Building Small deck for timber cubby house on top

[PatDIY_Dad]

Hey 

I am going to build a deck that will be about 200mm off ground level and will be 2.5m x 2.5m

I have a few questions

I want to concrete some hardwood fence posts as the stumps

How deep in the ground should they go in?

I will put in 9 stumps. I will buy minimum quantity of sand and rock mix for concrete from the local nursery 

How many bags of cement would be needed for 9 holes?

Then I will fix 3 long treated pine joists to the stumps. What size would be suitable?

I will do something similar to this video https://youtu.be/QTQeIZT4U-I

[Jewelleryrescue]

Hi @PatDIY_Dad 

That video showed them digging holes approximatly 500mm below ground  height asa  guide if you look at there  auger is has tape lines as depth guages so they go to the same level every time each hole.  A suitable  depth for purpose.

The trick  here is to dig small diameter holes so the timbers go in and less concrete is needed. Larger (deeeper or wider)  the  holes the more concrete needed.

Look at in vesting/borrowing in a small auger, or a post hole shovel for this   task it will help keep hole size smaller.

ps  As a  must do  use H4 treated  pine for this type of footing.

I dont recommend  buying sand and gravel  from the nursery for smaller  jobs  unless you are also doing more  concretng  later on. A nursery will charge  $70 to 80 delivery fee but will deliver sandand  gravel in the same load.

As  for concreting the best  easiest option is to buy premixed   sand and cement bags at bunnings  All you have to do is  use a  wheel barrow is  easiest and mix in water and it is ready to go,  

Some people use a fast set cement for this that sets fast in near 15mins I highly recommend  you dont buy this for your first rodeo as regular sand cement slower  setting allows you more time to position things  correctly if some thing needs fixing.

For a  500mm hole you  will need 2 to 3 bags of sand and cement 20 KG per hole If you have bags  left over get a  refund on the unopened ones

You  want  9  Stumps  so  thats  27 bags. Probably buy 20 bags initailly and see how you go if  bunning quite close to you.

Australian Builders 20kg Sand And Cement Mix Bag I/N: 0760612  $10^.07

https://www.bunnings.com.au/australian-builders-20kg-sand-and-cement-mix-bag_p0760612