Sandstone patio laid and hollow sounds - Patio, individual bedding, hollow sound

[TazMan]

My 4m x 4m patio has been laid with indian sawn sandstone.
There is a mass concrete sub-base. The bedding layer is a sharp sand/cement mixture with individual bedding in places. Compacted by hand (no wacker plate).

I noticed there was a hollow sound walking on the flags/slabs. Some were "rocking" from my spot check. The contractor told me the rain would fix it, and the grout would too.

It's been a week and another 2 are visibly moving. This time I was told it's because sand is soft. And also that the natural stone isn't all the same thickness, differing by 5mm on some.

As the work isn't complete still, I haven't paid the remainder balance.

Q. Is the hollow sound normal? (It is not the dab/dob method)
Some are hollow, some aren't. The hollow ones feel like they have a bit of give to them. I haven't jumped on them yet!

Q. How can I assess if it is correct as I do not wish to lose a lot of money over this.

[lutonlagerlout]

he is a liar,hollow sounds indicate a void under the flags
rockers need to be removed and relaid on a full bed of new bedding
also the difference in size should be accommodated by bedding
a picture would be handy but it sounds like a fail from here
LLL

[TazMan]

Thank for the response.
What of the hollow ones that don't rock at the moment (wet weather right now in London)? Should they be re-bedded and tested for the hollow sound?

[lutonlagerlout]

normally a hollow sound when tapping either signifies a void under the flag or de lamination of the flag
neither of which are good
the slab/flag needs to be in full contact with the bedding
rockers can be sorted by careful pointing,but you shouldn't really be walking on the patio, till its pointed anyway
different people use different techniques but i always use a wet mix for sandstone,due to the uneven nature of some sandstone its harder to get full bedding with a dry mix
voice your concerns to the contractor and get any promises or guarantees in writing from him
LLL