Thickness of bed on driveway flagging

[slickboy]

Hello. I've asked quite a few questions on this site and always receive good solid advice so I'm just thanking Tony and everyone else in advance for any the replies. They are much appreciated, this is a fantastic resource.

Anyhoo.... I've been asked to lay six sides sawn flags as a driveway on an existing (and in good condition and at least 100mm thick) concrete hardstanding. The flags range from 50 mm to 75mm! I haven't seen them yet though. Given their thickness and the concrete base, how deep would the bed have to be and would it need to be concrete rather than a 4/1 gritsand/cement mix? I usually lay Indian Sandstone driveways on a full strong concrete bed at least 50mm thick and only use the thicker flags.

[Tony McC]

Use the same mortar as normal.

As this is a driveway, I'd want to be sure the mortar adheres to the concrete base, and that the flags adhere to the mortar, so I'd make sure the base was clean, and I'd probably use a slurry primer on the underside of those flagstones, given that they have a sawn rather than riven or textured finish. I'd also consider acid etching the concrete base to ensure a really good bond.

More on slurry primers here

[slickboy]

Thanks for the reply. By the same mortar as normal do you mean 50mm of gritsand/cement?

[Tony McC]

Aye!