Advice on sandstone paving - Hollow sounding flags

[Peerbo]

Hi guys, Have just had a patio installed by a company at our house. Its about 25sqr mtrs of Indian Sanstone. The job itself looks good and when it was completed was advised to stay off of it for 24hrs. When i did eventually walk on it for the first time after about 4 days i noticed that a slab sounded hollow as i walked on it. After a bit of an inspection I have noticed most of the slabs sound hollow. Is this right? Pretty sure it was layed on a flat bed of morter not spotted but the night after it was done we did have an unexpected frost in the morning. And we've had a bit of rain on and off for a couple of days. Some of the dry morter at the egdes that i can see looks grey and crumbly. Has this effected it? Any help or info would be much appreicated!!

[TheVictorianCobbleCo]

Its not normal for all of the pavers to sound hollow,sometimes one or two might not "bind" with the pug. If the temp dropped to close to freezing the pavers might have delaminated from the pug (the pug not dried and then freezing). Check for movement of the pavers, if they do move, its a redo. Crumbly grouting does point to the grout not "going off", either too much water around or freezing. But LLL and others will give you more detailed advice.

[lutonlagerlout]

a photo would be a massive help peerbo
sometimes if indian stone is dry bedded it can sound hollow,
the main thing is that the slabs are not moving from downwards weight (please dont start poking and pulling at them) and that the pointing is intact
LLL