Don't do it. I did it a while back and there are many unseen cracks that can happen. When two sufaces of the tile meet each other, the friction creates gaps, which leads to cracks. You will be forever repairing.
Clean the old tiles thoroghly then stick the new tiles on using silicone applied with a gun. just make sure youre not the poor bugger who has to get them off.
You could also use a chemical adhesive paste, it sets like stone but stinks the house out, smells like nail polish remover.
Do not grout for a few days if using the second method.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local