Newly laid Indian sandstone slabs lifted & pointing crac

[pls1]

I laid a new patio using Indian Sandstone late last year. Part of the patio was laid over a compacted base of sharp sand/aggregrate using a 10-1 sharp semi-dry sand/cement mix and 4-1 moist mix for pointing. This bit is ok.
The other half of the patio was laid on existing concrete steps. The mix used here was slightly stronger (& wetter) at 8-1 and 4-1 moist mix for the pointing. I've noticed with this part however that quite a few of the slabs have come away from the bedding and the pointing has broken up. One of the pictures also shows the bedding material where it was buttered for the edge of the step flaking away.
I know its been very cold recently and a lot of frost. Is it likely this is the cause or something else?

 

[pantsmachine]

This is only a guess but could it be that there is a water layer getting in below the slabs onto the concrete area, not being able to drain away and then freezing and causing the damage?

P.S i had 6 of my indian sandstone slabs come away from the mortar bed and it was down to the freeze last month(freshly laid in January what else can i expect). It's just lucky only a few were affected. I'm sure someone will be along with more experience soon!

 

[Thermo]

what youve laid it on is the problem. you should have laid it on a wet bed of mortar in the same way that brickwork is laid. there is no suction from the dry/semi dry mix and its not strong enough. in time th erest will probably go the same way. the pointing is going as the slabs are moving

 

[pls1]

what youve laid it on is the problem. you should have laid it on a wet bed of mortar in the same way that brickwork is laid. there is no suction from the dry/semi dry mix and its not strong enough. in time th erest will probably go the same way. the pointing is going as the slabs are moving

When you say mortar, presumably it would be a sharp sand/cement mix and not building sand/cement ?

Also what kind of strength should it be for laying on concrete 4:1 ?

 

[Thermo]

it can be either sharp or building, but it looks like its been laid on a dry or semi dry mix, which is no good for slab laying. The mix needs to be roughyly the same consistency as for bricklaying. Try an experiment. knock up some semi dry mortar and lay one slab on the concrete. Make the remaining mortar wetter and lay another slab on it. Leave it 30 minutes and see which one is harder to take back up.
1 :6 mix is fine. Was the pointing just brushed into the joints?

 

[elevy]

my builder just laid indian sandstone in my patio about three weeks ago and now i can see water with some white chokey staff seeping from the pointing. is this normal or he did not preper the ground properly.
any ideas ?
thanks

edd

 

[r896neo]

The White stuff is efflorescence and should go away. It will be made worse by some laying methods, i.e. using a very wet building sand mortar and can be more problomatic over an impermeable base like concrete.

What is it layed on (i.e sub-base) and what was it bedded on? (i.e grit sand mortar?)