Sawn sandstone - very hollow! - Bedding later for sawn & honed sandstone

[nigelthepelican]

I have just laid some sawn and honed sandstone onto a 40mm bed of sharp sand and cement (which had a concrete sub base). The mix was not too wet and quite a few of the slabs have not adhered to the sharpsand mix. Its all been pointed and looks great but there are a large number of hollow sounding tiles ...... do they have to come up ?

[dig dug dan]

did you add some sbr to the mix?

[lutonlagerlout]

are they moving when you walk on them?
if so they must come up
the hollow sound can be a bedding failure,i.e. not a full bed
LLL

[nigelthepelican]

thanks for the replies - no SBS wasnt used unfortunately. the flags are not visibly moving but some of them do sound like they are not bedded to anything as the base layer of sharp send and cement was quite a dry mix and the flags were tamped down on to the top of the mix

[Pablo]

Sometimes for no reason flags sound hollow even when fully supported if they're not moving and it all looks good I'd leave it be you'll not worry about it soon enough.