Deck Piles Footing

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meekzone

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#270010 19-Apr-2020 15:29

When placing decking piles into the ground, do you put 100mm concrete underneath? Or a brick? Or rawdog it against bare soil?

BRANZ magazine says 100mm concrete, mitre10 video shows brick underneath, and a builder mate of mine says naked and afraid. What says your collective wisdom?

Edit: spacing

SATTV

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#2465465 19-Apr-2020 15:52

I always do the 100mm concrete personally as that was what I was taught 30 years or so ago.

There are other systems like screw piles these days that are faster and probably better.

The other system I like is the expanding foam in place of concrete, way faster just as solid.

John

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DarthKermit

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#2465473 19-Apr-2020 16:09

It's good practice to have your piles suspended ~ 100 mm above the bottom of the hole.

Join your piles together onto the bearer timber.

One useful way to get the bearer level is to use one or more car jacks to precisely level it.

jjnz1

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#2465483 19-Apr-2020 16:16

SATTV:
I always do the 100mm concrete personally as that was what I was taught 30 years or so ago.

There are other systems like screw piles these days that are faster and probably better.

The other system I like is the expanding foam in place of concrete, way faster just as solid.

John

I agree - 100mm concrete. Very easy to do as your piles will be braced anyway, just before you screw off the brace (easy than nail btw) lift it up 100mm.

neb

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#2465785 20-Apr-2020 02:02

SATTV:
I always do the 100mm concrete personally as that was what I was taught 30 years or so ago.

I would assume a concrete or similar shoe has two advantages over a brick/nothing, firstly it spreads the load from the pile out over a much larger area so instead of x kg per unit area you might have x/2 or x/3 kg per unit area, the other thing is that even an H4 or H5 pile doesn't mean "magically immune to rot", it just means it's more resistant to it than lower grades of treated timber, so encasing it in concrete will help with rot resistance.

And then you get rot at the point where it meets the concrete, as one of our house piles did. Not sure what happened there but it was rotted completely through just above the encasing concrete.

Bung

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#2465790 20-Apr-2020 05:18

It must be load support related as 3604 gives increasing size with number of storeys. An ordinary pile needs 100mm under it and minimum of 100mm around it. Anchor and braced piles need more depth of concrete surrounding them but none seem to require concrete filling the full height of hole. The concrete under the pile can be a precast pad or you can get plastic feet for piles that hold them 100mm off bottom of hole but take weight before concrete sets.

meekzone

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#2466128 20-Apr-2020 13:05

Thanks guys. 100mm it is. Now about that level 3...

sampler

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#2466187 20-Apr-2020 14:40

How about these plastic fancy footing things ?? -> https://constructionplastics.co.nz/products/space-it-pile-pad

KennyM

221 posts

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#2466325 20-Apr-2020 15:18

Note - NOT a builder.

The deck I built at our last house we assembled the bearer's and attached the piles, then hung it 100mm above the bottom of the holes as mentioned above.

I found it to be a really easy way of doing it, much easier then trying to cut off all the piles at the correct height afterwards. (a builder doing it every day would do it fine, im not a builder)

The last deck I helped my mate do, we put cobbles on the ground (mostly grass) and put the joists straight onto them with a timber packer (cut to suit) between the cobble and joist. his deck wasnt high enough for a bearer, it was also over 50square meters - and not a single hole was dug.

If i was doing another deck that wasnt too high off the ground, I would do it the cobble way again. I just messaged him to ask if he had noticed any movement in it, he said no - but only thing he could think of would be a better laser level next time.

This was the only photo I found, Some are multiple cobbles.

DarthKermit

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#2466352 20-Apr-2020 15:49

KennyM:

Note - NOT a builder.

The deck I built at our last house we assembled the bearer's and attached the piles, then hung it 100mm above the bottom of the holes as mentioned above.

I found it to be a really easy way of doing it, much easier then trying to cut off all the piles at the correct height afterwards. (a builder doing it every day would do it fine, im not a builder)

The last deck I helped my mate do, we put cobbles on the ground (mostly grass) and put the joists straight onto them with a timber packer (cut to suit) between the cobble and joist. his deck wasnt high enough for a bearer, it was also over 50square meters - and not a single hole was dug.

If i was doing another deck that wasnt too high off the ground, I would do it the cobble way again. I just messaged him to ask if he had noticed any movement in it, he said no - but only thing he could think of would be a better laser level next time.

This was the only photo I found, Some are multiple cobbles.

Why did you cut holes into the existing concrete rather than have the piles simply sitting on top of the concrete pad?

KennyM

221 posts

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#2466388 20-Apr-2020 16:18

DarthKermit:

KennyM:

Note - NOT a builder.

The deck I built at our last house we assembled the bearer's and attached the piles, then hung it 100mm above the bottom of the holes as mentioned above.

I found it to be a really easy way of doing it, much easier then trying to cut off all the piles at the correct height afterwards. (a builder doing it every day would do it fine, im not a builder)

The last deck I helped my mate do, we put cobbles on the ground (mostly grass) and put the joists straight onto them with a timber packer (cut to suit) between the cobble and joist. his deck wasnt high enough for a bearer, it was also over 50square meters - and not a single hole was dug.

If i was doing another deck that wasnt too high off the ground, I would do it the cobble way again. I just messaged him to ask if he had noticed any movement in it, he said no - but only thing he could think of would be a better laser level next time.

This was the only photo I found, Some are multiple cobbles.

Why did you cut holes into the existing concrete rather than have the piles simply sitting on top of the concrete pad?

Consistancy, out of camera they are all into dirt, if I was to do it again I would sit any above concrete on the concrete - most likely with a bracket.

mdf

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#2466401 20-Apr-2020 16:31

Cobbles are a good solution for the right type of soil. Don't use this approach on anything soft or likely to shift.

My usual approach is to hang the pile over the hole, then backfill with concrete. If you have a big (>125mm depth of cut) circular saw and a rotary laser level, I can totally see it is easier and faster to chuck them in any which way and trim to level. But if you don't, easier to level a bearer than cut piles level.

meekzone

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#2471075 25-Apr-2020 14:20

What's the best way to suspend the posts? Does all the concrete need to go in at the same time for best strength? Or can I pour 100mm layer, let it dry, put the posts on top, then backfill with more concrete?

The reason is I can mark the final height of the posts with level and cut it with the mitre saw and get nice straight cuts, rather than my skill-less saw. But obviously, it that affects the strength of concrete, I'll have to have the posts hanging 100mm instead.