The big event is here! Today I’ll saw down the old 6×6 wood deck post and cut the concrete patio slab with a gas concrete saw. This project is continued from How to Replace a 6×6 Wood Deck Post – Part 2. Also see the beginning of the project series with How to Repair a Sagging Wood Deck.
How to Remove a Deck Post in Concrete Slab
I used the circular saw to cut around the 6×6 deck post, then sawed a wedge on the far side so it would fall into the backyard like felling a tree. The circular saw couldn’t quite cut completely through the post and I finished the cut with a handsaw while pushing on the post. Success! The deck didn’t fall on me and the temporary support post is holding steady. Note the cable winch is still in place pulling the deck together.
The old 6×6 deck post split when it hit the ground. I’m planning to use it as a landscape border.
Try Pulling the Deck Post from the Concrete Patio Slab
My initial approach was to pull the old 6×6 deck post from the concrete patio slab with a Hi-Lift jack. This would tell me how thick the slab is and how deep I’ll have to dig to reach the old post footer. I drilled a 1/2 inch hole in the 6×6 post stump, installed a 1/2 inch bolt and washers, then wrapped a heavy chain around the bolt:
I bought a Hi-Lift Jack rated for 4,660 lbs. lift capacity and attempted to pull the post from the concrete patio slab.
The post didn’t budge and I bent the 1/2 inch bolt:
I next drilled and set a 3/4 inch steel bolt in the post stump. The bolt didn’t bend nor did the post budge, instead I locked up the jack. Time for Plan B.
Remove a Wood Deck Post with a Concrete Saw
The patio concrete slab must be sawed to make clean straight cuts to avoid damaging the main patio slab. After sawing, I’ll use a jackhammer to break up concrete and remove the deck post.
I tried to rent a concrete chainsaw but none of the tool rental dealers in the Atlanta, GA metro area stocked them, except one store who’s saws were all out for repair. A concrete chain saw would have enabled me to make a straight deep cuts all the way through the patio slab.
Gas Concrete Circular Saw
I rented a 16 inch gas concrete circular saw from Home Depot Tool Rental which is limited to a 5-7/8 inch deep cut (here’s an electric version). Be sure to ask for the water hose connector to keep down the dust. The concrete saw cut the slab like butter. Your pants will get wet from water and sludge. Also be careful to wait for the saw blade to spin down before lifting the saw up and moving to another position because the gyroscopic forces are quite significant.
I made several narrow cuts and broke out the slab like slices of bread. I noticed there was no reinforcing remesh (welded steel wire mesh)in the concrete – this is what happens when the former homeowner’s have work done without filing for a Building Permit.
I sawed out three slices of concrete slab on each side of the patio slab – see the following photo. I would have made more cuts but concrete saw couldn’t get any closer to the 6×6 deck post stump.
Drill Holes to Weaken the Concrete Slab
To weaken the slab for a clean break with the jackhammer, I drilled a series closely spaced 1/2 inch holes with hammer drill. This was slow hard work that took from 5 to 10 minutes to drill each hole with my old drill and a new masonry bit. Next time I’ll rent a more powerful hammer drill from the tool rental store. The thickness of the slab varied from about 6 inches to about 16 inches near the outside edge. The drill vibration changed as I was about to break through the slab and hit dirt. I kept a stream of water on the drill bit to prevent it from overheating and burning up the bit:
I’m halfway done drilling holes. Bird’s eye view looking down from the deck. The temporary support post did great!
Finished drilling the 1/2 inch holes to weaken the slab:
Thinking about ancient stone quarrying methods, I drove wooden dowels in the holes and soaked them with a fine spray from the water hose overnight hoping the wood would swell and crack the patio slab. The dowels fit very tight but it didn’t work – probably because the dowels needed to be larger and/or I needed drive in wooden wedges:
I next rented an electric jackhammer which worked great as I explain in How to Remove a Deck Post in Concrete Slab – Part 2.
Hope this helps,