DIY Deck Build - Advisable?

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94 posts

Master Geek

#2635607 14-Jan-2021 15:41

neb:

It would help to explain the reason for the grooves-down placing: The grooves are meant to help airflow to stop moisture buildup. Conversely, grooves-up will allow debris and later moss and mould to build up in the grooves. Once you know the reason it's obvious, but without that I can see how people would install them "with the grippy side up".

Sorry, but I dont think that is totally correct. One side smooth and the other side grippy is really designed for personal preference. Ive heard this discussion many times and every home handyman/builder I know has their own opinion. Plus, when you purchase standard decking the poorer quality (knots, etc) is usually on the smooth side.

Have just started building a deck at the moment with 150 x 40mm pine decktred (ends up being 140 x 32mm dressed) it has grooves on both sides. One is the grippy tread while the other is the boardwalk style (about 4 grooves across the width).

If you purchase standard boardwalk decktred then this is boardwalk one side and flat on the other. The boardwalk tred sits up and as noted above has far less imperfections than the flat side.

Paul1977

5039 posts

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#2635609 14-Jan-2021 15:43

Off topic - but when a family member had some decking built at a commercial property that required a wheelchair ramp as part of it, the council made them take up the boards on the ramp and reinstall them groove side up because the inspector was insistent it was required for better grip.

chevrolux

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#2635615 14-Jan-2021 15:51

Regardless of grip, the grooves are just ugly! Who would want to look at them!

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.

One consideration I had for design was I wanted to dig the least amount of post holes. So went 32mm thick decking, 450mm joist spacing (140x45 joists), and 140x90 bearers. And that let me push the pile spacing, and joist span (across the bearers) to the maximum allowed in the guidelines. After building it, its dam strong and there is absolutely zero flex anywhere. I reckon it could be leaned out even further, but wanted to try and stick to the rules.

Paul1977

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#2635618 14-Jan-2021 15:59

chevrolux:

One consideration I had for design was I wanted to dig the least amount of post holes. So went 32mm thick decking, 450mm joist spacing (140x45 joists), and 140x90 bearers. And that let me push the pile spacing, and joist span (across the bearers) to the maximum allowed in the guidelines. After building it, its dam strong and there is absolutely zero flex anywhere. I reckon it could be leaned out even further, but wanted to try and stick to the rules.

We have less ground clearance to work with, so have to go with smaller bears and joists. Digging holes is good exercise.

mdf

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#2635652 14-Jan-2021 17:53

Absolutely can be DIYed. Most important thing (IME) is allowing ***way*** more time than you think it will take.

neb

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#2635660 14-Jan-2021 18:27

Grunta47:
Sorry, but I dont think that is totally correct. One side smooth and the other side grippy is really designed for personal preference. Ive heard this discussion many times and every home handyman/builder I know has their own opinion. Plus, when you purchase standard decking the poorer quality (knots, etc) is usually on the smooth side.

True, I've seen debate going in both directions, but the grooves-down one was the only one that had any supporting arguments. OTOH I can't see why milling grooves into the timber would help with airflow or drying, and it'd add to the cost of making the stuff, so it may be an argument that's pulled out of thin air, or possibly less well-lit places. In addition if it was that obvious that grooves-down is better then suppliers would have "MUST BE INSTALLED GROOVES DOWN OR YOUR WARRANTY IS VOID" everywhere they discuss their product. Anyone want to phone CHH and see what they say?

For a smaller manufacturer, Kiwi Lumber says grooves up.

Bung

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#2635673 14-Jan-2021 19:26

It's mentioned in D1 Access Routes that grooves up meets slip resistance requirements if grooves are at right angles to direction of movement. Apart from that I think it is an appearance thing. Some timber mill probably started off using it to hide timber defects. I've got some old 1980s Kwila that has very fine grooving compared to current samples. That didn't help the pine joists it was nailed to.

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Grunta47

94 posts

Master Geek

#2635676 14-Jan-2021 19:47

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.

Brunzy

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#2635680 14-Jan-2021 20:01

Do it!
A good level and a few string lines are your best friend, for setting it out.

Batman

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#2635698 14-Jan-2021 21:17

Paul1977:

The builder who was going to do my deck (with me as helper to keep costs down) has changed jobs and now isn't available. I've been looking at various guides, and it all looks do-able (in theory), but is this something I should attempt myself having never done one before?

Most of the tools that I don't have myself I'm able to borrow, but I haven't tackled anything like this before so am a little uncertain if it's a good idea.

My neighbour built his deck within a week. he's no builder.

darylblake

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#2635704 14-Jan-2021 21:24

Good on you.

Challenge yourself and do it yourself. You will feel a sense of achievement.

My advice.

1) Plan it.
2) Take your time, especially with the foundations, joists and bearers.
3) If you have difficult terrain to work with, then maybe get some help... but if its basic and flat you should be good to go.

xcon

147 posts

Master Geek

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#2635741 15-Jan-2021 07:39

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

Paul1977

5039 posts

Uber Geek

#2635776 15-Jan-2021 09:05

The builder had already planned post placement, and I have been slowly getting through digging the holes in my spare time and just finished in the weekend. But I already have a couple of issues:

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! Presumably having them deeper will just make the deck sturdier (and the exercise was good for me), but having them all this deep will also cost significantly more in the cost of the posts/concrete. I don't know whether I should backfill them because I'm not sure how to sufficiently compact any earth put back into the bottom of the holes? We're talking about 27 holes/piles. Can they be easily backfilled and sufficiently compacted by hand, or at this point am I best to just suck it up and get longer posts?

2. I got home last night and the back neighbour had been overwatering his garden and it flooded into our yard and had completely filled 5 or 6 of the holes. I scooped out as much as I could, but the sides of some of the holes have started collapse in on themselves from being submerged in water for several hours and the bottom of the holes are a soggy mess. I have no idea what (if anything) I need to do about the effected holes?

mdooher

Hmm, what to write...
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#2635789 15-Jan-2021 09:26

Paul1977:

The builder had already planned post placement, and I have been slowly getting through digging the holes in my spare time and just finished in the weekend. But I already have a couple of issues:

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! Presumably having them deeper will just make the deck sturdier (and the exercise was good for me), but having them all this deep will also cost significantly more in the cost of the posts/concrete. I don't know whether I should backfill them because I'm not sure how to sufficiently compact any earth put back into the bottom of the holes? We're talking about 27 holes/piles. Can they be easily backfilled and sufficiently compacted by hand, or at this point am I best to just suck it up and get longer posts?

2. I got home last night and the back neighbour had been overwatering his garden and it flooded into our yard and had completely filled 5 or 6 of the holes. I scooped out as much as I could, but the sides of some of the holes have started collapse in on themselves from being submerged in water for several hours and the bottom of the holes are a soggy mess. I have no idea what (if anything) I need to do about the effected holes?

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

Matthew

Paul1977

5039 posts

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#2635847 15-Jan-2021 09:48

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.

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