external slab

Does anyone have advice on how to construct a concrete slab to hold a hot tub and sauna.
I'm interested in how thick to make the slab, are ground beams required, how to prepare the ground, what type of steel reinforcement to use.
I live in Melbourne, Australia, so it never freezes, but the soil is high in clay. The slab will be about 6m x 4m and I will pave it with slate or sandstone tiles and I'd lijke to do as much as possible myself.
Thanks in advance for your replies.
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here in buffalo ny usa you take 5 copies of your property survey to city hall permit office and they tell you where you can put it on your property and take some permit money. the local concrete company will refer you to their customer contractors who pay their bills and do good work. we have attempted playing with cement and with our half-experienced helpers and the wrong weather your slab will finish uneven and poor. they will determine what foundation depth and drainage is required in your yard's soil. but when you are done you will be still be wishing your heater pump wasn't so noisy. so hunt that item down first and find a satisfied customer with a quiet spa you can listen to. see also: http://www.google.com/search?num &hl=en&lr=&newwindow=1&safe=off&rls=GGLG%2CGGLG%3A2005-52%2CGGLG%3Aen&q=concrete+slab+to+hold+a+hot+tub+and+sauna.+&btnG=Search
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The details are not difficult, but too long to go into here. A good DIY book will give you more details.
In most cases, you dig the ground out allowing for a 4" slab and level it. pack down any loose dirt.
You frame the perimeter with 1 x 4's and stakes in the ground. The frame must be level as you are using it to screed the concrete when poured. With that in mind, the stakes should not be above the frame.
There are different types of reinforcement that can be used, but the home center will have a heavy wire mesh screen that works well.
TIP: Before you order the Reddi Mix truck, be sure you have all the tools in place, trowels, floats, and most important, a helper or two with strong back.
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Thanks for that.
Can anyone tell me should I put down gravel first & if so how much & does it need to be compacted? Should the slab be thicker at the edges?
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check this out, it will give a lot of info w/ little effort
once you've digested it, you'll be able to ask more questions to fill in any blanks
cheers Bob
http://www.quikrete.com/diy/searchprojects.asp
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