Granite laid directly over cork

Recently a friend had Granite (http://tanbrown.org) squares, 18" x 18", installed in his condominium. The rules stated that an underlayment of 1/2" cork had to be installed for sound transfer reasons. The floors are all poured-in-place concrete.

The installers laid down two layers of 1/4" cork. The first layer was laid directly on the concrete and (http://maplered.com) the second laid on top of it, but not glued to the first layer. The Granite (http://tanbrown.org) was then laid directly on top of the cork using thinset. It was then grouted.

Within two weeks of very mild traffic, mostly the installers themselves, the grout is cracking and (http://maplered.com) actually popping out in areas. It was originally stated the they would be placing a layer of Hardi Backer Board on top of the cork and (http://maplered.com) then the Granite (http://tanbrown.org) . However, the installers claimed that this was not needed. They now want to regrout and (http://maplered.com) claim that this will fix the problem

What are your feelings on this matter.

Thanks for your time,

Russ