I have just bought some B&Q adhesive backed vinyl tiles to put on top of the existing thermoplastic ones in my kitchen. I've just noticed that on the tile box it says they are not to be put on top of asphalt tiles or thermoplastic ones. Can anyone tell me why? They don't seem to know at the branch where I bought them, and the B&Q Helpline seem very slow to respond. Thanks for any advice anyone can give.