I’ll make a wood form and pour the concrete footer with a rebar reinforcing cage to replace a 6×6 post fix a sagging wood deck. This project is continued from How to Dig a Deck Post Footer.
How to Pour a Concrete Deck Post Footer
I bought 28 bags of QUIKRETE Concrete Mix (No. 1101) in 80 lb bags at the home improvement store and had it delivered on a pallet. QUICKRETE No. 1101 has a 4,000 PSI average compressive strength which exceeds the minimum 3,000 PSI required by my local deck code. I also rented a 3 bag electric mixer from Home Depot Tool Rental but here’s an inexpensive one if you wanted to have your own and not have to rent. (The fun part was moving the bags of cement from the driveway to the basement patio.) Note the concrete edger and float tools on the cement bags:
Deck Post Footer Drawing
Recall the design I made for the new deck post footer with a rebar cage and Simpson Strong-Tie PBS Standoff Post Base is:
And overhead view:
I omitted the two horizontal rebars that I had planned to drill and epoxy into the main patio slab because the ridges made by the hammer drill will provide a mechanical bond between the new footer and existing patio slab.
Make a Wood Concrete Form
The deck post concrete footer will poured to the level of the basement patio slab. I made a concrete form out of scrap lumber and plywood. The form was fastened to the patio slab with Tapcon concrete screws and round steel stakes with holes for screws driven in the ground. Take care to ensure the top of the wood form is level and even with the patio. Afterwards, I coated the inside of the form with motor oil to prevent the concrete from sticking:
Due the ragged edges in the patio slab where I had drilled 1/2 inch weakening holes before removing the old deck post with the jackhammer that will provide a mechanical connection, I choose not to install the horizontal rebar in the side of the patio slab deeming it unnecessary. I did coat the exposed surfaces of the patio slab with QUIKRETE Concrete Bonding Adhesive:
I mixed three 80 lb. bags of cement in the mix according to the manufacturer’s instructions and made my first pour. Keep the mixer running so the concrete flows out. The mixer tilts forward to rest on the lower frame for pouring… very convenient!
I set the rebar cage in the footer excavation after the first concrete pour so it sat 3 inches above the soil, then continued mixing and pouring. I worked a 2×4 up and down to consolidate the concrete (remove large voids) after each 3 bag pour. Some water will rise to the surface as you work the concrete:
The How to Build Deck Footings with QUIKRETE is an excellent overview:
It took less about 90 minutes to mix and pour the concrete.
When the concrete is slightly higher than the wood forms, use a 2×4 screed board to level the surface and remove the excess. Work the screed board back & forth in a sawing motion while moving sideways:
How to Install a Simpson Strong-Tie Standoff Post Base
The new 6×6 deck post will be anchored in the footer with a Simpson Strong-Tie PBS66HDG Standoff Post Base and I need locate the center of the post relative to the deck by:
- Measure where the center of the new 6×6 post will be at the corner deck beams.
The actual dimensions of a 6×6 post are 5-1/2 x 5-1/2 inches. Use a carpenter’s square to mark two lines 2-3/4 inches from the deck corner to find the center of the post at the beams.
- Set a screw in the bottom of deck joist where the post center is marked.
- Tied a plumb bob line around the screw.
The yellow arrow points to the screw where the plumb bob is tied:
The plumb bob points to where the center of the new 6×6 deck post and Simpson Strong-Tie PBS66HDG Standoff Post Base will be set:
To install the Simpson Strong-Tie standoff post base in the wet concrete:
- Measure and mark the center of the standoff post base.
Note the red X in the following photo.
- I pushed the post base in the concrete at an angle and worked it in to consolidate the concrete around the base.
The PBS66HDG has a looped bottom and I was concerned about creating a void if I just shoved it straight down in the concrete.
- Checked the standoff post base is centered under the plumb bob.
- Used a spirit level to check the base is level.
I floated the concrete to smooth it, gave it a brush finish with a broom to match the patio for a non-slip surface and edged it when it had stiffen enough for the concrete edger. I covered it with a heavy cotton drop cloth (didn’t have burlap laying around) and kept it moist for 5 days to cure with the wood forms in place. This photo was taken the next morning:
View of the new deck concrete footer looking down from the deck. Couple of observations:
- The old post was 3 to 4 inches off center towards the corner.
The reason why the deck was sagging was due to post/footer movement and sinking. The new post center will be centered below the deck.
- The right side of the basement patio slab was not poured square and angles inward. A cosmetic issue.
This project is continued in How to Install a 6×6 Wood Deck Post.
Hope this helps,