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. (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.
Deck Post Footers on Uneven Ground
Eric asked about locating the stand-off post base without a plum bob. I had a similar challenge when I later rebuilt the deck stairs, which required digging new footers for the four 6×6 posts that support the landing. See Build Wood Deck Stair Landing: Concrete Footers and 6×6 Posts for the full write-up.
The post footers have different elevations due to the sloping ground. After digging 18 inch deep footers I needed to locate and mark the center of each footer on the 2×4 concrete forms to embed the anchor bolts. My solution was to drive 1/2 inch x 4 feet long rebar stakes in the footers. The steps are:
- Drive in the 1st rebar stake (left side downhill in the following photo) in the center of the footer by measuring against the wood form. Plumb the stake with the spirit level.
- This stake is the first corner of the rectangle layout of the four post footers.
- Tie the construction string to the stake and run the string out so it’s taunt and parallel to the main deck.
- Set the 2nd stake in the center of the footer against the taunt string and check for plumb.
- [1st rebar stake] — string — [2nd stake] —- string — [main deck]
- Loop the string around the 2nd stake.
- Pull the string to the 3rd footer (lower right in the following photo).
- Have a helper hold the carpenter square on the string at the 2nd stake.
- Move the string left or right until it makes a 90 degree angle with the square.
- Set the stake in the 3rd footer inline with the string.
Drive in the stake and check for plumb.
- Pull the string to the 4th footer (lower left side of photo).
- Hold the square at the 3rd stake and square the to the 4th footer.
- Drive in the 4th stake and check for plumb.
- Pull the string from the 4th rebar stake back to the 1st rebar stake to close the rectangle.
- Double check the string at all corners for square and fine tune as needed.
The simple 2×4 wood forms are held in place by packed moist dirt:
Next, mark the center of the footer on the wood concrete form by referencing the rebar stakes which form a rectangle with 90 degree corners. I used an aluminum yardstick to make the red center marks – recall the marks are not centered on the wood form but to the overall rectangle footer layout per the carpenters string:
Because the deck stair posts are only ~6 feet tall, I used the Simpson Strong Tie ABA66Z Z-Max 6 by 6 Adjustable Post Base instead of the Simpson PBS66HDG Standoff Post Base. Commercial deck builders in my area seem to favor the ABA66Z adjustable base because it requires less precision, although that wasn’t my motivation. The ABA66Z does not include a 1/2 inch anchor bolt, so I bought 1/2 inch x 8 inch long galvanized foundation anchor bolts shaped like an L to better resist pullout. The bolt is set in concrete by referencing the red center marks on the wood form with an aluminum straight edge. The PBS66HDG standoff post base would be set on center the same way:
After the concrete has cured, the ABA66Z installs with a washer and nut. Spin the nut hand-tight on the anchor bolt. Once the post is fastened to the base and final alignment is complete, an open end wrench will fit in the open side of the post base to tighten the nut:
The 6×6 post is fastened to the ABA66Z base with eight (8) SD #10 x 1-1/2 inch screws:
Because the ABA66Z anchor nut was hand tightened only, you can bump or twist the post base with your boot toe or rubber mallet to fine tune the 6×6 post alignment. The anchor nut is then firmly tightened with an open end wrench. The new deck stair landing posts have been notched for the double beams:
The completed deck stairs and landing rebuild:
This project is continued in How to Install a 6×6 Wood Deck Post.
Hope this helps,
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