Patio with sandstone roof tiles!!! - What bedding mix

[shirelets]

Previous house owners 15 years ago badly laid a 7m x 7m patio (people weight only) using old surplus fairly soft Cumbrian sandstone roof tiles. These are 15 to 30mm thick - so 'Tiles' by paving expert definition - and various sizes up to 750 x 750mm. Effectively they are large crazy paving as many broken or not fully rectangular. They are bedded on 50mm to 75mm of sand on top of hardcore, so now all uneven with joints and several 'tiles' breaking up! We prefer to re-use them if possible as even 'cheap' Indian Sandstone would be getting on for £1k. Can't fathom from this superbly informative site whether to use semi dry 8:1 mix with sharp (grit) sand presumably approx 50mm deep, or mortar grade IV 7/8:1 soft sand and plasticised cement e.g. Blue Circle to same depth. Would prefer mix with at last part soft sand as there's a lot of it spare (approx 2.5 cubic metres) when we dig out 50mm to replace by a proper cemntitious bedding! Or must we bite the bullet and spend the £1k on new slabs? Any advice much appreciated thanks.

[mickavalon]

Don't replace them if they'll do what you want, but don't lay them just with Building sand, especially 50mm thick, it's not good practice.
For the cost of sand, I'd ditch the Building sand and lay them on the 8:1 Grit sand, maybe go for half Grit and half Building if you want to use some of it up. I wouldn't really bother with using any really small pieces either or any that seem to be too crumbly or weather damaged, I'd replace with some new or re-claim sandstone.

[haggistini]

id have to agree i would use some of the brush in resin compounds for jointing tho !! reclaimed is the way forward i think!

[shirelets]

Ta for replies. I'll use mixture of grit (sharp) sand and existing building sand to reduce my sand mountain! Presumably OPC (no additives) OK for this. Will mix moist 8:1 (can't thump the slabs onto dry mix or will crack) and will lay 35 to 50mm depth after compacting existing sand over existing hardcore if I can scrounge a whacker. Will cut slabs to fit much better and minimise gaps. Dreading the pointing and it all cracking up after a few years .... more reading and deciding what to use!

[mickavalon]

Try Flowpoint by Instarmac, we use it all the time, just leave a slurry trap for hosing off.