[trekkor]

There should be no hollow sounds...Ever!!

Hollow means no bond. It is being held together by the grout and still has the ability to move, leading to the cracks.

Flagstone is usually pretty dusty and needs to be washed before installation. Add mortar that is too dry and water mixed ( no acrylic ) and you will get a broken bond.

The grout should have no pin holes. If it is the grout below the water line tile you should request epoxy grout to avoid staining.


Go around the entire job knocking with your knuckle, looking for hollows and mark them with blue tape. Insist these pieces be reinstalled.

If you let it go, you will have to pay to have it repaired later.


KT