# Forum Home Renovation Concreting  Cost of suspended patio slab

## frog_hopper

Our house is built on a sloping block (double story brick house) with the second story at the back of the house being at ground level.   
We want to build a patio area and are considering a suspended concrete slab. The reason for this is that there is a void at the back of the house where the patio would start (where the ground slopes up) and then it is solid ground.  The patio area would suspend both void and solid ground area.  
Any ideas how much a suspended concrete slab of about 4m x 6m will cost? I am wondering if this is a realistic option cost-wize? 
The other option is to build a deck over the void and pave the rest.  
We cannot back fill with dirt as this there is a downstairs rumpus area that we need to keep clear of dirt.

----------


## Terrian

think of a 5 digit number, then double, add an extra 0 at the end, there is your ballpark figure  :Smilie:  
On a more serious note, you will need to get some quotes, but do be prepared for for a large number, Suspended slabs are not cheap.

----------


## Metung

I did a 7x6m approx. suspended slab on a reinforced concrete block garage using Bondek as formwork. Cost roughly  $10,000 all up for the slab, excluding support.

----------


## Terrian

> I did a 7x6m approx. suspended slab on a reinforced concrete block garage using Bondek as formwork. Cost roughly  $10,000 all up for the slab, excluding support.

  to put it in perspective, a slab that size on the ground would be somewhere around the $2,000 mark  :Smilie:

----------


## pawnhead

> to put it in perspective, a slab that size on the ground would be somewhere around the $2,000 mark

  Get real  :Rolleyes: 
With thickened edges there'd be 5m3 of concrete, so there's half your budget blown. Once you've paid for excavation, leveling sand, fortecon, reo, edgeboards, are you going to get a labourer to do the prep, a formworker to do the edgeboards, a steely to do the tie up, and a concretor and labourer to do the placement for a couple of bucks? Even if the same guy did it all, I doubt that he'd work that cheap.
If it was straightforward, then you could double that figure, and you'd still get quotes a lot higher. Of course if you don't count the labour and profit margin, then you'd be about right.

----------


## Metung

For interest's sake the rough break down was: 
$3000 for Bondek and reinforcement
$5200 for pouring of slab (6.5 cub.m. average thickness of 150mm and 40MPa concrete incl. skip/crane hire)
$1000 for prop hire, preliminary boxing and labour for Bondek and reo placement. 
I had the Bondek and reo and a local builder quoted me over $9000 to do the placement and pour which I thought was a bit excessive. It took me a while to find somebody else who would do it but ended up saving a bit which made the exercise wothwhile. I also had the "pleasure" of doing that little bit extra myself. 
Getting back to the original query, I reckon if you want something that will last and that you don't have to worry about in the forseeable future, then the suspended slab would be the way to go. Like a lot of things, if you put your money upfront then you can generally reap the benefit in the long term. At least I hope that's the go or I'm in for some strife.

----------


## frog_hopper

Sounds like it may be over kill for a patio area, although it would be good to have a uniform finish (i.e. all tiled) rather than deck and then pavers.   
Thanks for your help.

----------


## DNL

Frog - have you considered building the deck from steel - then solid floor sheeting and tiling on top of that for the consistent look? It would have to be cheaper than concrete. 
I don't know if there would be any movement - but you could always build the sub structure with narrower spans between posts and joists to provide greater stability. 
cheers
Dave

----------


## Terrian

> Get real 
> With thickened edges there'd be 5m3 of concrete, so there's half your budget blown. Once you've paid for excavation, leveling sand, fortecon, reo, edgeboards, are you going to get a labourer to do the prep, a formworker to do the edgeboards, a steely to do the tie up, and a concretor and labourer to do the placement for a couple of bucks? Even if the same guy did it all, I doubt that he'd work that cheap.
> If it was straightforward, then you could double that figure, and you'd still get quotes a lot higher. Of course if you don't count the labour and profit margin, then you'd be about right.

  7/6/.1 = 4.2m3 of concrete, say 20mpa (good enough for a garage floor) at $150 per m3 = $600, add about $350 for reo (F82), $60 per hr for a bobcat, lets be generous and say 2 hours, a m3 or so of crushed rock ($48per m3) and you are up to $1140, add $1,000 for labour and you get the "somewhere around the $2,000 mark" that I was talking about.  
I have done 6mx6m slabs for somewhat less as I know people in the game, so the above prices are what I would be paying if I just walked in off the street for the products 
So how much are you paying for your concrete ?

----------


## Planned LScape

> 7/6/.1 = 4.2m3 of concrete, say 20mpa at $140 per m3 = less than $600, add about $350 for reo, $60 per hr for a bobcat, lets be generous and say 2 hours, a m3 or so of crushed rock ($48per m3) and you are up to $1140, add $1,000 for labour and you get the "somewhere around the $2,000 mark" that I was talking about.  
> So how much are you paying for your concrete ?

  I would agree with too Terrian, you wouldnt have to pay formworkers, steel fixers etc as the concretors do it all themselves for a simple ground slab. Roughly $50/m² for a concretor to do an ordinary conc slab, which includes formwork, base and laying, add minimum fee for machine excavation if needed and it's between $2000-$2500

----------


## Terrian

> I would agree with too Terrian, you wouldnt have to pay formworkers, steel fixers etc as the concretors do it all themselves for a simple ground slab. Roughly $50/m² for a concretor to do an ordinary conc slab, which includes formwork, base and laying, add minimum fee for machine excavation if needed and it's between $2000-$2500

  those interstaters much be getting ripped off something shocking if they are paying much more than my rough figures  :Redface: ) 
min machine hire is for people who don't have mates that work for a slab of Jim Bean & coke  :Smilie:

----------


## pawnhead

> I have done 6mx6m slabs for somewhat less as I know people in the game, so the above prices are what I would be paying if I just walked in off the street for the products 
> So how much are you paying for your concrete ?

  Fair enough. I was just guessing somewhere between $180>$200. Although I haven't seen an engineer specifying anything less than 25mpa if you're going to drive a car on it. I suppose it wouldn't be that much dearer than 20mpa though.  I think they'd design thickened edges as well, with stirrups and trench mesh, so that would bump up the reo a bit. And I'd want some quality fortecon under it if it was my garage, so that's another $150. And edge boards must cost something. They don't last forever.
I didn't realize that a bobcat driver would throw in his float for a slab of Beam either, so I thought it would be a bit more than $120 to get him out of bed. You'd better at least add the cost of the slab  to your estimate though (unless it fell off the back of a truck :Wink: ). 
I reckon you'd be hard pressed to get a _decent_ slab of that size poured for under $3,000, and you'd  almost certainly get quotes a lot higher. But admittedly, you seem to know your numbers  on a budget slab.  :2thumbsup: 
I'm sure that you'd be absolutely flat out like a lizard drinking, quoting $50/m2.

----------


## Planned LScape

I think it is only  a patio though, not a garage/shed floor for vehicular traffic, which would obviously have thicker concrete, reo, thickened edges etc which would considerable increase costs. Shed slabs mostly need council approve also and engineer drawings

----------


## pawnhead

> I think it is only  a patio though,

   :Doh: 
Well there goes all my arguments.
There's no 'out' for me now.  :Crutch:

----------


## Terrian

> Well there goes all my arguments.
> There's no 'out' for me now.

  hell no, you are totally up the creek now  :Smilie:   
p.s 1) 25 mpa is only about $10 - $15m3 more than 20 mpa,  thats just 40kg of cement difference. 
p.s 2) 20 mpa with f72 is enough to handle 22tonne tandem trucks parking/driving over it
p.s 3) slab of JB & cola was payment for 8hrs+ of 4 tonne excavator used in my back yard, thats real mates rates  :Smilie: 
p.s 4) on further thought, $200 would be min hire for a bobcat, 4 - 5 hrs, even if the job took 10 minutes to do (working on $50ph cash job!), anyone charging 'float' fee is to be avoided IMO.

----------


## Terrian

> I reckon you'd be hard pressed to get a _decent_ slab of that size poured for under $3,000, and you'd  almost certainly get quotes a lot higher. But admittedly, you seem to know your numbers  on a budget slab.

  That would have to depend on your version of 'decent', I would consider a nice finish, little to no visible surface cracks, able to park a 22t truck safely as being decent, your version may differ  :Smilie:  
A little background, for about 13 years I worked in garden supplies, 4 of those years running a yard that also had mini mix concrete.  
Not all that long ago I poured 6m x 4.8m slab, * 20mpa, 150mm thick, f72 reo, 12mm reo bars, I had change left over from $600 (somewhere to park the caravan, will later widen it from 4.8m to 6m and put my workshop on it).   

> I'm sure that you'd be absolutely flat out like a lizard drinking, quoting $50/m2.

  probably closer to $55 m2, that works out close enough to $2k for a 6x6 slab  :Redface: )  
* knowing my mate, it would not surprise me if it was 25mps, heck, it could have been 32mpa

----------


## pawnhead

Yeh you guys obviously know your concrete a lot better than I do.
Some interesting info there.  :2thumbsup:  
I'd better shut up now, and let this thread become buried somewhere in the bowels of WWF.  :Tongue:

----------

