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Repairing the Base of a Rotted Deck Post

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The Backstory - The Bad News

In 2019, my father-in-law and I worked on a large home improvement project. We designed and built a large, wrap-around deck as a continuation of my old deck. During that project, we unearthed a disaster waiting to happen.

When the deck was originally built with the house around 2007, we found they made the footers by hand digging large holes and filling them with concrete. They put the deck posts 6" deep into the wet concrete. When the concrete hardened, they covered those footers with 5" of dirt, which looked nice and made the dirt level with grade. Over the next 12 years, the rainwater draining from the downspout next to a post slowly rotted away the cedar. The 6x6 post was now a 4x4 post and was continuing to rot.

Rotted 6x6 Deck Post Now Only 4x4

Rotted 6x6 Deck Post Now Only 4x4

We decided to press on with the deck project and wait until the next year to repair the post. Fast forward to the spring of 2020 and I had a lot of time on my hands during the Covid-19 pandemic. It was time to fix the post. After praying for wisdom and safety to the Lord for the project, I ran my plans by my wife's father and uncle. I'm thankful to all three for their advice.

My Kingdom for a Code

This section is a bunch of boring information on building codes and why we have these problems of rotting deck posts. If you don't care about this useful, but boring information please skip to The Plan section below.

Back in 2007, the Prescriptive Residential Deck Construction Guide based on the 2006 International Residential Code was in effect. That code allowed for posts to be buried below ground. But even the best prescribed solution had the posts sitting in a pre-manufactured post base on the concrete footers flush with the ground where they could more easily rust.

Please note that at the time of my deck's construction, the code never allowed for a post to be buried inside the concrete footer where water could seep down and stay, causing it to rot faster and faster.

Prescriptive Residential Deck Construction Guide based on the 2006 International Residential Code

Prescriptive Residential Deck Construction Guide based on the 2006 International Residential Code

Nowadays, while the code does allow for some posts to be buried, the majority of the options available require the tops of the footers to be above grade. A post can even be put inside the concrete, but the concrete must be above the dirt grade and the footer must be rounded on top to allow water to easily drain away.

Prescriptive Residential Deck Construction Guide based on the 2015 International Residential Code

Prescriptive Residential Deck Construction Guide based on the 2015 International Residential Code

A Code Within a Code

Some cities have amended the building code requirements. In my small city, our codes are very specific and require that the concrete footers be 6" above grade, be rounded on top to allow the shedding of water and the post must be attached to the top of the footer with a pre-manufactured, galvanized post base that is 1" in height to keep the post from touching any standing water. It also requires a rebar reinforcement inside the concrete. While this code may seem extreme and a lot of extra work, it means a deck made today will probably be standing strong in 30 or 40 years.

Special Building Code for Deck Footers in My City

Special Building Code for Deck Footers in My City

The Plan

I wanted to solve the problem of the rotted post, make the deck safe again and bring the footer up to code as much as possible without tearing everything out. The plan was to cut the post 7" above grade, attach a 1" post base and pour more concrete under the base to raise the footer to 6" above grade, meeting the post base.

repairing-the-base-of-a-rotted-deck-post

Brace for Impact!

Before I could start, I had to brace the deck to keep it in place when the post was cut. In my case, there was a roof over the deck increasing the weight, so the brace had to be very strong.

I started by screwing together two 2x6 boards to make a beam. I toenail screwed it up to the joists under the deck and used some 6" structural lag screws to hold the beam against the posts. Finally, I used 2 1/2" lag screws to mount the beam to the posts with L brackets.

repairing-the-base-of-a-rotted-deck-post
repairing-the-base-of-a-rotted-deck-post

I used two bottle jacks to lift 4x4 posts against the beam to hold it in place. Experience taught me to:

  1. Use concrete pavers on dry ground for a solid base.
  2. Screw a piece of 2x4 to the bottom of the 4x4 to keep it from splitting.
  3. Screw the top of the 4x4 posts to the beam to keep them from moving.
  4. Use a lateral brace to keep the 4x4 posts from moving.
repairing-the-base-of-a-rotted-deck-post

A Cut Above the Rest

I dug completely around the footer, exposing it a few inches and leaving a good amount of room to work. Before cutting, I used a level to make sure I knew the beginning slope of the deck. Then I marked the post 7" above grade with a line on all 4 sides and clamped a speed square to the post to use as a guide to keep the saw straight when cutting. A circular saw was then used to cut around the post. When I was done, a 1" square piece remained in the middle of the post. I was amazed that small piece of wood continued to hold up the deck and roof.

I used a reciprocating saw with a long blade to cut through the remaining wood in the post. The post collapsed on the blade and the deck/roof gave a loud crack after the last millimeter of wood was cut, holding it firmly in place. My kids rushed outside with excitement and concern over the loud crack they heard inside. The entire piece could not have dropped more than 1/16 of an inch, so I knew nothing was damaged. I released the blade from the saw and set the saw aside. I pumped the bottle jacks several times which lifted the deck slightly, made it level again and the blade could be removed.

I used the reciprocating saw to cut the very bottom of the post by the concrete footer and pulled out the 11" piece of post. I anticipated the removal of the post in the footer would take hours, but it was so rotted I was able to pull it out by hand! I was so thankful that I didn't have to work for hours cutting and chipping out the post from the footer. At the same time I realized how bad of a situation this was.

Rotted Post Which Used to be a 6x6

Rotted Post Which Used to be a 6x6

Post Piece Pulled from Footer

Post Piece Pulled from Footer

Scrub a Dub Dub


I spent a good amount of time cleaning the footer. Using a small shop vac and scraping tool, I removed all the dirt I could on top of and in the hole in the footer. Then I used a garden hose with the nozzle set to fine spray to get the rest of the dirt off. The shop vac was used to clean the remaining muddy water from the footer.

Dirty Footer

Dirty Footer

Clean Footer

Clean Footer

Tubular, man! Tubular!

To hold the concrete that would be poured on top of the footer, a concrete form tube was used. Each store sells their own brand, but they are all a heavy cardboard tube with a waxy coating inside. I got mine from Menards, so it is called a Sonotube. They come in various lengths and need to be cut to size. I used a marker to draw a black line around the tube to give me an 11" length. A jigsaw was used to cut through the cardboard tube, but a hand saw could have been used as well.

I put the piece of Sonotube on top of the footer and used a 2' level to see where it was not level. I took away the Sonotube and chipped away at the concrete footer with an old hammer where it needed to be lowered. I kept chipping away at the footer and checking until the tube was level. Some concrete chips had to be put under part of the sonotube to raise it as well. At that point, I put the Sonotube aside to be used later.

A Drilling Experience

To hold the old concrete footer to the new concrete that would be poured, I had to put a rebar structure in place. The structure consisted of 4 vertical rebar rods placed into 3" deep holes drilled into the existing footer. The rebar rods would extend up to 2" from the top of the new concrete footer. A rebar square would be wired near the top of the rebar rods.

As a little background, our code required #4 (1/2") vertical rebar rods. You can pick up rebar from local hardware stores like Menards in short lengths and then cut to your needs with a cutting blade in a circular saw. The squares were made from #3 (3/8") rebar and are hard to bend. I suggest contacting your local concrete supply store for pre-made squares.You can also Google "rebar squares" to find suppliers.

I put the rebar square on the old footer and used it as a template. In the inside corners of the square I drilled holes into the footer with a hammer drill using a good 5/8" masonry bit to the depth of 3". The 5/8" hole allowed the 1/2" rebar to easily fit into the hole. The shop vac was used to clean up the concrete dust. To get the dust out of the 3" holes, I took a soda straw and held one end inside the vac hose, cupping my hand around it to hold it in place, seal it and direct the vacuum force through the straw. The straw was put into each hole to suck out the dust and debris.

To hold the rebar in the old footer, I used a concrete anchoring adhesive called Sika Super Strength Anchoring Adhesive from Lowes. It was actually an expensive epoxy that came in a tube that fit in my standard calking gun and every home improvement store carries an equivalent brand. For best results, I squeezed the adhesive into ONE 3" hole to about 3/4 full. Then I pressed the rebar rod into the hole, twisting back and forth slightly as it went down. As it did go down, the level of the adhesive went up to leave a nice ring around the top of the hole. Then I moved on to the next hole. The epoxy adhesive hardens FAST. It is very important to work on ONE hole at a time.

repairing-the-base-of-a-rotted-deck-post

An Uplifting Time

You might be asking why I went to all this trouble. Why not just pour the new concrete on top of the old concrete and be done with it? The answer is, "uplift". On a very windy day, under the right conditions, the wind can blow under the deck or roof structure and lift the deck up if it is not anchored properly. If rebar is not used to anchor the old footer to the new concrete, the deck could lift up and crash down.

A Bolt of Inspiration

In a normal deck footer installation, concrete is poured into a Sonotube and then a J bolt is placed in the center of the poured footer with about 3/4" exposed at the top. When the concrete hardens, the post bracket is put over top of the exposed bolt and held in place by a nut that is ratcheted down. The post is then put in the bracket and screwed tight to it.

repairing-the-base-of-a-rotted-deck-post

What is a J bolt and why use it? It is a long, hot dipped, galvanized steel bolt that is straight on the threaded end and is bent on the hooked end to look like a J or L. The J portion is pushed into the wet concrete. When dried, the concrete holds the bolt firmly in place, especially around the J. In the event of an updraft, the post bracket would try to pull the J bolt out of the concrete, but it would stay in place. If a regular straight bolt was used, an updraft could pull the bolt right out of the concrete and ruin your day.

J Bolt

J Bolt

My situation required a reverse installation. I had to put a nut and washer on the J bolt and twist it downward, leaving about 1" of the tip exposed.

J Bolt with Nut and Washer

J Bolt with Nut and Washer

Then I put the J bolt through the hole in the bottom of the post base and put another washer and nut on the J bolt and ratcheted it in place. Basically, the bracket was sandwiched between two nuts and washers with the J bolt.

Post Bracket

Post Bracket

Post Bracket and J Bolt Assembly

Post Bracket and J Bolt Assembly

Some Assembly Required

After assembling the J bolt - post base, I put the Sonotube in place. It required a little bending, but the cardboard tube was flexible. Now I could put the post base assembly.on the post base. It was mounted in place by 2 1/2" #9 (10d) Simpson Strong Tie galvanized structural screws.

The rebar square went on next, surrounding the top of the 4 vertical rebar rods. I wired them in place with rebar wire.

Final Assembly

Final Assembly

Backfill and Mix Well

After the assembly was finished, I made sure the Sonotube was again leveled correctly and backfilled the outside of the hole with dirt it to hold the Sonotube in place.

Finally, I pulled out the orange cement mixer I had purchased from Harbor Freight. It was a priceless piece of equipment used on the deck project last year. While these inexpensive mixers are not commercial quality, they work great for small residential projects. Of course, mixers like this could also be rented from a local home improvement store or concrete could be hand mixed in a wheelbarrow. I mixed up a couple batches of concrete mix and shoveled it into the tube, being careful not to get it all over the post bracket. I used a 2x2 board to poke around the concrete mix in the Sonotube to make sure there were no air pockets as I shoveled in the mix. I filled the tube to overflowing and used a hand trowel to smooth out the top. The very top must be flat under the bracket. I worked mix under the bracket to make sure there would be a flat, solid surface when the concrete dried. As previously mentioned, the outer portion of the top of the footer needed to be rounded to allow water to easily drain off.

Finished Footer

Finished Footer

Settle In

After allowing the concrete to harden for a couple of days, I removed the bottle jacks and was very happy to not hear any cracking or creaking from the deck settling.

Thanks for letting me share and I hope this can help others in the same dilemma. Any questions or comments? Feel free to ask or comment below.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.