We've just had a new heating system put in which has left some spaces in our porch floor tiles where the old boiler came out, plus the tiles are looking a bit tired now, so I want to lay some more down. The original tiles were laid over a solid concrete floor & there's enough height to lay new tiles over the old ones, so I'm wanting to find out if this is wise / normal practice for my situation. I've read about floor membranes etc, but I guess these only apply to damp areas like bathrooms.