Help with decking supports

[paulie75]

Hi all,

Newbie post alert!!!
I'm not too sure if this is the right section but I shall fire away and seek your advice. My query is loosely woodworking related, more specifically to do with deck construction. The timber elements I am ok with although there is a lot of variation and opinions as to what is regarded the correct way to propagate. American, Australian, and European techniques are all different. While some seem content to simply place on paving slabs, I would like to build mine to last.

There are many schools of thought on the best way to suspend a deck, and the best way to sink the posts in the ground. I am resolved in my framework and how it will be supported. From what i gather when setting posts in cement the main priority ( apart from being level) is to ensure that they will not sit in standing water. So from this I have decided that a 12"x12" ring of cement around the post will adequately support it. (4x4 post) with the aforementioned post in the middle. I also understand that the general accepted ratio of above ground to below ground is 25% . ie: 4' post = 1' underground. To prevent water build up at the bottom of the post hole with pea shingle , about 6 inches to create a soakaway. So far , so good?

After that incredibly long winded preamble , my question is , would it make sense to precast the concrete supports? I want to make them a decorative feature, so I was thinking of building a shuttering box out of a laminate of 18mm ply and thick plastic sheeting. Each "cell" would be 1 cubic foot with a plastic lined 4x4 in the middle of the form, pea shingle in the bottom so that it could mate to the pea shingle soakaway in the hole .The ply box would be 4' x 5' to make 20 supports for 3' posts.I feel that this would create consistency in the supports and would save time in the deck construction.

~In your opinion would this be a feasible option or am I trying to re-invent the wheel. Please ask for clarification if I have not been concise enough. Thanks in advance for your suggestions and advice.

 

[kostello]

Have a quick look here for some inspiration......

Fivedegreepiers.co.UK

 

[chippy1970]

On most decks I've done and even on my workshop I lay concrete gravel boards on sharp sand and cement. Then lay your joists across those with dpc in between. You get a nice solid deck then. Gravel boards are good because they're reinforced unlike paving slabs.

 

[paulie75]

@kostello- thanks for the link, looks a little advanced , I'm thinking just square atm. Are you suggesting that it would be better to affix the post to the top of the pier rather than encasing them and sinking them?

@chippy1970 - I had thought of the gravel boards, but I need to suspend the deck as my garden slopes. With this in mind i thought to make the concrete surrounds sit proud of the ground and weedsheet as a feature. I will be using 2"x 6" for the frame with the joists 600mm on centre with supporting posts every 1200mm.

 

[kostello]

If the post can't stay wet it won't rot........


There are several proprietary post supports


http://www.screwfix.com/p/sabrefix-stan ... base/85498


Search for post stand off

 

[paulie75]

Thankyou for that link, that would work very well , so theoretically I could still cast the blocks as I originally envisaged and insert the sabrefix into the precast block? Or cast the sabrefixed post in the block? Then all I have to do is drop the blocks in the dug holes and backfill with compacted earth. I'm sorry to harp on but the words of my father still echo in my head to this day. "preparation preparation preparation. if you're doing a repetitive task break it down into sections because if you can save even 30 seconds per repetition blah blah blah". So the thought was cast all blocks, then bore holes as concrete is curing, then insert blocks, instead of doing each post one by one.

 

[Chrispy]

20 blocks each 1ft x 1ft x 1ft = 20 cubic feet of concrete to mix and pour have you thought this through? thats one heck of a mould to make and weight to support.

 

[paulie75]

1 cubic foot was an arbitrary figure, if they were to be cast 8" square by 1' high would they be strong enough ? I was thinking of a way to ensure consistency, maybe just overthinking a situation. In my head it sounded good , on paper it looks good, I just wanted some feedback. Maybe it would be quicker to fill the holes with postcrete one by one. the weight will be about 60kgs per block. maybe I could cast them in boxes of 3x2.

 

[Chrispy]

I thought the normal way to do this was dig hole down to firm base and fill with concrete either with post in or on the said mix.

saves making shuttering moving heavy blocks tamping ground etc. seems to solve a lot of problems that you are making for your self.

 

[paulie75]

That's correct Chrispy. I think I needed someone to tell me that. In hindsight its like NASA spending umpteen millions on developing a pen that would work in zero gravity, when the russians just used a pencil. I suppose i could build forms above ground level in order to achieve the exposed top as a feature. Feedback appreciated.

 

[Dusty]

Evening all , Here is a couple of shots of a decking job done about 5 years ago , still going strong as had to extend it . The posts that would be hidden were sat on blocks that were bedded down and the corners that would show after cladding in were concreted in about 600 down . .

If the posts are treated then they will last a good time in the ground but I always retreat them with a good quality preservative too .

Hope this helps , Sam

 

[slimshady]

My decking is built on 3"-sq green oak joists from a local sawmill. These were layed on engineering bricks on top of some gravel boards and Concrete H posts (well they were lying in almost the right place). But my garden is almost flat; yours has an unknown slope, slight or very severe.?

i did proffer on another forum that the guy used railway sleepers cast in concrete 18"-sq to counter his slope of 36" over 16-ft. This was based on nothing other than 'belt+braces' and back-of-envelope thinking.
In the end he used a big earth auger to drill 12" holes 3-ft deep about 8-ft apart and when concrete dried used a laser to fix a datum. These posts were then sawn level and connected with treated 8"x2" in a grid like the link
http://www.thetopdeck.co.uk/decking_on_sloping_garden_belvedere_kent.htm .
When finished it was decked with Ipe. Hope this gives you food for thought.

Alex.

 

[stevebuk]

i got about 2 cube worth of opepe wood if your interested in buying any, really good stuff and will last a lifetime, they make piers from it..