Raised indian sand stone circle - Right way

[jack the slab]

I wont go on about how good this site is - nuff said
I intend to lay an indian stone 2.85 metre diameter circle on a 6" raised concrete slab.
I was thinking of putting a good 75mm hardcore base,wakerd down, fix pegs at regular intervals around the edge of the circle and bend strips of 6" hardboard round the pegs to form the circle. I will then fill the circle with concrete what mix is best ? I will use the top of the hardboard to screed a flat surface, could I lay the circle onto the wet concrete or wait untill dry and use a 10:1 semi dry mix as explained in numerous other links ? I would also like to lay 2 rows of granite setts around the circumference of the circle at the same level as the Indian sandstone circle and finish off with a kerb edging on end around the circumference of the setts, whats the best method to lay these ?

[Tony McC]

Why not forget about the strips of hardboard and circumference pegs and simply lay the circle directly onto 100mm depth of 1:3:6 semi-dry concrete, starting with the centre stone, and working your way out, one ring at a time, ensuring there is a touch of fall out from the centre out to the edges? Then, once you've got all of the circle laid, and you've balanced-up the joint width, lay your sett edges and kerbs on the same mix of concrete, bringing up the haunching at the outside edge.

[jack the slab]

Thanx for a speedy response.
Sounds ok, but i prefer to be able to keep nice clean sharp lines and hauncing the concrete up, I would not be able to lay the edge kerbs and then flags. Is laying on the concrete better than a semi dry mix ?

[Tony McC]

Laying the edges before the flags is completely arse-about and more or less guaranteed to cause problems. These circles are notoriously difficult to space precisely, and even if it say summat like 1760mm radius on the instruction sheet, by the time it's laid on your site, it will be 1700mm or, more likely, 1850mm.

If you've started with the edges, cast them in concrete at precisely 1760mm, you can be certain the circle will either not fit at all or will end up with a 50mm gap between edges and flags.

And what have "nice clean sharp lines" got to do with anything? This is a circle of Indian riven sandstone paving edged with granite cubes - you don't have a snowball in hell's chance of maintaining "nice clean sharp lines"!

The concrete mix IS a semi-dry mix - it's just that, at a depth of more than 50mm, a sand/cement mix isn't strong enough, so we switch from mortar (sand + cement) to concrete (sand + cement + gravel)