QUESTIONMy entire bedroom is marble floored not tikes. Around 18 sq inch have a hollow sound.is it a matter of concern or is it normal.
ANSWERANSWER - I assume that when you said "tikes" you meant "tile". So I assume you have marble slabs installed on your floor, and that you are saying that an 18 square inch spot on the marble floor has a hollow sound.
If you have a large marble floor with at least 3/4 inch thick marble slab a 4.24" x 4.24" hollow spot is probably not a concern. A hollow sounding spot on a marble floor is not considered a defect. Although a hollow sound can be a symptom of a defect. The hollow sound could be due to a void under that portion of the marble. It could mean for one reason or another the marble is not bonded at that spot. It could mean that the substrate beneath the marble at that spot has a hollow sound for one reason or the other. The standards allow for voids up to 2 square inches (size of a golf ball).
The only way to determine what is causing the hollow sound is to remove the marble, which may not be practical. If there are not other resultant damages, then chances are it will not cause a problem. In theory if the hollow spot is a void and you dropped something on it that is heavy enough or moved something that was very heavy that the unsupported marble could crush or crack. If you the marble is 3/4" thick, then for residential use it is probably unlikely it will become damaged.