galvanized post-to-beam bracket using 10D joist hanger nails. You may need to jack up the beam slightly to get the post in, then let it down.
Measure the depth and width of the footing hole when you dig out the old concrete to ensure that it meets building codes. If not, dig out the hole until it meets code requirements.
Do not let anyone on or around the deck while this repair is under way. The post jack is only in place as a temporary support until the new concrete can cure and the new post installed.