The wood tiles can "bridge" about 3/8 in. of vertical mismatch in a concrete sub-surface as long as any such cracking does not lie directly below the join between adjacent tiles. Excessive unevenness in a concrete surface will need to be repaired with a patching compound or resurfaced prior to installation.

The SwiftTile porcelain tiles however need to be laid on smooth surface which will not allow them to "rock".