After six years, my kitchen’s original floor tiles had started to shift and pop up. Two years ago my contractor had pulled up many of the tiles and new adhesive was applied, but this fix did not work. Before long the tiles began to shift again, and the gaps between tiles started to widen. The main problem is the wooden sub-floor with occasional dampness under the house (pier beam) causing the wood to expand. If the tiles had been laid on smooth level concrete, I wouldn’t have this problem. And if a super thick wax sealer had been applied after the first installation, the tiles would have had a much better chance on staying put longer.