Marble flooring at my house oscillates when we walk over it.How to rectify or resolve this issue?
There may be several causes for tiles becoming loose. The most popular are:  1). sub-floor not level. An un-even floor won't fully support the tiles. The unsupported area of the tile will slightly flex and overtime will magnify its' motion until it loosens completely.  2). Thin-set not mixed or not properly applied. The cement adhesive needs to be mixed according to the instructions. If there is too much or not enough water the tile will not bond properly. If the thin-set is troweled onto the floor with the wrong sized notched trowel or too thin a layer the tile may not adhere fully.  And 3). the sub-floor must be rigid and secure with no bounce or movement. If it is not prepared correctly by nailing or screwing loose boards down it will flex and transfer that movement through the tile resulting in a failed or loose tile.