Flag on edge retaining wall

[dpatel]

Hi, I'm looking to create a retaining wall (approx 450mm high) using some old flags. I've been reading this page: http://www.pavingexpert.com/featur06.htm

I'm a bit confused by this image: http://www.pavingexpert.com/images/features/flagedg1.gif

How do you get the concrete in the cavity behind the flag? If I dig out a cavity then what keeps the flag in place while the concrete sets? I assume the earth shown above the concrete haunch (where it shows the 100mm vertical dimension) is laid on after the concrete is dry?

I suspect it's something that is obvious to those who've done this before but I'm a bit confused!!

[dig dug dan]

You simply dig out enough behind the slab to accomodate the concrete haunch, and then backfill with soil when its set.

[Tony McC]

The 'batter' (that is, the leaning back) on the flag holds everything in place while the concrete hardens. The concrete needs to be reasonably stiff - a high slump would put too much load on the flag and push it over, so a 25-30mm slump, which is stiff enough for the concrete to more-or-less support itself for those first few hours.