# Forum Home Renovation Decking  Another Low Deck over Concrete thread - DIY!

## bluemetal77

Hi Guys! Been reading up on these forums for some great advice and examples - Finally getting around to do my decking job. DIY! 
I have gotten quite a few answers but as with any job, mine has some specifics too, so i'll put em down here for you guys to comment. 
1) My decking area is on a concrete slab 4.2m x4.4m (see pic) with house brick on 2 sides. The curved area you see at the end of the area is reserved for some landscaping
2) The concrete only sits 80mm below the sliding doors where it touches the house wall .. so not a lot to play with .. and falls towards the turf (going to a max of 120mm)
3) The only treated pine joist size i could find at bunnings was 35mm x 45mm .. do you think that will work?
4) Thinking of putting hardwood (not decided which one) so that will had another 20mm to 45 .. so 65mm
5) Ive read up that people put plastic packers/wedges to raise the deck and make it level, i'm thinking of NOT making it level and let it follow the fall of the concrete slab (see pic)..
6) Not saying i will not raise the joist from the slab for air/water flow, i will, but will not make it level
7) Also thinking instead of plastic packers, i would use 2 nuts topped with a good washer and rest the joist on it and drill a screw/bolt through the joist into the concrete (see pic) .. does that sound something doable? .. probably glue it all together too ..
8) I dont like dynabolts, dont have an angle grinder .. so ankascrews or ramset loxin screws is what i'm thinking..  
In addition to that:
- I've been looking at getting 4.2m pre-cut lengths of hardwood (90x19mm) to just lay parallel as in pics and get done with the job .. im not good at cutting and neither do i know a lot on how to connect board after board of varying length and how to do the joists underneath
- Now obviously, except for bunnings, i can't seem to find a timber supplier who could provide me with 4.2m precut
- Bunnings, the 3 ive visited have a max of 10 lying around .. i need probably 65 lengths to do the job .. any ideas where to source these (i'm in Sydney North-west)?
- One timber supplier has got 3.9m lengths.. so not sure if i can do something with that ..
- Thinking of a 4mm gap .. is that too much?
- Thinking of getting a mdf/hardboard of 3/4mm thickness and using that as the gap .. does that sound ok? 
Sorry if i've written too much, just dont wanna write half the things and let you wonder  :Smilie:

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## Ken-67

Good information you've given us. The 70 X 35 on flat would work, with fixings at about 500mm to minimize deflection. I would fix a strip of plastic dampproof to the underside of the joists, and I would not use nuts as packers. You need packing the width of the joist, or it will rock, and you don't need that much packing. You only need about 5mm or 6mm, just enough to allow any water to run through. You can buy bags of plasic packers in different thicknesses, and plasic will not be affected by the water either. For fixing, I would use countersunk dynabolts. 
4mm to 6mm gap in the boards is fine. MDF or hardboard can get squashed between board, and then get very hard to pull out, I usually use pieces of 6mm plastic. Even if it does get a bit tight, it will slide out easier.
You would be pushing to find someone to supply that many pre-cut board, and if you did you would probably paying twice the price. If you don't have a mitre saw, it might me worth the investment for all the cutting you are going to be doing. You won't need the more expensive brands; one of the cheaper ones will do the job, unless you plan on a lot of future renovations.
 When you do buy your boards, unless they are the full length you need, don't buy all the same length. You need a variety of different lengths so you can stagger your joins.
Hope this helps. Good luck.

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## bluemetal77

Hi, thanks for you reply. 
I did go and see the 35x45mm joists .. and yeah i dont think those will work unless they are flat on ground and not hoisted up 5mm with the packers at distances. Having said that, the 35x70mm will do the job (as you suggested) however, that would mean the decking will sit 15mm above brick level .. which is still at par or below the sliding door frame .. not a biggie for me .. but when comparing solutions .. which is preferable: 
1) Use 35x70mm joists with packers of 5mm at regular intervals, OR
2) Use 35x45mm joists with a continuous packing strip all along the slab floor (the only issue i see here is if the slab is a bit uneven, i'll have to insert some packers anyways) 
Where can i get the continuous packing strip? What is it called? 
Yeah I am seriously thinking of getting a Mitre Saw, i do have a Jigsaw which i might use if the protruding boards need to be cut (or should they be grinded?) 
So turns out this Bunnings i visited has heaps of hardwood decking and definitely a lot more than 4.2m in length .. now the only thing is, if i want a border then i'll get 4m lengths and do a border .. how would i put the border board as the joists will be parallel not perpendicular? .. just put 2-3 joists together? 
I couldn't see countersunk dynabolts .. maybe they were there but i got blinded as i usually do at bunnings and the their shelves! .. but then if i'm using 70mm joists on the vertical, that wont be a preferred method of drilling through .. use angle brackets instead? 
More thoughts on this later .. preferably with some more diagrams  :Smilie:

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## Ken-67

Ideally decking should be below internal floor levels, to create a water barrier. If you can use 45mm timber and still get that step, it would be a much firmer deck. I would not put continuous packers under the joist. You need it packed clear of the concrete to allow drainage of any wate that gets there. You could put the joists standing up and using brackets, but you will still need to pack it for drainage,If you want to put a border board, yes, you will need a double joist at the end with a space between. If you just leave the cut ends, lay the boards overhanging, then cut them all with a straight-edge, using a jig saw or a circular saw.

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## shauck

I would prefer a circular saw to cut the ends as a jigsaw tends to cut on an angle.

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## bluemetal77

> If you can use 45mm timber and still get that step, it would be a much firmer deck. I would not put continuous packers under the joist. You need it packed clear of the concrete to allow drainage of any wate that gets there.

  OK, so the treated pine joists that would work are 35mm x 45mm .. how much flex do you think these have? in the sense, that if i pack a plastic 6mm packer (of 100mm length) at 100mm intervals .. would that be an overkill? (considering 4400mm lengths .. this would be 22 packers) .. or do you think the joist would still hold okay if i put a packer every 200mm ..   
Also, which side should be facing the floor, the 35mm .. or the 45mm? .. I'm thinking if its quite flat on the floor, i wouldn't need dynabolts .. a normal light-duty anchor should do, like this one, Ramset Australia or no? Or maybe use this Ramset Australia at ends and middle and the rest can be the light duty ones? .. and i'm thinking the same length to be inside the concrete as above .. meaning if above is 45, the inside should be 45-55 too.. 
I'm going to get the Mitre saw and cut the pieces to length because i will need some cutting anyways, for the main area and the steps .. now i do appreciate that even if i had the pieces cut to length .. the final installation might make some protrude a few mm out .. so i would sand them to level .. is that a preferred method? or you reckon i should let the pieces be longer to start with and then run a jigsaw to level them out? 
I can make a wooden jig to run the jigsaw against while clamped to the boards .. so that might help in the straight cut .. same with circular saw, its hand driven so it could go in any direction! (unless on a jig)

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## bluemetal77

> I would prefer a circular saw to cut the ends as a jigsaw tends to cut on an angle.

  You can adjust the angle on the jigsaw .. so if you make it -1degree .. it might cut straight! .. anyways, the edges will have a border going around it .. so hopefully the angle wont be noticeable, but a crooked cut would be amplified with the straight running border .. freaks me!

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## shauck

The border will cover that up nicely.

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## bluemetal77

Ok, good news, found a Bunnings that has taken brand new delivery of Merbau decking and is surprisingly on promotion at $4.98/lm .. I've found 4.2m and 4.5m lengths which i can get n cut myself .. so am going for that .. super excited now! .. Will be there 1st thing Saturday morning to sort out the deck spans myself! 
Now to somehow arrange delivery as i'm a family guy with a small sedan  :Smilie:

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## Ken-67

Sorry, Bluemetal. theres'sa bit of misunderstanding. When I mentioned 45mm, I was referring to 70 X 45 as against 70 X 35. 35mm would not be ideal as a joist width. Having said that either size would be fine layed on the side, depending on the available height. 
If you use 35mm you would only need packers about every 400mm; with 45mm you could spread them to about 600mm. This, of course depends on the quality of the timber; you can add more if you feel there is too much deflection between.
Using the Ramplugs would depend on the quality of your concrete, Remember, there will be a lot of movement on the finished deck, that could transfer down to your fixings. This, over time, could possible cause some of the plugs to loose their grip if the initial insertion is not sound. This, again, would be up to your own judgement about conditions.

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## bluemetal77

Hi Ken, thanks!
I'm eventually going to use these from >Ramset Australia< Dynabolt Plus Sleeve anchors with the countersunk head so that it doesn't interfere with the board above. So yeah the ramplugs did look flimsy for this job when i checked them out at bunnies. Btw, i could only see Zinc plated on stock, would they be okay or do i need to get stainless steel or galvanised? (considering they will be inground through the joist and covered. I haven't worked out the spacing of the dynabolts yet .. considering 4.4m lengths .. i'm thinking alternating between 5 and 6 bolts per joist .. since they'll be laying flat anyways .. 
I've found a treated pine joist at 42mm width so will go with that and will see how much the packers can be spaced .. not to cause the see-saw effect .. also thinking of putting the protectadek strip over it (this will also cover the dynabolts) and a dampcourse tape along the outer edges where i know sometimes a bit of water ponds up while its raining really hard and long (it goes away into the drain once the rain lightens) .. is it a good idea to paint the joists or would that be an overkill? 
Thanks for letting me bounce off ideas .. some hit back really hard n those one help the most  :Biggrin:

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## bluemetal77

Ok so attached are the 2 ways i can fix the joists to the concrete. There will be 12 of them approximating to about 450mm centers .. 
Which one do you all think, of the 2, should i be using for dynabolting to concrete? The one with 7+5 bolts per joist .. or 5+4 bolts per joist? Remember, joist 1 and 12 will hold the border board and joists 2 and 11 will be the joist for the end of the boards .. 
Thanks!

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## bluemetal77

Ignore my last post .. I'll bolt down the joists at every 500mm .. because i just realised the joist can flex and that won't be good for the deck above! 
After a 5 hour marathon at Bunnies i finally have all my hardwood in the min lengths i require ... n some more .. couldn't be happier with Merbau 90x19mm kiln dried (under side reeded) for $4.98/lm... so now that the wood is in the pocket .. i'll start gathering other stuff around decking .. still a few weeks before i start building it!

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## bluemetal77

Ok, so I've worked out the joist spacing .. its not the usual everyone recommends .. its sitting at 485mm centers .. now the reason its at that is that helps me get all the joists evenly spaced .. plus my joists are 70mm wide (not the usual 35 or 45mm wide) .. because its a low deck on concrete i'm laying the joists flat with packers .. adding another joist will get the centers to something like 370mm .. which seems an over-overkill ! 
So will a 485mm center be okay? Considering that the joists are 70mm .. meaning an extra 35mm support on each each of the joist for the decking board ..
Thanks!

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## Ken-67

485 centres should be no problem.

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## daves

Hi all just new to the site and need to get a simple deck plan drawn to submit for a permit. I'm on the Gold Coast and have no idea where to start. Any information would be appreciated
Thanks

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## bluemetal77

> Hi all just new to the site and need to get a simple deck plan drawn to submit for a permit. I'm on the Gold Coast and have no idea where to start. Any information would be appreciated
> Thanks

  I think you need to start a new thread with a whole lot more information than just the 2 lines you've written .. seriously!

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