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Doggo approvedOur back deck needed replacing, especially after part of it gave way under hubby's foot, thankfully he didn't fall through it.
We thought it would just be a matter of replacing the deck but we opened up a can of worms.
Materials
Merbau decking https://www.bunnings.com.au/specrite-90-x-19mm-merbau-pre-oiled-decking-random-lengths-90mm_p0200172
Protectadeck joist protection https://www.bunnings.com.au/protectadeck-45mm-x-50m-flexible-pvc-joist_p0910783
Joist hangers, 50mm climacoat decking screws (no longer sold by Bunnings due to supplier change)
Decking oil https://www.bunnings.com.au/timber-protect-4l-water-based-exterior-decking-oil_p1400470
Deck scrubbing brush https://www.bunnings.com.au/oates-long-handle-deck-scrub-brush_p4460246
Unipro jumbo deck brush https://www.bunnings.com.au/uni-pro-175mm-jumbo-deck-brush_p1662785
Tools
Prybar and hammer to remove
Mitre saw to cut to length
Multifunction tool to notch out posts and decking boards around posts
Drill, Impact driver
Steps
Step 1
We removed as much of the old decking as we could while still leaving a path for us to get up and down the stairs. This revealed every second joist needed replacing as well as most of the bearers. Two posts also needed replacing when we found them to be quite soft around the middle. 
Step 2
We removed sections at time to fix up or replace, I primed and painted the existing good hardwood joists as well as the new hardwood ones we bought from a local timber yard. I also primed and painted the new posts and bearers ready to go in. I'm afraid I didn't take many photos during the process. In reality this whole thing took over 6mths as we found it all quite daunting at first.
We still needed to keep a pathway so we removed the nails holding the deck to the bad joists and threaded the new ones underneath. We also had a temporary fence between posts to prevent dogs and grandkids from falling through the open deck area.
Step 3
With the hardest part finally done, we were able to move onto laying the deck. We had bought the merbau months previously and had laid it out in the weather for a few weeks to remove most of the tannins etc so it didn't run all over the new paintwork. Some lengths were a little bowed so we used ratchet straps to pull lengths straight against deck spacers.
Step 4
I have a new respect for deck layers, my back absolutely ached while laying this down. I had two drills and an impact driver set up, one with a drill bit, one with a countersink bit and the impact driver with a square drive bit in it. Hubby got hit with the flu just after starting and I couldn't just leave it so continued on my own.
Step 5
With the deck now laid, I gave it a good scrub with nappysan, rinsed and then applied 3 coats of Timber Protect Decking oil.
Step 6
Our deck only used less than a litre for 3 coats, so I took the remainder over to our daughter's deck, cleaned it up and it drank over 6 litres with 3 coats, hadn't been done in a long time.
