# Forum Home Renovation Decking  Small deck over concrete slab, minimum batten size recommendation needed

## simopimo

I had a 32 m2 deck built last year - spotted gum boards, treated pine bearers and joists.  Following a recent pergola knock down/rebuild, I've decided to extend the deck for the bbq to sit on.  I was originally planning to use pavers for this step down/extension, so I poured a slab, 2.6m x 1.2m - it's only a small area.  *The intention is to have it sitting about 10-15cm lower than the current deck so you can "step down" onto it*, and the bbq will also sit on it.  The builder extended the roof of the new pergola so this area is under an awning.  So weathering won't be a major issue. 
Today I decided that I would deck it instead of paving it, as it would be much better from an aesthetic point of view, and I have enough decking boards left over from the main job.  The slab comes up to ground level, but I've set up the fall so it drains back into the yard.  The boards are 90mm (86mm actually) x 19mm spotted gum. 
I was planning to use H3 treated pine for the battens, dynabolted into the concrete, sitting on top of 1mm packers.  I was hoping to be able to use 25mm thick treated pine but the local hardware stores (both Bunnings and Masters) recommended going with 35mm minimum but couldn't really tell me why.  Maybe it was just because that's what they had to sell, I don't know. 
The boards will run width ways as that will match the existing deck's profile - eg. over the 2.6 x 1.2 m, the boards will be 1.2m. 
So my questions are:  Because I want this area to be as low to the ground as possible, so that it's a useful step from the main deck (which is also close to the ground), could I get away with 25mm battens on 1mm packers for water flow, or would I need thicker battens and packers?  If so, what's the minimum recommended?  Has anyone used less than 35mm battens on top of concrete?It seems that decking screws are 50mm minimum, so am I screwed here (pardon the pun).  My existing deck was built using Razrdeck 50mm screws from Scrooz with torx drive.  The builder liked their screws.  But they're only 50mm or longer, so if I go below a 35mm batten, I'm stuffed.  Any suggestions here (35mm batten, 19mm board, maybe thicker packers like 3mm, or 40mm decking screws)?Is dynabolting and countersinking the battens into the concrete the standard way to do this (maybe with a bit of construction adhesive on the packers at the same time)?  Or is there an easier/better option?  It's not as if the area is taking a lot of weight - absolute max 2 people at any one time...What gap should there be between each board?  I'm guessing about 3mm (like my existing deck, for consistency's sake?)  What do you use to keep the gap when setting the boards in place, bearing in mind that spotted gum is often slightly bent/twisted?  The builder used some slivers of wood when building the original deck but as a home handyman I don't have those so I was going to use packers for that.  
I have set the fall so the water will drain away from the deck and into the garden/yard.  So no worries there. Suggestions appreciated.  I might knock up a picture if it doesn't make sense...

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## shauck

What is the exact height difference at the deck edge to concrete step down? Is there a reason you want a step down and not same level or even a step up instead?

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## simopimo

Hopefully this illustrates it a little better. There is 15cm height between the deck and slab, in the middle. It is higher at the bbq end so that water runs off into the yard. 
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## simopimo

... And the reason I want a step down is because the awning is fairly low... Lower than the pergola ceiling so it makes a nice logical step down into the yard. My kids are giants and they'd bash their heads (Along with me). 
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## shauck

I'm assuming you are only decking the small concreted area? I can't see how to deal with the height other than to remove the concrete and maybe even a bit of dirt but then you have the problem of the ground around the bbq area being lower than the backyard unless you remove dirt from around the area, right back into the garden or a short retaining wall/step height and drainage. Could look good the length of the whole deck. Then you won't have material restrictions and you can build it like any regular low deck.

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## robjer

hi  
i'm building a 6mx6m deck over a concrete courtyard with the top of joists at 14cm 
the concrete has a slight fall off that means joists are 140mm further off the concrete at one corner compared to the shallow corner 
i've used four different sized galv steel brackets to hold up the joists at the correct height - in place of bearers 
i bought two sizes of L brackets and some post supports from post support aisle in Bunnings and had another size made up by local steel fabricators  
dynabolted to concrete with M12 bolts fastening the joists to the brackets - you can see some of the brackets in this pic   
cheers
Jeremy   

> I'm assuming you are only decking the small concreted area? I can't see how to deal with the height other than to remove the concrete and maybe even a bit of dirt but then you have the problem of the ground around the bbq area being lower than the backyard unless you remove dirt from around the area, right back into the garden or a short retaining wall/step height and drainage. Could look good the length of the whole deck. Then you won't have material restrictions and you can build it like any regular low deck.

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## simopimo

> I'm assuming you are only decking the small concreted area? I can't see how to deal with the height other than to remove the concrete and maybe even a bit of dirt but then you have the problem of the ground around the bbq area being lower than the backyard unless you remove dirt from around the area, right back into the garden or a short retaining wall/step height and drainage. Could look good the length of the whole deck. Then you won't have material restrictions and you can build it like any regular low deck.

  Thanks for the advice shauck.  Yes, only the small concreted area.  I think I'll put up with the height issue because at least it keeps the deck off the ground.  My yard doesn't get full sun in the cooler months, and the existing deck is already quite low anyway.  I like the idea of going right across the yard, however I didn't want to eat into any more yard space so I will keep it restricted to the concrete area for now.  I guess I was hoping to keep the new deck as low as possible, but keep it on the concrete for drainage purposes, which is why I wanted to get as thin joists/battens as possible (like 25mm).  
If I used 25mm joists/battens, this would mean that the deck would only rise 44mm off the concrete (allowing 19mm for the boards), and I'd pack the battens to keep them off the concrete and level.   The concrete has been specifically set to drain water into the yard so I'd simply pack the battens to keep the deck level.  Downside to 25mm battens is that decking screws are generally 50mm, and I guess that's for a reason. So I'd be hitting the concrete when screwing in the boards.  Whereas if I went with standard 35mm H3 battens, the screw length would be OK but the deck would rise about 54mm off the concrete.  Not a showstopper, more of a "nice to have" since a 10cm step is pretty small.  On the plus side though, I have relatives that aren't too mobile so having little steps can be a good thing so they can step onto the little deck and then into the yard.

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## simopimo

Thanks for the response Jeremy.  Pretty similar to what I'm doing.  I was going to skip the brackets though since I only have a 2.5 m2 area to do (and I'll use packers to get the battens/joists off the concrete), but other than that, much the same approach.  Good to hear that I'm sort of on the right track... 
Thanks again, good luck with your deck.

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## Oldsaltoz

I would avoid packers made of anything that will suffer when wet, steel will rust, timber will rot, however the recycld plastic made to look like timber is perfect. 
Good luck.   :Smilie:

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## simopimo

> I would avoid packers made of anything that will suffer when wet, steel will rust, timber will rot, however the recycld plastic made to look like timber is perfect. 
> Good luck.

  Thanks for the advice oldsaltoz. I have a couple of boxes of Macsim plastic packers for precisely that reason.  All good! They won't be visible from above so the colour should be fine.  Cheers! 
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## shauck

I wasn't thinking of your bbq deck being as long as your existing deck, just the cut out/lowering of the ground level. You can take care of the drainage all the way along the low retaining wall, resurfacing the cutout with whatever pleases and gives you reasonable clearance for your bbq deck as well as adding some interest to the landscaping. I can't imagine 25mm battens cutting it really. Not seen treated pine in that dimension. I'm also wondering at what height does a step turn from a step to a trip hazard, anyone? Basically, there are so many cons to this which is why, if it was me, I'd be digging that cutout and putting in drainage and short wall or just go with paving which would be my preference.

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## simopimo

Thanks shauck, will certainly consider that. The advantage of the low step is that it's good for the less mobile elderly members of the family. It's not a thoroughfare so it won't be much of a trip hazard,  but I see where you're going with the advice.  Thanks for your diagram. 
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## shauck

No worries. Just a suggestion. You could still have your small step and have full thickness/suitable materials this way. Ok, enough pushing  :Biggrin:

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## simopimo

Quick final question - since the concrete is unmovable, could I use fencing grade H3 treated pine 25mm for the battens, if they're sitting on packers to keep them off the concrete?

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## simopimo

Had a slight snag on the weekend.  Whilst bolting down the battens, I drilled a lovely tidy hole in the stormwater pipe under the slab.  And of course, it happens to be a charged line so water spewed everywhere, and I had poured the concrete slab only a couple of weeks earlier!!! 
All fixed now.  It seems that ever Saturday is a trip to Masters or Bunnings to gather supplies for the weekend project.  Unfortunately, Sunday is usually a trip to the same place to collect repair supplies!!!! Live and learn.   
That's the price you pay for drilling holes in concrete at 10.30 on a Saturday night.

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## simopimo

Finally finished it.  Thanks to everyone for their advice. 
I was able to re-use some of the spotted gum from my existing deck which had to be removed when extending the outside bathroom.  Saved cash that way, and it meant that good spotted gum wasn't going to waste. 
The main challenges were:  Dealing with the sloping concrete surfaceDownpipe/drain issues (and the multiple repairs that ensued)Warped/non-straight boards.  But reading a few of the posts here certainly helped with that.Re-using existing boards meant that the screw holes didn't all line up, but after the Spa 'n Deck it has toned the screw heads down a little anyway 
I used plastic window packers, lots of them, to get the joists level, and screwed the boards into the concrete through the packers by using Tapcons and dynabolts, about 3 or 4 per joist.  Packers every 20cm or so along the joists, glued to the concrete and the joists.  I used H3 treated pine 90 x 21mm decking boards as joists - seems odd I know, but I painted them before installing them, there's plenty of air flow between the concrete and the joists, and the area gets sun during the day.  The use of those boards also keeps the deck as low as possible so as to not become a trip hazard. 
Coated it last night with the old trusty Spa 'N Deck in Sedona/Walnut, 3 coats, to match the existing deck built last year.  Not bad for an IT nerd eh!!! 
Ugly corner of the yard prior to concrete   
This shot was taken after the slab was poured in 2 phases by hand.  I actually added a small section onto the left after this as it wasn't large enough for SWMBO.   
Frame complete, working during the night so I can do my day job...Wow, this is tough on your back if you're not used to it.    
More of the frame showing the 6 joists/battens.  I learnt that the joists/supports are the hardest part.  Screwing in the boards is pretty easy really (and sort of fun too)...   
Boards almost done.  Using 40mm stainless Razrdeck screws from scrooz.  I was given a DeWalt 14.4v hammer/combo drill and separate Impact driver as a present this year and geez did they come in handy.  Got a process down pat and it went pretty well.  Only wrecked the heads of 3 screws out of about 260.   
Almost done, final check with BBQ in place to ensure all fits well, prior to treatment of the boards   
3 coats of Spa 'N Deck Walnut complete. Gosh the existing deck needs a good clean (again!)   
Overall pic prior to tidying up.  My outdoor room is complete.  At least until SWMBO finds something else for me to do, like landscaping or something similar.

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## robjer

nice job - could see your vision once it was all done 
matches well 
had to laugh when i saw those flood lights - $30 from Bunnies?  
ii got the same ones to work after sun-down during winter on my 6x6 deck which is not close to being finished..

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## simopimo

Thanks robjer. 
The floodlights are pretty much what you said - from Masters instead, but much the same.  They are crap. As are all cheapie floodlights in my opinion now.  Have been through 2 sets of them already, gave up returning them and now only one of them is working. I got sick of the glass shattering so I run them without glass covers now... 
You've got an excuse for yours being slow - it's 36 squares!!!  Mine was about 2.6 squares and it still took a couple of weekends...

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## shauck

Looks great. BBQ weather just around the corner.

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## simopimo

> Looks great. BBQ weather just around the corner.

  Thanks shauck. I am definitely planning to implement some of the ideas you provided to make the surrounding area more interesting. 
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## shauck

Coolio. Post some pics.

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