I recently bought a house with beautiful tiles on the inside stair case. The tiles were put directly onto wood and some are cracking. The tiles are discontinued and I have to buy them from Spain so I will only get one chance at getting this right. I've had several people come to give estimates and each has given a different opinion. One said, it needs backerboard between the wood and tiles, one said it just needs a stronger/waterproof adhesive, one said the wooden staircase is not a solid/stable piece and needs to be replaced or the tiles will always continue to crack (in other words, tear down the entire staircase and start from scratch). I'm totally confused. What is the correct way to put tiles on wooden stairs so they don't continue to crack?