DIY Deck Build - Advisable?

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2102 posts

Uber Geek

#2635850 15-Jan-2021 09:49

Paul1977:

1. I had looked up the Mitre 10 guide before I started digging which said all holes so be at least 450mm deep - so I did most of mine probably 500mm+. I should have looked at the building code and other guides more carefully (which I did yesterday), because most of the holes actually only need to be 200mm min deep!

Triple read the document!

Holes should always be at least 450mm deep into solid
ground. Anchor piles and braced piles must be 350x350
square or 400mm diameter and 450mm min. into solid
ground. All other piles may be 290mm diameter and
450 mm min. into solid ground.

BlinkyBill

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#2635853 15-Jan-2021 09:51

Thanks for the powerplanter link, it looks good - is it though?

mdooher

Hmm, what to write...
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#2635855 15-Jan-2021 09:58

Paul1977:

mdooher:

200 deep? don't do that, just because it's the minimum doesn't mean it's a good idea. The way I do it is, dig the hole a bit too deep, put a brick or something in the bottom of the hole to stop the post touching the dirt, use quickcrete to set the post in place. then once all the posts are in place and set fill the rest of the hole with "real" concrete. Some might disagree with this but I find the post ends up far more solid this way, that quickcrete seems to have some give in it (they say it is actually stronger than the real concrete...But experience has shown me otherwise

don't worry about the hole being wet, (get out the majority of the water, but the wet hole helps stop the moisture being sucked out of the concrete) you should wet the hole before putting in the concrete anyway

Cheers. Yeah, I would have still done deeper than 200 (it does sound quite shallow) - I'm just trying to see if there was any easy way to save on some costs e.g. 0.6 piles instead of 0.9, or 0.45 (0.9 cut in half) instead of 0.6.

I was looking at this stuff since it doesn't require mixing. It says it cures to 20MPa, but also says not recommended as structural concrete which would imply it's not as strong. Any type of bagged concrete seems quite expensive for the the number of bags you end up needing, is there a more affordable way to do it than bagged concrete?

It was more the sides of the holes starting to collapse rather than the fact the they were wet.

the cheapest way to get concrete is to get half a scoop of builders mix (maybe $20) and a bag of cement. Sure a concrete mixer is the easy way to mix it but if you don't have one you can do small loads in a barrow no problem

if the holes are deep enough don't worry about the sides collapsing a bit just fill with concrete

Matthew

xcon

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#2635857 15-Jan-2021 10:00

BlinkyBill:

Thanks for the powerplanter link, it looks good - is it though?

I find it great with a big corded drill - (i done 50+ holes for decking posts so far)

I've used it to get holes started drilling into clay ,then carved the walls of the holes with the spade

I've drilled holes ~ 450mm deep , then wide then walls with a spade

Paul1977

5042 posts

Uber Geek

#2635873 15-Jan-2021 10:45

itxtme:

Triple read the document!

Holes should always be at least 450mm deep into solid
ground. Anchor piles and braced piles must be 350x350
square or 400mm diameter and 450mm min. into solid
ground. All other piles may be 290mm diameter and
450 mm min. into solid ground.

Yep, Mitre 10 document says all holes should be at least 450mm. But the other NZ guides I've looked at (one was Placemakers), and the NZS3604:2011 all say minimum 200mm (for non-bracing/non-anchor piles).

200mm does sound shallow side though, and I want them deeper than that.

Perhaps the Mitre 10 guides says 450mm because it's just better practice?

Paul1977

5042 posts

Uber Geek

#2635889 15-Jan-2021 11:22

mdooher:

the cheapest way to get concrete is to get half a scoop of builders mix (maybe $20) and a bag of cement. Sure a concrete mixer is the easy way to mix it but if you don't have one you can do small loads in a barrow no problem

if the holes are deep enough don't worry about the sides collapsing a bit just fill with concrete

Thanks, I'll definitely look into that - sounds like it could work out a lot more affordable. Hiring a concrete mixer isn't actually that expensive either - or even buying a small cheap one if it's going to save money over bagged stuff might be worth it.

Paul1977

5042 posts

Uber Geek

#2635890 15-Jan-2021 11:24

The more I read, the more questions I have - but better to ask them now I guess!

If I'm reading NZS3604-2011 correctly, for ordinary piles I don't need to completely fill the hole with concrete - just at least 100mm under the bottom of the post and 100mm min above the bottom of the post (figure 6.2)? But anchor piles should be concreted right to the top of the hole (figure 6.10)? Is this correct?

Tradepub

Free professional, reference and technical white papers (affiliate link).

duckDecoy

896 posts

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#2635892 15-Jan-2021 11:25

chevrolux:

Getting your piles straight is easy. The good builders fill their hole with cement, drop the pile in, and then brace. But I wasn't that confident getting them straight that quickly, so just pegged them all out first (taking my time), and then did all the concrete in one go.

The rapid set concrete bags can be useful here, they go firm quickly enough to allow you to do it by hand

You put your post in and hold it, put some rapid set concrete in, pour in some water, and put your post level onto the post and hold it level and beffore long it stiffens up and you can let it go and put more concrete in. I did 4 posts recently using this method without any pegging out.

duckDecoy

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#2635894 15-Jan-2021 11:28

Grunta47:

Paul1977:

I thought I'd read (possibly years ago) on Geekzone, that the easiest way to do the posts is to attached them to the bearers first and brace the whole thing in place, then concrete the holes.

Does that sound right, or am I misremembering?

Have done this when a group of us built a mates deck and it worked quite well. Deck was only around 300mm off the ground so we set up the bearers, joist and a couple of bits of decking to the level we wanted (just below the sill/step of the sliding door), dug the post holes and ‘hung’ the posts from the bearers and chucked in some concrete.

it was fairly much a measure by eye for everything close to the house but was fairly easy at it was in a corner.

My mates dad used this method and it didn't work well at all, didn't stay level. I assume the bracing slowly sagged under the weight or something.

Bung

6479 posts

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#2635895 15-Jan-2021 11:28

An ordinary pile has to have a minimum footing of 200mm concrete(100 under/100 up side) but that is when you've reached "undisturbed good ground". If you've had a garden that's been dug over you may have to go deeper than 450mm. The footing doesn't have to be right to the top of the hole just as specified for the type of pile.

duckDecoy

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#2635897 15-Jan-2021 11:31

xcon:

If you are digging into clay for your holes i find this handy to get start on the holes, the Power Planter Auger https://powerplanter.co.nz/products/power-planter-324

I use mine on a corded drill

Ive got one of those for the garden and they're great. But you can rent a post hole borer for a day for about $50, which might be more economic.

Paul1977

5042 posts

Uber Geek

#2635898 15-Jan-2021 11:34

Bung: An ordinary pile has to have a minimum footing of 200mm concrete(100 under/100 up side) but that is when you've reached "undisturbed good ground". If you've had a garden that's been dug over you may have to go deeper than 450mm. The footing doesn't have to be right to the top of the hole.

That makes sense. The holes were all pretty firm at the bottom (will have to scrape some mud out once it firms up a bit more from the bottom after the flooding though).

chevrolux

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#2635902 15-Jan-2021 11:39

I just got the green bags of readymix from Bunnings. Bag at a time in the wheelbarrow kept it manageable. Ended up being a 2 bags a hole (more or less, some holes I got a bit carried away on width wise!)

BlinkyBill

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#2635949 15-Jan-2021 11:47

duckDecoy:

xcon:

If you are digging into clay for your holes i find this handy to get start on the holes, the Power Planter Auger https://powerplanter.co.nz/products/power-planter-324

I use mine on a corded drill

Ive got one of those for the garden and they're great. But you can rent a post hole borer for a day for about $50, which might be more economic.

I know this is off topic, but I’ve got about 500 trees and shrubs to plant and this looks ideal. Plus the occasional post hole.

thanks both, I will get one.

Paul1977

5042 posts

Uber Geek

#2635956 15-Jan-2021 11:51

duckDecoy:

Ive got one of those for the garden and they're great. But you can rent a post hole borer for a day for about $50, which might be more economic.

I borrowed a petrol borer from a work mate. 200mm diameter, then squared the holes with a spade.

A day might have been enough for someone fitter, or more experienced - but it wouldn't have nearly been long enough for me. I'm not overly fit, and it was bloody hard going because of the number of large stones that would stop it in it's tracks (and try to dislocate my shoulder in the process). There was a lot of pulling it out of the hole, dislodging stones and trying again (rinse and repeat). By the time I got to the end I had developed a much better technique - but it was still much harder work than I though it would be.

If there hadn't been all the stones it would have been pretty easy though.

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