I rented an electric jackhammer to break up the concrete patio slab and post footer to remove a deck post. The jackhammer worked great and I was done in less than an hour.
This project is continued from How to Remove a Deck Post in Concrete Slab which shows how I partially cut through the concrete patio slab with a gas concrete saw and drilled a series 1/2 inch holes to weaken the slab for a clean break with the main patio. Also see the sagging deck repair series introduction for the problem description and repair strategy.
How to Remove a Deck Post in Concrete Slab – Part 2: Jackhammer
I hadn’t used a jackhammer before and was looking forward to the challenge. The Hilti TE 3000 weighs 66 lbs and takes an effort to lift and operate. You basically place the chisel on the concrete and guide it by tilting the unit in one direction or the other as it breaks up chunks of concrete. Squeeze the trigger switch and the jackhammer does the rest. The vibration was mild due to the shock absorbing handles. Wear gloves, steel toe boots and safety glasses.
I’ve broken through the patio slab and discovered it was poured as a “cold joint” over the deck post footer:
Notice how the bottom of the 6×6 deck post was set only 2 inches into the concrete post footer!
After removing the deck post, I switched to the flat chisel bit to break the concrete next to the main patio slab. I set the flat chisel behind the wooden dowels (see the above photo) driven into the 1/2 inch holes I’d made with the hammer drill to guide bit. The 1/2 inch weaking holes made a clean break with the main patio slab as I’d hoped. I’m digging out the shallow concrete post footer after breaking it the jackhammer:
Concrete Deck Post Footer Frost Heaving
The concrete deck post footer was only 5 inches thick under the post and was not set a minimum of 12 inches below grade (ground level) to be below the frost line in my area as required by the local Building Department:
A shallow post footer such as this is susceptible to frost heaving where freezing water in the soil lifts footer (because ice expands) and creates a void when the ice thaws. The concrete footer will be resting on unstable soil and sink. The combination of a way too small and shallow post footer with frost heaving may well have caused the corner deck post to sink/subside and the sagging deck.
Note the frost line varies across the country and is deeper in colder climates. Consult your local Building Department for the minimum post footer depth requirements in your area.
Concrete Cleanup and Deck Post Inspection
The wheelbarrow loaded with broken concrete:
I measured how far the 6×6 deck post was set in the concrete patio slab. The bottom section was set just 2 inches in the concrete post footer and was a total of 13-1/2 inches below the patio slab. The good news is the post base has only a minor amount of wood deterioration at the bottom corner after 14 years. I’m surprised I wasn’t able to pull the post out with the 4,600 lb Hi-Lift jack.
View the deck and temporary support post after jackhammering out the old 6×6 corner deck post:
This project is continued in How to Dig a Deck Post Footer.